Indian Tick Typhus

Infectious Disease MONDO:0000229 Pathograph 21 Show in embeddings browser Spotted fever rickettsiosis

Indian tick typhus is an acute tick-borne spotted-fever-group rickettsiosis caused by the obligately intracellular bacterium Rickettsia conorii subsp. indica. Rhipicephalus ticks inoculate the bacterium into skin; local and systemic endothelial infection produces the spotted-fever pattern of fever, eschar, maculopapular rash, headache, thrombocytopenia, and hepatic or renal laboratory abnormalities.

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8
Pathophys.
10
Phenotypes
21
Pathograph
2
Medical Actions
1
Models
8
References
1
Deep Research
🏷

Classifications

Harrison's Part
INFECTIOUS DISEASES
⚙

Pathophysiology

8
Rhipicephalus-Borne ITTR Inoculation
An infected Rhipicephalus tick bite introduces R. conorii subsp. indica into the dermis, seeding local rickettsial infection that can produce an inoculation eschar and then disseminate systemically.
inflammatory response GO:0006954 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased inflammatory response (GO:0006954). GO:0006954 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Inoculation Eschar Local dermal rickettsial infection produces the necrotic eschar.
Sca2-Dependent Host-Cell Invasion Disseminating R. conorii cells engage endothelial invasion machinery.
Rickettsial Endothelial Infection Locally inoculated rickettsiae disseminate to vascular endothelium.
Show evidence (1 reference)
PMID:41650674 SUPPORT Human Clinical
"A 55-year-old female farmer presented with fever, headache, eschar, and a maculopapular rash following a tick bite."
The patient presentation directly connects tick exposure with the local eschar and systemic spotted-fever manifestations of ITTR infection.
Sca2-Dependent Host-Cell Invasion
R. conorii uses the multifunctional Sca2 autotransporter during mammalian cell association and endothelial invasion, putting bacterial surface adhesins upstream of the intracellular endothelial infection that drives Indian tick typhus.
endothelial cell of vascular tree CL:0002139 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves endothelial cell of vascular tree (CL:0002139). CL:0002139 is a cell type from the Cell Ontology.
symbiont entry into host GO:0044409 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased symbiont entry into host (GO:0044409). GO:0044409 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Arp2/3-Dependent Actin Remodeling Initial rickettsial contact triggers host actin assembly pathways needed for rickettsial uptake.
Show evidence (1 reference)
PMID:22612237 SUPPORT In Vitro
"A rickettsial autotransporter from Rickettsia conorii, Sca2, has been shown to be sufficient to mediate both adherence and invasion of human endothelial cells and to participate in intracellular actin-based motility."
R. conorii Sca2 provides an experimentally characterized bacterial autotransporter that can mediate endothelial adhesion and invasion.
Arp2/3-Dependent Actin Remodeling
Spotted-fever-group rickettsiae engage host Rho-family GTPase and WAVE signaling that converges on Arp2/3-mediated actin filament polymerization, remodeling the endothelial actin cortex during entry.
endothelial cell of vascular tree CL:0002139 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves endothelial cell of vascular tree (CL:0002139). CL:0002139 is a cell type from the Cell Ontology.
actin filament polymerization GO:0030041 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased actin filament polymerization (GO:0030041). GO:0030041 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Rickettsial Endothelial Infection Actin remodeling enables efficient endothelial uptake and cytosolic infection.
Show evidence (1 reference)
PMID:22188208 SUPPORT In Vitro
"Receptor binding by Rickettsia proteins initiates activation of host protein tyrosine kinases, leading to Cdc42 activation and Rac-dependent activation of WAVE, which may act in parallel with other NPFs to activate Arp2/3. Finally, the Arp2/3 complex acts as the major nucleator of actin..."
R. parkeri experiments define a conserved spotted-fever-group host actin program in which Rho-family GTPases and WAVE converge on Arp2/3 during mammalian-cell invasion.
Rickettsial Endothelial Infection
R. conorii subsp. indica belongs to the spotted-fever rickettsiae whose pathogenic members invade and replicate in vascular endothelial cells, making microvascular endothelium the host-cell compartment that transduces infection into vasculitis.
endothelial cell of vascular tree CL:0002139 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves endothelial cell of vascular tree (CL:0002139). CL:0002139 is a cell type from the Cell Ontology.
biological process involved in interaction with host GO:0051701 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves biological process involved in interaction with host (GO:0051701). GO:0051701 is a biological process from the Gene Ontology.
Animal models
C3H/HeN Rickettsia conorii Malish infection mouse Mouse partially recapitulates High-dose infection establishes disseminated endothelial infection and vascular-injury-based meningoencephalitis and interstitial pneumonia; the low-dose infection produces reversible illness with rickettsial clearance and lymphohistiocytic perivasculitis.
Downstream
Rickettsial Vasculitis Endothelial rickettsial infection drives vascular inflammation.
Show evidence (1 reference)
PMID:19327117 SUPPORT REVIEW SYNTHESIS Other
"Although pathogenic Rickettsiae are able to infect and replicate in a number of different cell types in vitro, a unique property during in vivo infection is their affinity for vascular endothelial cells (ECs) lining small and medium-sized blood vessels in humans and in established animal models..."
The review identifies vascular endothelial cells as the in-vivo target that is shared by pathogenic spotted-fever rickettsiae.
Rickettsial Vasculitis
Endothelial rickettsial infection and inflammation produce small-vessel vasculitis, increased vascular permeability, and the fever, rash, and multisystem laboratory abnormalities of Indian tick typhus.
endothelial cell of vascular tree CL:0002139 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves endothelial cell of vascular tree (CL:0002139). CL:0002139 is a cell type from the Cell Ontology.
inflammatory response GO:0006954 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased inflammatory response (GO:0006954). GO:0006954 is a biological process from the Gene Ontology. ↑ INCREASED positive regulation of vascular permeability GO:0043117 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased positive regulation of vascular permeability (GO:0043117). GO:0043117 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Fever Systemic rickettsial inflammation produces fever.
Maculopapular Rash Cutaneous rickettsial vasculitis produces the exanthem.
Headache The acute inflammatory syndrome can include headache.
Platelet Activation and Microthrombus Formation R. conorii endothelial injury can activate platelets and coagulation in the injured microvasculature.
Elevated Hepatic Transaminases Systemic rickettsial disease can injure the liver.
Hyponatremia Systemic rickettsial disease can include hyponatremia.
Neurologic Involvement CNS vasculitis can produce neurological involvement.
Proteinuria Systemic rickettsial disease can involve the kidney.
Multifocal Retinitis Rickettsial vascular inflammation can involve the retina.
Show evidence (1 reference)
PMID:34345128 SUPPORT REVIEW SYNTHESIS Other
"The pathological hallmark of rickettsial infections is endothelial infection and inflammation causing vasculitis. Endothelial inflammation results in microvascular dysfunction and increased vascular permeability."
The rickettsial critical-care review connects endothelial infection to vasculitis, microvascular dysfunction, and increased permeability.
Platelet Activation and Microthrombus Formation
R. conorii endothelial injury is accompanied by TXA2-dependent platelet activation and thrombin generation in vivo, providing a consumptive route to thrombocytopenia and focal rickettsial microthrombi.
platelet CL:0000233 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves platelet (CL:0000233). CL:0000233 is a cell type from the Cell Ontology.
platelet activation GO:0030168 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased platelet activation (GO:0030168). GO:0030168 is a biological process from the Gene Ontology. ↑ INCREASED blood coagulation GO:0007596 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased blood coagulation (GO:0007596). GO:0007596 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Thrombocytopenia Platelet activation and microthrombus formation consume platelets.
Show evidence (1 reference)
PMID:8584998 SUPPORT Human Clinical
"Our results provide biochemical evidence for the occurrence of TXA2-dependent platelet activation and thrombin generation in vivo, together with endothelial dysfunction. These phenomena could account for clinical manifestations of MSF, such as vasculitis and focal microthrombus formation."
R. conorii Mediterranean spotted fever shares endothelial injury with Indian tick typhus and demonstrates the platelet/coagulation arm that can lower platelet counts during spotted-fever disease.
Rickettsial Ribosomal Translation
R. conorii subsp. indica, like other bacteria, depends on ribosomal translation of its mRNA, making the bacterial ribosome the conserved antibiotic target for doxycycline therapy.
Translation GO:0006412 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves Translation (GO:0006412). GO:0006412 is a biological process from the Gene Ontology.
Show evidence (1 reference)
PMID:24336183 SUPPORT REVIEW SYNTHESIS Other
"The ribosome is one of the main antibiotic targets in the bacterial cell."
Review evidence establishes the bacterial ribosome as the conserved target class for tetracyclines such as doxycycline.
Intracytosolic Rickettsia conorii Niche
Rickettsia species reside free in the host-cell cytosol and exploit host metabolites, so effective Indian tick typhus therapy must reach the intracellular bacterial compartment.
biological process involved in interaction with host GO:0051701 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves biological process involved in interaction with host (GO:0051701). GO:0051701 is a biological process from the Gene Ontology.
Downstream
Rickettsial Ribosomal Translation Intracytosolic R. conorii remains dependent on bacterial protein synthesis.
Show evidence (1 reference)
PMID:30148688 SUPPORT REVIEW SYNTHESIS Other
"Residing free in the cytosol of the host cell, they acquire many necessary components via transport mechanisms instead of maintaining genes for synthesizing sugars, lipids, nucleotides, and amino acids."
The review supports the free cytosolic niche for pathogenic Rickettsia species, including the R. conorii complex.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Indian Tick Typhus Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

10
Blood 1
Thrombocytopenia FREQUENT HP:0001873 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thrombocytopenia (HP:0001873). HP:0001873 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:41795239 SUPPORT Human Clinical
"Laboratory abnormalities included thrombocytopenia (56%), hyponatremia (78%), elevated transaminases (83%), and markedly raised C-reactive protein."
The pediatric R. conorii cohort places thrombocytopenia in the frequent range.
PMID:41650674 SUPPORT Human Clinical
"Laboratory findings indicated thrombocytopenia, liver enzyme elevation, and proteinuria, which, combined with clinical symptoms, strongly suggested a rickettsial infection."
Thrombocytopenia was documented as a laboratory abnormality in a PCR-confirmed ITTR infection.
Eye 1
Multifocal Retinitis HP:0032118 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinitis (HP:0032118). HP:0032118 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30451192 SUPPORT Human Clinical
"Examination showed multifocal retinitis; mostly bilateral; patients had a history of fever approximately 4 weeks prior to onset of symptoms."
A South Indian cluster of serologically proven Indian tick typhus cases established multifocal retinitis as an ocular manifestation.
Genitourinary 1
Proteinuria HP:0000093 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Proteinuria (HP:0000093). HP:0000093 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41650674 SUPPORT Human Clinical
"Laboratory findings indicated thrombocytopenia, liver enzyme elevation, and proteinuria, which, combined with clinical symptoms, strongly suggested a rickettsial infection."
Proteinuria was documented as a renal laboratory abnormality in the PCR-confirmed ITTR infection.
Immune 1
Maculopapular Rash Maculopapular exanthema HP:0040186 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Maculopapular exanthema (HP:0040186). HP:0040186 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41650674 SUPPORT Human Clinical
"A 55-year-old female farmer presented with fever, headache, eschar, and a maculopapular rash following a tick bite."
Maculopapular rash was present in the PCR-confirmed ITTR case.
Integument 1
Inoculation Eschar HP:6000793 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Eschar (HP:6000793). HP:6000793 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41650674 SUPPORT Human Clinical
"A 55-year-old female farmer presented with fever, headache, eschar, and a maculopapular rash following a tick bite."
Eschar was present after a tick bite in the PCR-confirmed ITTR case.
Metabolism 3
Fever VERY_FREQUENT HP:0001945 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fever (HP:0001945). HP:0001945 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:41795239 SUPPORT Human Clinical
"Fever and rash were universal (100%);"
A PCR-confirmed pediatric R. conorii cohort reported fever in all cases, supporting the very-frequent fever band for the R. conorii complex.
PMID:41650674 SUPPORT Human Clinical
"A 55-year-old female farmer presented with fever, headache, eschar, and a maculopapular rash following a tick bite."
Fever was part of the acute presentation in a PCR-confirmed ITTR infection.
Elevated Hepatic Transaminases VERY_FREQUENT Elevated circulating hepatic transaminase concentration HP:0002910 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated hepatic transaminase, annotated with Elevated circulating hepatic transaminase concentration (HP:0002910). HP:0002910 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:41795239 SUPPORT Human Clinical
"Laboratory abnormalities included thrombocytopenia (56%), hyponatremia (78%), elevated transaminases (83%), and markedly raised C-reactive protein."
The pediatric R. conorii cohort places elevated transaminases in the very-frequent range.
PMID:41650674 SUPPORT Human Clinical
"Laboratory findings indicated thrombocytopenia, liver enzyme elevation, and proteinuria, which, combined with clinical symptoms, strongly suggested a rickettsial infection."
Liver enzyme elevation in the ITTR case supports a transaminase phenotype.
Hyponatremia FREQUENT HP:0002902 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyponatremia (HP:0002902). HP:0002902 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41795239 SUPPORT Human Clinical
"Laboratory abnormalities included thrombocytopenia (56%), hyponatremia (78%), elevated transaminases (83%), and markedly raised C-reactive protein."
The pediatric R. conorii cohort reported hyponatremia in the frequent range.
Nervous System 2
Headache HP:0002315 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Headache (HP:0002315). HP:0002315 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41650674 SUPPORT Human Clinical
"A 55-year-old female farmer presented with fever, headache, eschar, and a maculopapular rash following a tick bite."
Headache was part of the acute PCR-confirmed ITTR presentation.
Neurologic Involvement OCCASIONAL Abnormality of the nervous system HP:0000707 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neurological involvement, annotated with Abnormality of the nervous system (HP:0000707). HP:0000707 is a phenotype from the Human Phenotype Ontology.
Coarse binding: source unspecified
Show evidence (1 reference)
PMID:41795239 SUPPORT Human Clinical
"Gastrointestinal symptoms occurred in 44%, neurological involvement in 28%, and arthralgia/myalgia in 33%."
The pediatric R. conorii cohort reported neurologic involvement in the occasional range.
💊

Medical Actions

2
Empiric doxycycline
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: doxycycline CHEBI:50845 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses doxycycline (CHEBI:50845). CHEBI:50845 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Doxycycline is first-line empiric therapy for suspected Indian tick typhus and related rickettsial diseases because it blocks rickettsial ribosomal translation in the intracellular bacterial compartment.
Mechanism Target:
INHIBITS Rickettsial Ribosomal Translation — Doxycycline inhibits bacterial protein synthesis through the conserved tetracycline-class ribosomal target.
BYPASSES Intracytosolic Rickettsia conorii Niche — Doxycycline can reach the R. conorii cytosolic compartment inside host cells.
Show evidence (1 reference)
PMID:28361787 SUPPORT Other
"Indian tick typhus and scrub typhus are commonly seen rickettsial diseases in India. It is recommended that practicing pediatricians should be well conversant with compatible clinical scenario, suggestive epidemiological features, differential diagnoses and suggestive laboratory features to make..."
Indian pediatric rickettsial guidelines identify doxycycline as the drug of choice and recommend prompt empiric therapy for diseases that include Indian tick typhus.
Azithromycin
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: azithromycin CHEBI:2955 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses azithromycin (CHEBI:2955). CHEBI:2955 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Azithromycin is a macrolide alternative for spotted-fever-group rickettsioses when doxycycline cannot be used or is unavailable.
Mechanism Target:
INHIBITS Rickettsial Ribosomal Translation — Azithromycin targets bacterial ribosomal translation through a macrolide mechanism.
Show evidence (1 reference)
PMID:34345128 SUPPORT REVIEW SYNTHESIS Other
"Intravenous doxycycline with a loading dose is the most widely used antibiotic in critically ill patients, with azithromycin as a suitable alternative."
The rickettsial critical-care review identifies azithromycin as a suitable alternative to doxycycline for serious rickettsial infection.
🔬

Diagnosis

2
Rickettsial PCR and gene sequencing
PCR amplification and sequencing of rickettsial genes can confirm acute ITTR infection and match the pathogen sequence between patient material and the attached tick.
polymerase chain reaction NCIT:C17003 NCI Thesaurus (NCIT)
Results: Positive rickettsial PCR with sequence identity to ITTR confirms infection.
Show evidence (1 reference)
PMID:41650674 SUPPORT Human Clinical
"PCR and sequencing of multiple rickettsial genes confirmed the presence of ITTR in both the patient and the tick."
PCR followed by sequencing confirmed ITTR in an acutely infected patient.
Indirect immunofluorescence assay serology
Indirect immunofluorescence can support spotted-fever-group rickettsiosis serodiagnosis, but serology may be retrospective because early false negatives occur before delayed seroconversion.
Results: IgG or IgM seroreactivity, especially seroconversion or a rising titer, supports recent spotted-fever-group rickettsial infection.
Show evidence (1 reference)
PMID:42390463 SUPPORT REVIEW SYNTHESIS Other
"the Weil-Felix test lacks necessary specificity, while the gold standard indirect immunofluorescence assay (IFA) is primarily retrospective due to delayed seroconversion."
The rickettsial diagnostics review identifies IFA as the serologic gold standard and explains why acute-phase serology can lag behind illness.
🌍

Epidemiology

1
Indian-subcontinent Rhipicephalus tick exposure
Indian tick typhus is tied to Rhipicephalus tick exposure in India and Pakistan, and ITTR has been molecularly detected farther east in Xinjiang.
Indian subcontinent tick exposure Rhipicephalus tick exposure
Show evidence (2 references)
PMID:15766388 SUPPORT Other
"The type strain is Indian tick typhus, ATCC VR-597, which was isolated from a Rhipicephalus sanguineus tick collected in India by C.B. Philip in 1950."
The subspecies description ties the type Indian tick typhus isolate to an R. sanguineus tick from India.
PMID:41650674 SUPPORT Human Clinical
"Rickettsia conorii Indian tick typhus strain (R. conorii subsp. indica, ITTR) was detected in both a human patient and an attached Rhipicephalus turanicus tick that was removed from the patient in Yanqi County, Xinjiang Uygur Autonomous Region (XUAR), China."
The molecular case report extends documented ITTR infection and vector carriage to a patient and attached tick in Xinjiang.
🦠

Infectious Agent

1
Rickettsia conorii subsp. indica
Obligate intracellular spotted-fever-group rickettsial subspecies that causes Indian tick typhus.
Rickettsia conorii subsp. indica NCBITaxon:317865 NCBI Taxonomy (NCBITaxon)
Show evidence (2 references)
PMID:22628514 SUPPORT Other
"Rickettsia conorii subsp. indica is the agent of Indian tick typhus. The present study reports the draft genome of Rickettsia conorii subsp. indica strain ITTR (ATCC VR-597)."
The genome report names R. conorii subsp. indica strain ITTR as the etiologic agent of Indian tick typhus.
PMID:15766388 SUPPORT Other
"We propose the names R. conorii subsp. conorii subsp. nov. (type strain = Malish, ATCC VR-613), R. conorii subspecies indica subsp. nov. (type strain = ATCC VR-597), R. conorii subspecies caspia subsp. nov. (type strain = A-167), and R. conorii subspecies israelensis subsp. nov. (type strain =..."
Multilocus taxonomic analysis formally places Indian tick typhus rickettsia inside R. conorii as subsp. indica.
↔️

Transmission

1
Rhipicephalus tick bite inoculation
Humans acquire Indian tick typhus when infected Rhipicephalus ticks bite and inoculate R. conorii subsp. indica into skin.
Show evidence (2 references)
PMID:15766388 SUPPORT Other
"The characteristics are the same as those of the species. Transmitted to humans through the bite of Rhipicephalus sanguineus ticks."
The taxonomic description of R. conorii subsp. indica records human transmission through bites of R. sanguineus ticks.
PMID:41650674 SUPPORT Human Clinical
"PCR and sequencing of multiple rickettsial genes confirmed the presence of ITTR in both the patient and the tick. Furthermore, the genetic identity between these sequences provided evidence that R. turanicus can act as a vector of ITTR."
Matching PCR sequences from a patient and an attached R. turanicus tick support a second Rhipicephalus vector for ITTR.
🐁

Animal Models

1
C3H/HeN Rickettsia conorii Malish infection mouse
Intravenous R. conorii Malish 7 infection in C3H/HeN mice produces disseminated endothelial infection, illness, and dose-dependent vascular-injury outcomes, modeling the endotheliotropic vasculitis shared across R. conorii spotted-fever infections.
Species
Mouse
Genotype
Wild-type C3H/HeN
Publication
PMID:7511715
Pathograph links
Rickettsial Endothelial Infection partially recapitulates fidelity: moderate High-dose infection establishes disseminated endothelial infection and vascular-injury-based meningoencephalitis and interstitial pneumonia; the low-dose infection produces reversible illness with rickettsial clearance and lymphohistiocytic perivasculitis.
Limitations: The model uses the R. conorii Malish 7 strain associated with Mediterranean spotted fever, not R. conorii subsp. indica, so it supports the shared endotheliotropic rickettsial mechanism rather than an indica-specific virulence program.
Show evidence (1 reference)
PMID:7511715 SUPPORT Model Organism
"Mice inoculated with a high dose of rickettsiae established disseminated endothelial infection on day 1, became ill with progressive increase in rickettsiae on day 4, and died with vascular injury-based meningoencephalitis and interstitial pneumonia on day 5 or 6. Mice inoculated with the low..."
The dose-stratified C3H/HeN model directly measures the endothelial infection and vascular-injury phenotypes central to spotted-fever pathogenesis.
Show evidence (1 reference)
PMID:7511715 SUPPORT Model Organism
"This experimental infection provides the best available model for rickettsial disease with endothelial infection and injury, immune rickettsial clearance, regeneration of endothelium, and repair of the vascular lesions."
The authors frame C3H/HeN R. conorii infection as an endothelial-target rickettsiosis model.
{ }

Source YAML

click to show 
name: Indian Tick Typhus
creation_date: "2026-09-28T05:48:49Z"
category: Infectious Disease
description: >-
  Indian tick typhus is an acute tick-borne spotted-fever-group rickettsiosis
  caused by the obligately intracellular bacterium Rickettsia conorii subsp.
  indica. Rhipicephalus ticks inoculate the bacterium into skin; local and
  systemic endothelial infection produces the spotted-fever pattern of fever,
  eschar, maculopapular rash, headache, thrombocytopenia, and hepatic or renal
  laboratory abnormalities.
disease_term:
  preferred_term: Indian tick typhus
  term:
    id: MONDO:0000229
    label: Indian tick typhus
parents:
- Spotted fever rickettsiosis
synonyms:
- Rickettsia conorii subsp. indica infection
- Indian tick typhus rickettsiosis
- Indian tick typhus rickettsia infection

references:
- reference: PMID:22628514
  title: Genome sequence of Rickettsia conorii subsp. indica, the agent of Indian tick typhus.
  found_in:
  - Indian_Tick_Typhus-deep-research-openscientist.md
  findings:
  - statement: >-
      Rickettsia conorii subsp. indica strain ITTR is the agent of Indian tick
      typhus.
    supporting_text: >-
      Rickettsia conorii subsp. indica is the agent of Indian tick typhus. The
      present study reports the draft genome of Rickettsia conorii subsp.
      indica strain ITTR (ATCC VR-597).
- reference: PMID:15766388
  title: >-
    Proposal to create subspecies of Rickettsia conorii based on multi-locus
    sequence typing and an emended description of Rickettsia conorii.
  found_in:
  - Indian_Tick_Typhus-deep-research-openscientist.md
  findings:
  - statement: >-
      The ITTR strain is taxonomically R. conorii subsp. indica, a genotypic
      and serotypically distinct R. conorii subspecies transmitted through
      Rhipicephalus sanguineus tick bite.
    supporting_text: >-
      The characteristics are the same as those of the species. Transmitted to
      humans through the bite of Rhipicephalus sanguineus ticks.
- reference: PMID:41650674
  title: >-
    Identification of Rickettsia conorii Indian tick typhus strain in a Patient
    and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
  found_in:
  - Indian_Tick_Typhus-deep-research-openscientist.md
  findings:
  - statement: >-
      PCR and sequencing confirmed R. conorii Indian tick typhus strain in both
      an acutely ill patient and an attached Rhipicephalus turanicus tick.
    supporting_text: >-
      PCR and sequencing of multiple rickettsial genes confirmed the presence
      of ITTR in both the patient and the tick.
- reference: PMID:22612237
  title: >-
    Identification and characterization of the mammalian association and
    actin-nucleating domains in the Rickettsia conorii autotransporter protein,
    Sca2.
  findings:
  - statement: >-
      R. conorii Sca2 is sufficient to mediate adherence and invasion of human
      endothelial cells and participates in intracellular actin-based motility.
    supporting_text: >-
      A rickettsial autotransporter from Rickettsia conorii, Sca2, has been
      shown to be sufficient to mediate both adherence and invasion of human
      endothelial cells and to participate in intracellular actin-based motility.
- reference: PMID:22188208
  title: >-
    Rickettsia parkeri invasion of diverse host cells involves an Arp2/3
    complex, WAVE complex and Rho-family GTPase-dependent pathway.
  findings:
  - statement: >-
      Host Rho-family GTPase and WAVE signaling converge on the Arp2/3 complex
      as the major actin nucleator during Rickettsia invasion of host cells.
    supporting_text: >-
      Receptor binding by Rickettsia proteins initiates activation of host
      protein tyrosine kinases, leading to Cdc42 activation and Rac-dependent
      activation of WAVE, which may act in parallel with other NPFs to activate
      Arp2/3. Finally, the Arp2/3 complex acts as the major nucleator of actin
      filaments during Rickettsia invasion of host cells.
- reference: PMID:8584998
  title: >-
    Demonstration of Rickettsia Conorii-induced coagulative and platelet
    activation in vivo in patients with Mediterranean spotted fever.
  findings:
  - statement: >-
      Acute R. conorii infection is associated with TXA2-dependent platelet
      activation, thrombin generation, endothelial dysfunction, vasculitis, and
      focal microthrombus formation.
    supporting_text: >-
      Our results provide biochemical evidence for the occurrence of
      TXA2-dependent platelet activation and thrombin generation in vivo,
      together with endothelial dysfunction. These phenomena could account for
      clinical manifestations of MSF, such as vasculitis and focal microthrombus
      formation.
- reference: PMID:41795239
  title: >-
    The first pediatric cohort of Rickettsia conorii infection in Palestine: A
    five-year multicenter epidemiological and clinical analysis.
  findings:
  - statement: >-
      A PCR-confirmed pediatric R. conorii cohort documented universal fever and
      rash, hyponatremia in 78%, elevated transaminases in 83%,
      thrombocytopenia in 56%, and neurological involvement in 28%.
    supporting_text: >-
      Fever and rash were universal (100%); eschar was rare (6%).
      Gastrointestinal symptoms occurred in 44%, neurological involvement in
      28%, and arthralgia/myalgia in 33%. Laboratory abnormalities included
      thrombocytopenia (56%), hyponatremia (78%), elevated transaminases (83%),
      and markedly raised C-reactive protein.
- reference: PMID:7511715
  title: >-
    Rickettsia conorii infection of C3H/HeN mice. A model of
    endothelial-target rickettsiosis.
  findings:
  - statement: >-
      Intravenous R. conorii Malish 7 infection in C3H/HeN mice produces
      disseminated endothelial infection and vascular injury.
    supporting_text: >-
      Mice inoculated with a high dose of rickettsiae established disseminated
      endothelial infection on day 1, became ill with progressive increase in
      rickettsiae on day 4, and died with vascular injury-based
      meningoencephalitis and interstitial pneumonia on day 5 or 6.

classifications:
  harrisons_chapter:
  - classification_value: INFECTIOUS_DISEASES
    evidence:
    - reference: PMID:22628514
      reference_title: Genome sequence of Rickettsia conorii subsp. indica, the agent of Indian tick typhus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Rickettsia conorii subsp. indica is the agent of Indian tick typhus.
        The present study reports the draft genome of Rickettsia conorii subsp.
        indica strain ITTR (ATCC VR-597).
      explanation: >-
        The genome report identifies Indian tick typhus as an infection caused
        by a bacterial Rickettsia subspecies, placing it in Harrison's
        Infectious Diseases Part.

infectious_agent:
- name: Rickettsia conorii subsp. indica
  infectious_agent_term:
    preferred_term: Rickettsia conorii subsp. indica
    term:
      id: NCBITaxon:317865
      label: Rickettsia conorii subsp. indica
  description: >-
    Obligate intracellular spotted-fever-group rickettsial subspecies that
    causes Indian tick typhus.
  evidence:
  - reference: PMID:22628514
    reference_title: Genome sequence of Rickettsia conorii subsp. indica, the agent of Indian tick typhus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Rickettsia conorii subsp. indica is the agent of Indian tick typhus. The
      present study reports the draft genome of Rickettsia conorii subsp.
      indica strain ITTR (ATCC VR-597).
    explanation: >-
      The genome report names R. conorii subsp. indica strain ITTR as the
      etiologic agent of Indian tick typhus.
  - reference: PMID:15766388
    reference_title: >-
      Proposal to create subspecies of Rickettsia conorii based on multi-locus
      sequence typing and an emended description of Rickettsia conorii.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      We propose the names R. conorii subsp. conorii subsp. nov. (type strain =
      Malish, ATCC VR-613), R. conorii subspecies indica subsp. nov. (type
      strain = ATCC VR-597), R. conorii subspecies caspia subsp. nov. (type
      strain = A-167), and R. conorii subspecies israelensis subsp. nov. (type
      strain = ISTT CDC1).
    explanation: >-
      Multilocus taxonomic analysis formally places Indian tick typhus
      rickettsia inside R. conorii as subsp. indica.

transmission:
- name: Rhipicephalus tick bite inoculation
  description: >-
    Humans acquire Indian tick typhus when infected Rhipicephalus ticks bite
    and inoculate R. conorii subsp. indica into skin.
  evidence:
  - reference: PMID:15766388
    reference_title: >-
      Proposal to create subspecies of Rickettsia conorii based on multi-locus
      sequence typing and an emended description of Rickettsia conorii.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The characteristics are the same as those of the species. Transmitted to
      humans through the bite of Rhipicephalus sanguineus ticks.
    explanation: >-
      The taxonomic description of R. conorii subsp. indica records human
      transmission through bites of R. sanguineus ticks.
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PCR and sequencing of multiple rickettsial genes confirmed the presence
      of ITTR in both the patient and the tick. Furthermore, the genetic
      identity between these sequences provided evidence that R. turanicus can
      act as a vector of ITTR.
    explanation: >-
      Matching PCR sequences from a patient and an attached R. turanicus tick
      support a second Rhipicephalus vector for ITTR.

epidemiology:
- name: Indian-subcontinent Rhipicephalus tick exposure
  description: >-
    Indian tick typhus is tied to Rhipicephalus tick exposure in India and
    Pakistan, and ITTR has been molecularly detected farther east in Xinjiang.
  factors:
  - Indian subcontinent tick exposure
  - Rhipicephalus tick exposure
  evidence:
  - reference: PMID:15766388
    reference_title: >-
      Proposal to create subspecies of Rickettsia conorii based on multi-locus
      sequence typing and an emended description of Rickettsia conorii.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The type strain is Indian tick typhus, ATCC VR-597, which was isolated
      from a Rhipicephalus sanguineus tick collected in India by C.B. Philip in
      1950.
    explanation: >-
      The subspecies description ties the type Indian tick typhus isolate to an
      R. sanguineus tick from India.
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Rickettsia conorii Indian tick typhus strain (R. conorii subsp. indica,
      ITTR) was detected in both a human patient and an attached Rhipicephalus
      turanicus tick that was removed from the patient in Yanqi County,
      Xinjiang Uygur Autonomous Region (XUAR), China.
    explanation: >-
      The molecular case report extends documented ITTR infection and vector
      carriage to a patient and attached tick in Xinjiang.

pathophysiology:
- name: Rhipicephalus-Borne ITTR Inoculation
  role: trigger
  biological_scale: ORGANISM
  description: >-
    An infected Rhipicephalus tick bite introduces R. conorii subsp. indica into
    the dermis, seeding local rickettsial infection that can produce an
    inoculation eschar and then disseminate systemically.
  biological_processes:
  - preferred_term: inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  evidence:
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 55-year-old female farmer presented with fever, headache, eschar, and a
      maculopapular rash following a tick bite.
    explanation: >-
      The patient presentation directly connects tick exposure with the local
      eschar and systemic spotted-fever manifestations of ITTR infection.
  downstream:
  - target: Inoculation Eschar
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Local dermal rickettsial infection produces the necrotic eschar.
  - target: Sca2-Dependent Host-Cell Invasion
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Disseminating R. conorii cells engage endothelial invasion machinery.
  - target: Rickettsial Endothelial Infection
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Locally inoculated rickettsiae disseminate to vascular endothelium.

- name: Sca2-Dependent Host-Cell Invasion
  role: host_cell_invasion
  biological_scale: CELLULAR
  description: >-
    R. conorii uses the multifunctional Sca2 autotransporter during mammalian
    cell association and endothelial invasion, putting bacterial surface
    adhesins upstream of the intracellular endothelial infection that drives
    Indian tick typhus.
  cell_types:
  - preferred_term: endothelial cell of vascular tree
    term:
      id: CL:0002139
      label: endothelial cell of vascular tree
  biological_processes:
  - preferred_term: symbiont entry into host
    modifier: INCREASED
    term:
      id: GO:0044409
      label: symbiont entry into host
  evidence:
  - reference: PMID:22612237
    reference_title: >-
      Identification and characterization of the mammalian association and
      actin-nucleating domains in the Rickettsia conorii autotransporter
      protein, Sca2.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      A rickettsial autotransporter from Rickettsia conorii, Sca2, has been
      shown to be sufficient to mediate both adherence and invasion of human
      endothelial cells and to participate in intracellular actin-based
      motility.
    explanation: >-
      R. conorii Sca2 provides an experimentally characterized bacterial
      autotransporter that can mediate endothelial adhesion and invasion.
  downstream:
  - target: Arp2/3-Dependent Actin Remodeling
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Initial rickettsial contact triggers host actin assembly pathways needed
      for rickettsial uptake.

- name: Arp2/3-Dependent Actin Remodeling
  role: host_cytoskeletal_response
  biological_scale: CELLULAR
  description: >-
    Spotted-fever-group rickettsiae engage host Rho-family GTPase and WAVE
    signaling that converges on Arp2/3-mediated actin filament polymerization,
    remodeling the endothelial actin cortex during entry.
  cell_types:
  - preferred_term: endothelial cell of vascular tree
    term:
      id: CL:0002139
      label: endothelial cell of vascular tree
  biological_processes:
  - preferred_term: actin filament polymerization
    modifier: INCREASED
    term:
      id: GO:0030041
      label: actin filament polymerization
  evidence:
  - reference: PMID:22188208
    reference_title: >-
      Rickettsia parkeri invasion of diverse host cells involves an Arp2/3
      complex, WAVE complex and Rho-family GTPase-dependent pathway.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Receptor binding by Rickettsia proteins initiates activation of host
      protein tyrosine kinases, leading to Cdc42 activation and Rac-dependent
      activation of WAVE, which may act in parallel with other NPFs to activate
      Arp2/3. Finally, the Arp2/3 complex acts as the major nucleator of actin
      filaments during Rickettsia invasion of host cells.
    explanation: >-
      R. parkeri experiments define a conserved spotted-fever-group host actin
      program in which Rho-family GTPases and WAVE converge on Arp2/3 during
      mammalian-cell invasion.
  downstream:
  - target: Rickettsial Endothelial Infection
    causal_link_type: DIRECT
    description: >-
      Actin remodeling enables efficient endothelial uptake and cytosolic
      infection.

- name: Rickettsial Endothelial Infection
  role: cellular_infection
  description: >-
    R. conorii subsp. indica belongs to the spotted-fever rickettsiae whose
    pathogenic members invade and replicate in vascular endothelial cells,
    making microvascular endothelium the host-cell compartment that transduces
    infection into vasculitis.
  cell_types:
  - preferred_term: endothelial cell of vascular tree
    term:
      id: CL:0002139
      label: endothelial cell of vascular tree
  biological_processes:
  - preferred_term: biological process involved in interaction with host
    term:
      id: GO:0051701
      label: biological process involved in interaction with host
  evidence:
  - reference: PMID:19327117
    reference_title: Host-cell interactions with pathogenic Rickettsia species.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Although pathogenic Rickettsiae are able to infect and replicate in a
      number of different cell types in vitro, a unique property during in vivo
      infection is their affinity for vascular endothelial cells (ECs) lining
      small and medium-sized blood vessels in humans and in established animal
      models of infection
    explanation: >-
      The review identifies vascular endothelial cells as the in-vivo target
      that is shared by pathogenic spotted-fever rickettsiae.
  downstream:
  - target: Rickettsial Vasculitis
    causal_link_type: DIRECT
    description: Endothelial rickettsial infection drives vascular inflammation.

- name: Rickettsial Vasculitis
  role: vascular_response
  description: >-
    Endothelial rickettsial infection and inflammation produce small-vessel
    vasculitis, increased vascular permeability, and the fever, rash, and
    multisystem laboratory abnormalities of Indian tick typhus.
  cell_types:
  - preferred_term: endothelial cell of vascular tree
    term:
      id: CL:0002139
      label: endothelial cell of vascular tree
  biological_processes:
  - preferred_term: inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  - preferred_term: positive regulation of vascular permeability
    modifier: INCREASED
    term:
      id: GO:0043117
      label: positive regulation of vascular permeability
  evidence:
  - reference: PMID:34345128
    reference_title: Scrub Typhus and Other Rickettsial Infections.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The pathological hallmark of rickettsial infections is endothelial
      infection and inflammation causing vasculitis. Endothelial inflammation
      results in microvascular dysfunction and increased vascular permeability.
    explanation: >-
      The rickettsial critical-care review connects endothelial infection to
      vasculitis, microvascular dysfunction, and increased permeability.
  downstream:
  - target: Fever
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Systemic rickettsial inflammation produces fever.
  - target: Maculopapular Rash
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Cutaneous rickettsial vasculitis produces the exanthem.
  - target: Headache
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: The acute inflammatory syndrome can include headache.
  - target: Platelet Activation and Microthrombus Formation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      R. conorii endothelial injury can activate platelets and coagulation in
      the injured microvasculature.
  - target: Elevated Hepatic Transaminases
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Systemic rickettsial disease can injure the liver.
  - target: Hyponatremia
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Systemic rickettsial disease can include hyponatremia.
  - target: Neurologic Involvement
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: CNS vasculitis can produce neurological involvement.
  - target: Proteinuria
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Systemic rickettsial disease can involve the kidney.
  - target: Multifocal Retinitis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Rickettsial vascular inflammation can involve the retina.

- name: Platelet Activation and Microthrombus Formation
  role: consumptive_coagulation
  biological_scale: CELLULAR
  description: >-
    R. conorii endothelial injury is accompanied by TXA2-dependent platelet
    activation and thrombin generation in vivo, providing a consumptive route to
    thrombocytopenia and focal rickettsial microthrombi.
  cell_types:
  - preferred_term: platelet
    term:
      id: CL:0000233
      label: platelet
  biological_processes:
  - preferred_term: platelet activation
    modifier: INCREASED
    term:
      id: GO:0030168
      label: platelet activation
  - preferred_term: blood coagulation
    modifier: INCREASED
    term:
      id: GO:0007596
      label: blood coagulation
  evidence:
  - reference: PMID:8584998
    reference_title: >-
      Demonstration of Rickettsia Conorii-induced coagulative and platelet
      activation in vivo in patients with Mediterranean spotted fever.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our results provide biochemical evidence for the occurrence of
      TXA2-dependent platelet activation and thrombin generation in vivo,
      together with endothelial dysfunction. These phenomena could account for
      clinical manifestations of MSF, such as vasculitis and focal microthrombus
      formation.
    explanation: >-
      R. conorii Mediterranean spotted fever shares endothelial injury with
      Indian tick typhus and demonstrates the platelet/coagulation arm that can
      lower platelet counts during spotted-fever disease.
  downstream:
  - target: Thrombocytopenia
    causal_link_type: DIRECT
    description: Platelet activation and microthrombus formation consume platelets.

- name: Rickettsial Ribosomal Translation
  role: therapeutic_vulnerability
  conforms_to: "bacterial_protein_synthesis_inhibition#Bacterial mRNA Translation by the Ribosome"
  description: >-
    R. conorii subsp. indica, like other bacteria, depends on ribosomal
    translation of its mRNA, making the bacterial ribosome the conserved
    antibiotic target for doxycycline therapy.
  biological_processes:
  - preferred_term: Translation
    term:
      id: GO:0006412
      label: translation
  evidence:
  - reference: PMID:24336183
    reference_title: Ribosome-targeting antibiotics and mechanisms of bacterial resistance.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The ribosome is one of the main antibiotic targets in the bacterial cell.
    explanation: >-
      Review evidence establishes the bacterial ribosome as the conserved target
      class for tetracyclines such as doxycycline.

- name: Intracytosolic Rickettsia conorii Niche
  role: intrinsic_resistance
  conforms_to: "intracellular_pathogen_persistence#Intracellular Niche and Beta-Lactam Exclusion"
  description: >-
    Rickettsia species reside free in the host-cell cytosol and exploit host
    metabolites, so effective Indian tick typhus therapy must reach the
    intracellular bacterial compartment.
  biological_processes:
  - preferred_term: biological process involved in interaction with host
    term:
      id: GO:0051701
      label: biological process involved in interaction with host
  evidence:
  - reference: PMID:30148688
    reference_title: "Pathogenesis of Rickettsial Diseases: Pathogenic and Immune Mechanisms of an Endotheliotropic Infection."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Residing free in the cytosol of the host cell, they acquire many
      necessary components via transport mechanisms instead of maintaining genes
      for synthesizing sugars, lipids, nucleotides, and amino acids.
    explanation: >-
      The review supports the free cytosolic niche for pathogenic Rickettsia
      species, including the R. conorii complex.
  downstream:
  - target: Rickettsial Ribosomal Translation
    causal_link_type: DIRECT
    description: Intracytosolic R. conorii remains dependent on bacterial protein synthesis.

phenotypes:
- name: Fever
  category: Constitutional
  frequency: VERY_FREQUENT
  description: Fever is a core acute manifestation of Indian tick typhus.
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:41795239
    reference_title: >-
      The first pediatric cohort of Rickettsia conorii infection in Palestine: A
      five-year multicenter epidemiological and clinical analysis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Fever and rash were universal (100%);
    explanation: >-
      A PCR-confirmed pediatric R. conorii cohort reported fever in all cases,
      supporting the very-frequent fever band for the R. conorii complex.
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 55-year-old female farmer presented with fever, headache, eschar, and a
      maculopapular rash following a tick bite.
    explanation: >-
      Fever was part of the acute presentation in a PCR-confirmed ITTR
      infection.

- name: Headache
  category: Neurologic
  description: Headache can accompany acute ITTR infection.
  phenotype_term:
    preferred_term: Headache
    term:
      id: HP:0002315
      label: Headache
  evidence:
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 55-year-old female farmer presented with fever, headache, eschar, and a
      maculopapular rash following a tick bite.
    explanation: Headache was part of the acute PCR-confirmed ITTR presentation.

- name: Maculopapular Rash
  category: Dermatologic
  description: Indian tick typhus can produce a maculopapular rash.
  phenotype_term:
    preferred_term: Maculopapular exanthema
    term:
      id: HP:0040186
      label: Maculopapular exanthema
  evidence:
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 55-year-old female farmer presented with fever, headache, eschar, and a
      maculopapular rash following a tick bite.
    explanation: >-
      Maculopapular rash was present in the PCR-confirmed ITTR case.

- name: Inoculation Eschar
  category: Dermatologic
  description: >-
    Local necrosis at the infected tick bite can produce an inoculation eschar.
  phenotype_term:
    preferred_term: Eschar
    term:
      id: HP:6000793
      label: Eschar
  evidence:
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 55-year-old female farmer presented with fever, headache, eschar, and a
      maculopapular rash following a tick bite.
    explanation: Eschar was present after a tick bite in the PCR-confirmed ITTR case.

- name: Thrombocytopenia
  category: Hematologic
  frequency: FREQUENT
  description: Thrombocytopenia can accompany acute ITTR infection.
  phenotype_term:
    preferred_term: Thrombocytopenia
    term:
      id: HP:0001873
      label: Thrombocytopenia
  evidence:
  - reference: PMID:41795239
    reference_title: >-
      The first pediatric cohort of Rickettsia conorii infection in Palestine: A
      five-year multicenter epidemiological and clinical analysis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory abnormalities included thrombocytopenia (56%), hyponatremia
      (78%), elevated transaminases (83%), and markedly raised C-reactive
      protein.
    explanation: >-
      The pediatric R. conorii cohort places thrombocytopenia in the frequent
      range.
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory findings indicated thrombocytopenia, liver enzyme elevation,
      and proteinuria, which, combined with clinical symptoms, strongly
      suggested a rickettsial infection.
    explanation: >-
      Thrombocytopenia was documented as a laboratory abnormality in a
      PCR-confirmed ITTR infection.

- name: Elevated Hepatic Transaminases
  category: Digestive System
  frequency: VERY_FREQUENT
  description: Hepatic enzyme elevation can accompany acute ITTR infection.
  phenotype_term:
    preferred_term: Elevated hepatic transaminase
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  evidence:
  - reference: PMID:41795239
    reference_title: >-
      The first pediatric cohort of Rickettsia conorii infection in Palestine: A
      five-year multicenter epidemiological and clinical analysis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory abnormalities included thrombocytopenia (56%), hyponatremia
      (78%), elevated transaminases (83%), and markedly raised C-reactive
      protein.
    explanation: >-
      The pediatric R. conorii cohort places elevated transaminases in the
      very-frequent range.
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory findings indicated thrombocytopenia, liver enzyme elevation,
      and proteinuria, which, combined with clinical symptoms, strongly
      suggested a rickettsial infection.
    explanation: >-
      Liver enzyme elevation in the ITTR case supports a transaminase phenotype.

- name: Hyponatremia
  category: Endocrine
  frequency: FREQUENT
  description: Hyponatremia can accompany acute R. conorii infection.
  phenotype_term:
    preferred_term: Hyponatremia
    term:
      id: HP:0002902
      label: Hyponatremia
  evidence:
  - reference: PMID:41795239
    reference_title: >-
      The first pediatric cohort of Rickettsia conorii infection in Palestine: A
      five-year multicenter epidemiological and clinical analysis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory abnormalities included thrombocytopenia (56%), hyponatremia
      (78%), elevated transaminases (83%), and markedly raised C-reactive
      protein.
    explanation: >-
      The pediatric R. conorii cohort reported hyponatremia in the frequent
      range.

- name: Neurologic Involvement
  category: Neurologic
  frequency: OCCASIONAL
  description: Neurologic involvement can accompany acute R. conorii infection.
  phenotype_term:
    preferred_term: Neurological involvement
    term:
      id: HP:0000707
      label: Abnormality of the nervous system
    coarse_binding_basis: SOURCE_UNSPECIFIED
  evidence:
  - reference: PMID:41795239
    reference_title: >-
      The first pediatric cohort of Rickettsia conorii infection in Palestine: A
      five-year multicenter epidemiological and clinical analysis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Gastrointestinal symptoms occurred in 44%, neurological involvement in
      28%, and arthralgia/myalgia in 33%.
    explanation: >-
      The pediatric R. conorii cohort reported neurologic involvement in the
      occasional range.

- name: Proteinuria
  category: Genitourinary
  description: Proteinuria can accompany acute ITTR infection.
  phenotype_term:
    preferred_term: Proteinuria
    term:
      id: HP:0000093
      label: Proteinuria
  evidence:
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory findings indicated thrombocytopenia, liver enzyme elevation,
      and proteinuria, which, combined with clinical symptoms, strongly
      suggested a rickettsial infection.
    explanation: >-
      Proteinuria was documented as a renal laboratory abnormality in the
      PCR-confirmed ITTR infection.

- name: Multifocal Retinitis
  category: Ophthalmic
  description: >-
    Multifocal retinitis can follow serologically proven Indian tick typhus in
    South Indian patients.
  phenotype_term:
    preferred_term: Retinitis
    term:
      id: HP:0032118
      label: Retinitis
  evidence:
  - reference: PMID:30451192
    reference_title: Ocular manifestations of Rickettsia conorii in South India.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Examination showed multifocal retinitis; mostly bilateral; patients had a
      history of fever approximately 4 weeks prior to onset of symptoms.
    explanation: >-
      A South Indian cluster of serologically proven Indian tick typhus cases
      established multifocal retinitis as an ocular manifestation.

diagnosis:
- name: Rickettsial PCR and gene sequencing
  description: >-
    PCR amplification and sequencing of rickettsial genes can confirm acute
    ITTR infection and match the pathogen sequence between patient material and
    the attached tick.
  diagnosis_term:
    preferred_term: polymerase chain reaction
    term:
      id: NCIT:C17003
      label: Polymerase Chain Reaction
  results: Positive rickettsial PCR with sequence identity to ITTR confirms infection.
  evidence:
  - reference: PMID:41650674
    reference_title: >-
      Identification of Rickettsia conorii Indian tick typhus strain in a
      Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PCR and sequencing of multiple rickettsial genes confirmed the presence
      of ITTR in both the patient and the tick.
    explanation: >-
      PCR followed by sequencing confirmed ITTR in an acutely infected patient.

- name: Indirect immunofluorescence assay serology
  description: >-
    Indirect immunofluorescence can support spotted-fever-group rickettsiosis
    serodiagnosis, but serology may be retrospective because early false
    negatives occur before delayed seroconversion.
  results: >-
    IgG or IgM seroreactivity, especially seroconversion or a rising titer,
    supports recent spotted-fever-group rickettsial infection.
  evidence:
  - reference: PMID:42390463
    reference_title: >-
      Diagnostic challenges in re-emerging rickettsioses: why current tools
      fall short.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      the Weil-Felix test lacks necessary specificity, while the gold standard
      indirect immunofluorescence assay (IFA) is primarily retrospective due to
      delayed seroconversion.
    explanation: >-
      The rickettsial diagnostics review identifies IFA as the serologic gold
      standard and explains why acute-phase serology can lag behind illness.

treatments:
- name: Empiric doxycycline
  description: >-
    Doxycycline is first-line empiric therapy for suspected Indian tick typhus
    and related rickettsial diseases because it blocks rickettsial ribosomal
    translation in the intracellular bacterial compartment.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: doxycycline
      term:
        id: CHEBI:50845
        label: doxycycline
  target_mechanisms:
  - target: Rickettsial Ribosomal Translation
    treatment_effect: INHIBITS
    description: >-
      Doxycycline inhibits bacterial protein synthesis through the conserved
      tetracycline-class ribosomal target.
  - target: Intracytosolic Rickettsia conorii Niche
    treatment_effect: BYPASSES
    description: >-
      Doxycycline can reach the R. conorii cytosolic compartment inside host
      cells.
  evidence:
  - reference: PMID:28361787
    reference_title: IAP Guidelines on Rickettsial Diseases in Children.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Indian tick typhus and scrub typhus are commonly seen rickettsial
      diseases in India. It is recommended that practicing pediatricians should
      be well conversant with compatible clinical scenario, suggestive
      epidemiological features, differential diagnoses and suggestive laboratory
      features to make diagnosis and avoid over diagnosis of these infections,
      as suggested in these guidelines. Doxycycline is the drug of choice and
      treatment should begin promptly without waiting for confirmatory
      laboratory results.
    explanation: >-
      Indian pediatric rickettsial guidelines identify doxycycline as the drug
      of choice and recommend prompt empiric therapy for diseases that include
      Indian tick typhus.

- name: Azithromycin
  description: >-
    Azithromycin is a macrolide alternative for spotted-fever-group
    rickettsioses when doxycycline cannot be used or is unavailable.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: azithromycin
      term:
        id: CHEBI:2955
        label: azithromycin
  target_mechanisms:
  - target: Rickettsial Ribosomal Translation
    treatment_effect: INHIBITS
    description: >-
      Azithromycin targets bacterial ribosomal translation through a macrolide
      mechanism.
  evidence:
  - reference: PMID:34345128
    reference_title: Scrub Typhus and Other Rickettsial Infections.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Intravenous doxycycline with a loading dose is the most widely used
      antibiotic in critically ill patients, with azithromycin as a suitable
      alternative.
    explanation: >-
      The rickettsial critical-care review identifies azithromycin as a
      suitable alternative to doxycycline for serious rickettsial infection.

animal_models:
- name: C3H/HeN Rickettsia conorii Malish infection mouse
  species: Mouse
  genotype: Wild-type C3H/HeN
  publication: PMID:7511715
  description: >-
    Intravenous R. conorii Malish 7 infection in C3H/HeN mice produces
    disseminated endothelial infection, illness, and dose-dependent
    vascular-injury outcomes, modeling the endotheliotropic vasculitis shared
    across R. conorii spotted-fever infections.
  modeled_mechanisms:
  - target: Rickettsial Endothelial Infection
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      High-dose infection establishes disseminated endothelial infection and
      vascular-injury-based meningoencephalitis and interstitial pneumonia; the
      low-dose infection produces reversible illness with rickettsial clearance
      and lymphohistiocytic perivasculitis.
    limitations: >-
      The model uses the R. conorii Malish 7 strain associated with
      Mediterranean spotted fever, not R. conorii subsp. indica, so it supports
      the shared endotheliotropic rickettsial mechanism rather than an
      indica-specific virulence program.
    evidence:
    - reference: PMID:7511715
      reference_title: >-
        Rickettsia conorii infection of C3H/HeN mice. A model of
        endothelial-target rickettsiosis.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Mice inoculated with a high dose of rickettsiae established
        disseminated endothelial infection on day 1, became ill with
        progressive increase in rickettsiae on day 4, and died with vascular
        injury-based meningoencephalitis and interstitial pneumonia on day 5 or
        6. Mice inoculated with the low rickettsial dose became ill on day 5
        and recovered by day 10.
      explanation: >-
        The dose-stratified C3H/HeN model directly measures the endothelial
        infection and vascular-injury phenotypes central to spotted-fever
        pathogenesis.
  evidence:
  - reference: PMID:7511715
    reference_title: >-
      Rickettsia conorii infection of C3H/HeN mice. A model of
      endothelial-target rickettsiosis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      This experimental infection provides the best available model for
      rickettsial disease with endothelial infection and injury, immune
      rickettsial clearance, regeneration of endothelium, and repair of the
      vascular lesions.
    explanation: >-
      The authors frame C3H/HeN R. conorii infection as an endothelial-target
      rickettsiosis model.
📚

References & Deep Research

References

8
PMID:22628514
Genome sequence of Rickettsia conorii subsp. indica, the agent of Indian tick typhus.
1 finding
Rickettsia conorii subsp. indica strain ITTR is the agent of Indian tick typhus.
"Rickettsia conorii subsp. indica is the agent of Indian tick typhus. The present study reports the draft genome of Rickettsia conorii subsp. indica strain ITTR (ATCC VR-597)."
PMID:15766388
Proposal to create subspecies of Rickettsia conorii based on multi-locus sequence typing and an emended description of Rickettsia conorii.
1 finding
The ITTR strain is taxonomically R. conorii subsp. indica, a genotypic and serotypically distinct R. conorii subspecies transmitted through Rhipicephalus sanguineus tick bite.
"The characteristics are the same as those of the species. Transmitted to humans through the bite of Rhipicephalus sanguineus ticks."
PMID:41650674
Identification of Rickettsia conorii Indian tick typhus strain in a Patient and an Attached Rhipicephalus turanicus Tick in Xinjiang, China.
1 finding
PCR and sequencing confirmed R. conorii Indian tick typhus strain in both an acutely ill patient and an attached Rhipicephalus turanicus tick.
"PCR and sequencing of multiple rickettsial genes confirmed the presence of ITTR in both the patient and the tick."
PMID:22612237
Identification and characterization of the mammalian association and actin-nucleating domains in the Rickettsia conorii autotransporter protein, Sca2.
1 finding
R. conorii Sca2 is sufficient to mediate adherence and invasion of human endothelial cells and participates in intracellular actin-based motility.
"A rickettsial autotransporter from Rickettsia conorii, Sca2, has been shown to be sufficient to mediate both adherence and invasion of human endothelial cells and to participate in intracellular actin-based motility."
PMID:22188208
Rickettsia parkeri invasion of diverse host cells involves an Arp2/3 complex, WAVE complex and Rho-family GTPase-dependent pathway.
1 finding
Host Rho-family GTPase and WAVE signaling converge on the Arp2/3 complex as the major actin nucleator during Rickettsia invasion of host cells.
"Receptor binding by Rickettsia proteins initiates activation of host protein tyrosine kinases, leading to Cdc42 activation and Rac-dependent activation of WAVE, which may act in parallel with other NPFs to activate Arp2/3. Finally, the Arp2/3 complex acts as the major nucleator of actin..."
PMID:8584998
Demonstration of Rickettsia Conorii-induced coagulative and platelet activation in vivo in patients with Mediterranean spotted fever.
1 finding
Acute R. conorii infection is associated with TXA2-dependent platelet activation, thrombin generation, endothelial dysfunction, vasculitis, and focal microthrombus formation.
"Our results provide biochemical evidence for the occurrence of TXA2-dependent platelet activation and thrombin generation in vivo, together with endothelial dysfunction. These phenomena could account for clinical manifestations of MSF, such as vasculitis and focal microthrombus formation."
PMID:41795239
The first pediatric cohort of Rickettsia conorii infection in Palestine: A five-year multicenter epidemiological and clinical analysis.
1 finding
A PCR-confirmed pediatric R. conorii cohort documented universal fever and rash, hyponatremia in 78%, elevated transaminases in 83%, thrombocytopenia in 56%, and neurological involvement in 28%.
"Fever and rash were universal (100%); eschar was rare (6%). Gastrointestinal symptoms occurred in 44%, neurological involvement in 28%, and arthralgia/myalgia in 33%. Laboratory abnormalities included thrombocytopenia (56%), hyponatremia (78%), elevated transaminases (83%), and markedly raised..."
PMID:7511715
Rickettsia conorii infection of C3H/HeN mice. A model of endothelial-target rickettsiosis.
1 finding
Intravenous R. conorii Malish 7 infection in C3H/HeN mice produces disseminated endothelial infection and vascular injury.
"Mice inoculated with a high dose of rickettsiae established disseminated endothelial infection on day 1, became ill with progressive increase in rickettsiae on day 4, and died with vascular injury-based meningoencephalitis and interstitial pneumonia on day 5 or 6."

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create Indian tick typhus · 2026-09-28T06:16:47Z · View source

Created a de novo Indian tick typhus entry from the OpenScientist deep-research report, with Rickettsia conorii subsp. indica identity, Rhipicephalus transmission, Sca2/Arp2/3-to-endothelium invasion biology, TXA2-dependent platelet activation and microthrombus formation, cohort-backed R. conorii phenotypes, PCR and IFA diagnostics, doxycycline and azithromycin treatments, and a C3H/HeN R. conorii Malish infection mouse model. Broadened the cohort-backed neurologic phenotype from Infectious Encephalitis to SOURCE_UNSPECIFIED Neurologic Involvement because the evidence reports neurological involvement without naming encephalitis.

OpenScientist ▸
Indian Tick Typhus (MONDO:0000229): A Comprehensive Disease Characterization
openscientist-autonomous 37 citations 2026-09-27T23:05:55.971601

Indian Tick Typhus (MONDO:0000229): A Comprehensive Disease Characterization

Summary

Indian tick typhus (ITT) is an acute, tick-borne bacterial zoonosis and a member of the spotted fever group (SFG) rickettsioses. It is caused by Rickettsia conorii subsp. indica (reference strain ITTR, ATCC VR-597), an obligate intracellular Gram-negative coccobacillus, and is transmitted to humans through the bite of the brown dog tick, Rhipicephalus sanguineus PMID: 22628514; PMID: 32997473. It is one of four genotypic subspecies within R. conorii — alongside the Malish/Mediterranean spotted fever (MSF) strain, Astrakhan fever, and Israeli spotted fever — which are >98% identical at the nucleotide level yet serotypically distinct PMID: 15766388. Because ITT is clinically, mechanistically, and therapeutically part of the R. conorii/MSF continuum, much of the mechanistic and clinical evidence base is shared across these subspecies.

The core pathophysiology is a systemic small-vessel vasculitis: the bacterium adheres to and invades vascular endothelial cells using surface cell antigen (Sca) autotransporter proteins and hijacks the host Arp2/3 actin-nucleation machinery for entry and intracellular actin-based motility PMID: 22612237; PMID: 22188208. Endothelial infection triggers inflammation, platelet and coagulation activation, and increased vascular permeability, producing the classic clinical triad of fever, an inoculation eschar (tache noire), and a maculopapular rash PMID: 34345128; PMID: 8584998. Disease is usually mild-to-moderate and self-limited, but severe "malignant" forms — strongly age-dependent — cause meningoencephalitis, hemophagocytic lymphohistiocytosis (HLH), purpura fulminans, and multi-organ failure PMID: 32997473; PMID: 30972588.

Diagnosis rests on serology (indirect immunofluorescence assay [IFA] is the gold standard, Weil–Felix is nonspecific) and, increasingly, species-specific PCR of the gltA and ompA genes. Doxycycline is the unequivocal treatment of choice, producing rapid defervescence and excellent outcomes; there is no human genetic etiology and no licensed vaccine, so prevention depends on personal protection against tick bites and control of brown dog ticks on dogs and in the environment PMID: 42390463; PMID: 30150470; PMID: 15109588. This report is compiled from aggregated disease-level resources and primary literature, not from individual EHR records. Because ITT is caused by an intracellular bacterium, several template sections designed for genetic/Mendelian disorders (causal human genes, pathogenic variants, inheritance patterns) are not applicable and are explicitly marked as such.

Section 1 — Disease Information

Overview. Indian tick typhus is an acute febrile illness caused by Rickettsia conorii subsp. indica, an obligate intracellular member of the spotted fever group of the genus Rickettsia. It is the principal SFG rickettsiosis of the Indian subcontinent and presents as fever with an inoculation eschar and maculopapular rash following a tick bite PMID: 30451192; PMID: 41650674.

Key identifiers:

Resource Identifier
MONDO MONDO:0000229
ICD-10 A77.1 (Spotted fever due to Rickettsia conorii)
ICD-11 1C30.0 (Spotted fever group rickettsiosis)
MeSH Boutonneuse Fever (D001907) — MSF/R. conorii group
NCBI Taxonomy (pathogen) Rickettsia conorii subsp. indica
Reference strain ITTR, ATCC VR-597

Synonyms / alternative names: Indian tick typhus; Rickettsia conorii subsp. indica infection; Indian tick typhus rickettsiosis (ITTR). It sits within the broader Mediterranean spotted fever / boutonneuse fever complex and the SFG rickettsioses.

Source of information: Aggregated disease-level literature and reference microbiology resources — not individual EHR data.

Section 2 — Etiology

Primary cause (infectious). ITT is caused by R. conorii subsp. indica strain ITTR (ATCC VR-597), the etiologic agent identified by genome sequencing PMID: 22628514. It is one of four multi-locus sequence typing (MLST) genotypes within R. conorii, sharing 98.2–100% pairwise nucleotide similarity across 16S rRNA, gltA, ompA, ompB, and sca4 with the Malish (MSF), Astrakhan fever, and Israeli spotted fever genotypes, yet remaining serotypically distinct PMID: 15766388. The vector is the brown dog tick Rhipicephalus sanguineus; ITTR has also been detected in Rhipicephalus turanicus removed from a patient PMID: 41650674.

Risk factors — environmental/behavioral. The dominant risk factor is tick exposure. In a military cohort, the primary risk factor for confirmed/probable SFG disease was finding >10 ticks on the body PMID: 12653142. Occupational and recreational contact with dogs and tick habitats, warm-season (summer) exposure, and residence in or travel to endemic areas increase risk PMID: 40608626; PMID: 41795239. Advanced age is the strongest risk factor for severe disease (see Section 11).

Risk factors — genetic. No human host genetic susceptibility variants have been established for ITT; this is an environmentally/behaviorally driven infectious disease. (Not applicable — no human causal or susceptibility loci identified.)

Protective factors. Behavioral: doxycycline use and rolling up long sleeves were protective against seropositivity in an exposed cohort PMID: 12653142; tick repellents, permethrin-treated clothing, and frequent tick checks reduce exposure PMID: 33549976. No genetic protective variants are described. (Genetic protective factors not applicable.)

Gene–environment interactions. Not applicable — no human genotype × exposure interactions have been characterized for this infectious disease.

Section 3 — Phenotypes

The clinical phenotype is a systemic febrile vasculitic illness. Key manifestations, with suggested HPO terms:

Phenotype Type Frequency / notes HPO suggestion
Fever Symptom ~100% (universal) HP:0001945 Fever
Maculopapular rash (incl. palms/soles) Clinical sign ~100% in pediatric cohorts; may involve palms and soles HP:0000988 Skin rash
Inoculation eschar (tache noire) Clinical sign ~74–77% in adult MSF; rare (6%) in some pediatric cohorts HP:0200041 (cutaneous ulcer/eschar)
Headache Symptom Common HP:0002315 Headache
Thrombocytopenia Lab abnormality ~56% HP:0001873 Thrombocytopenia
Elevated transaminases Lab abnormality ~83% HP:0002910 Elevated hepatic transaminase
Proteinuria Lab abnormality Reported HP:0000093 Proteinuria
Hyponatremia Lab abnormality ~78% (pediatric) HP:0002902 Hyponatremia
Meningoencephalitis Clinical sign (severe) ~28% neurological involvement (pediatric); rare severe HP:0002383 Encephalitis
Hemophagocytic lymphohistiocytosis Lab/clinical (severe) Rare; fatal case, H-score 224 HLH-associated
Retinitis (bilateral multifocal) Clinical sign (severe) Rare; ~4 weeks post-fever Retinitis (HP:0000602-adjacent)
Peripheral gangrene / purpura fulminans Clinical sign (severe) Rare HP:0100758 Gangrene

The classic triad is fever + eschar/rash + multisystem involvement PMID: 34345128. A representative adult presentation: "A 55-year-old female farmer presented with fever, headache, eschar, and a maculopapular rash following a tick bite. Laboratory findings indicated thrombocytopenia, liver enzyme elevation, and proteinuria" PMID: 41650674.

Onset, severity, progression, frequency. Onset is acute, typically after an incubation of several days following a tick bite. Rash usually appears on days 3–6 but may be delayed to day 8 in atypical cases PMID: 29331008. Severity is variable — most cases are mild and self-limited; a minority progress to severe multi-organ disease. Progression is acute/monophasic with recovery on treatment.

Quality-of-life impact. In uncomplicated, promptly treated disease, QoL impact is short-lived (hospital stay ~5 days, full recovery) PMID: 41795239. Severe forms cause lasting disability: e.g., a 14-month-old with meningoencephalitis had persistent neurological sequelae including decreased vision and epileptic seizures PMID: 20797742, and amputation was required in one case of symmetric peripheral gangrene PMID: 29169658. No formal EQ-5D/SF-36 data are available for ITT specifically.

Section 4 — Genetic/Molecular Information

This section is largely NOT APPLICABLE in the Mendelian sense: ITT is an infectious disease with no causal human genes, no pathogenic human germline/somatic variants, no modifier genes, and no chromosomal abnormalities. There is no human inheritance.

The relevant "genetics" are those of the pathogen genome:

  • R. conorii has a small, reductive genome (~1.27 Mb, ~1,374 genes) with the fewest pseudogenes among rickettsiae and 560 unique genes PMID: 16481486.
  • All Rickettsia lack enzymes for sugar metabolism, lipid biosynthesis, nucleotide synthesis, and amino acid metabolism, depending on the host for nutrition and building blocks; they retain a complete TCA cycle, multiple ATP/ADP translocase genes (to import host ATP), and a type IV secretion system PMID: 16481486.
  • Key pathogen loci: sca2 (adhesin/invasin/actin motility), ompA and ompB (Sca5/Sca0 outer membrane proteins; also diagnostic targets), sca4, gltA (citrate synthase; diagnostic target), and rickA (actin polymerization, unique to SFG) PMID: 22612237; PMID: 16481486.
  • Virulence in Rickettsia is largely associated with genome reduction / loss of regulatory genes PMID: 19379498, and ~80% of R. conorii "orphan" ORFs are short gene fragments reflecting ongoing genome decay PMID: 12832625.

Epigenetics / host molecular profiling: No host DNA-methylation, histone-modification, or large-scale transcriptomic/proteomic/metabolomic disease signatures specific to ITT have been established beyond selective modulation of host antioxidant enzymes (Section 6).

Section 5 — Environmental Information

Infectious agent: Rickettsia conorii subsp. indica (SFG rickettsia; obligate intracellular Gram-negative coccobacillus) PMID: 22628514.

Environmental / ecological factors: The disease is defined by an arthropod-borne transmission ecology. The vector-and-reservoir is the brown dog tick R. sanguineus (with transovarial and transstadial maintenance characteristic of SFG rickettsiae), and dogs/companion animals amplify circulation PMID: 32997473; PMID: 40871278. Warm seasons and tick-dense habitats increase exposure.

Lifestyle factors: Outdoor/occupational activity (farming, military, recreation) in endemic areas and dog contact are the principal behavioral determinants PMID: 12653142; PMID: 41650674. Classic toxic/pollution/radiation exposures are not relevant.

Section 6 — Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

  1. An infected R. sanguineus tick bites the human host and inoculates R. conorii subsp. indica into the dermis — leads to local infection at the bite site (forming the eschar/tache noire).
  2. Rickettsial Sca2 autotransporter (with OmpA/OmpB adhesins) mediates adherence to and invasion of vascular endothelial cells — results in intracellular infection PMID: 22612237.
  3. Invasion converges on the host Arp2/3 complex (with Rac GTPases and the WAVE nucleation-promoting complex), which nucleates actin to drive bacterial entry — leads to cytosolic access PMID: 22188208.
  4. Once cytosolic, Sca2 and RickA nucleate actin for intracellular actin-based motility, enabling cell-to-cell spread — results in dissemination through the endothelium PMID: 22612237; PMID: 16481486.
  5. Endothelial infection triggers endothelial inflammation and injury (vasculitis) — leads to microvascular dysfunction PMID: 34345128.
  6. Branch A (coagulation): Endothelial injury drives TXA2-dependent platelet activation and thrombin generation — results in focal microthrombus formation PMID: 8584998.
  7. Branch B (permeability): Endothelial dysfunction (raised endothelin-1) increases vascular permeability — results in edema, rash, and, when severe, multi-organ failure PMID: 34345128; PMID: 8584998.
  8. Branch C (autoimmunity, inferred): Endothelial membrane damage elicits antiphospholipid antibodies, which may contribute to microthrombi (mechanistic role inferred, not proven) PMID: 8679900.
  9. Systemic small-vessel vasculitis in skin, brain, lung, liver, kidney, and eye — leads to the multi-organ clinical phenotype (fever, rash, eschar, and, in severe cases, meningoencephalitis, HLH, gangrene, renal failure) PMID: 34345128; PMID: 7511715.
  10. Protective immunity requires CD8 T lymphocytes to clear rickettsiae from endothelial cells; failure of this response — leads to persistent/lethal infection PMID: 9164951.

Detail by category

Molecular pathways / cellular processes. Host actin-cytoskeleton remodeling via the Arp2/3 complex, WAVE2, and Rho-family GTPases (Rac1/Rac2) drives invasion; an RNAi screen identified 21 core host proteins required PMID: 22188208. Downstream cellular processes are endothelial inflammation/activation, platelet activation, coagulation, and increased permeability (GO suggestions: GO:0002544 chronic inflammatory response; GO:0007596 blood coagulation; GO:0030041 actin filament polymerization; GO:0050900 leukocyte migration).

Protein dysfunction. Pathogen surface autotransporters Sca2, OmpA (Sca5), OmpB (Sca0) mediate host-cell association; Sca2 has separable mammalian-association and actin-nucleation domains — pre-incubation with the mammalian-association region competitively inhibits invasion PMID: 22612237.

Metabolic changes. The pathogen imports host ATP via ATP/ADP translocases and lacks biosynthetic pathways PMID: 16481486. In the host, antioxidant/oxidative-stress enzymes (glutathione peroxidase/reductase, SOD, G6PD) are selectively modulated in infected tissues, most in the lungs PMID: 15120155 — evidence for oxidative stress as a tissue-damage mechanism.

Immune involvement. Protective clearance is CD8 T-cell dependent: CD8-depleted (but not CD4-depleted) mice die or remain persistently infected, and adoptive transfer of immune CD4 or CD8 cells protects PMID: 9164951. Cell types (CL suggestions): endothelial cell (CL:0000115); CD8-positive T cell (CL:0000625); platelet (CL:0000233); Kupffer cell / macrophage (CL:0000091).

Tissue damage mechanisms. Vasculitis-driven microvascular injury, microthrombosis/ischemia, oxidative stress, and increased permeability PMID: 34345128; PMID: 8584998; PMID: 15120155.

Section 7 — Anatomical Structures Affected

Because the primary target is vascular endothelium (UBERON:0002139 endothelium; UBERON:0001981 blood vessel), disease is systemic and multi-organ.

Organ / system Involvement UBERON Evidence
Skin Rash, eschar/tache noire UBERON:0002097 PMID: 40608626
Brain / CNS Meningoencephalitis, cerebral infarction UBERON:0000955 PMID: 20797742; PMID: 28491211; PMID: 35263931
Lung Interstitial pneumonia/infiltrates UBERON:0002048 PMID: 7511715; PMID: 30972588
Liver Transaminitis, hepatic granulomas (Kupffer cell/hepatocyte infection) UBERON:0002107 PMID: 7511715; PMID: 41650674
Kidney Proteinuria, acute tubular necrosis/renal failure UBERON:0002113 PMID: 41650674; PMID: 28292166
Eye Bilateral multifocal retinitis retina UBERON:0000966 PMID: 30451192
Blood / marrow Thrombocytopenia, HLH UBERON:0000178 PMID: 40693676; PMID: 41650674

Body systems: cardiovascular (small vessels), nervous, respiratory, hepatobiliary/digestive, urinary, hematologic, and ophthalmic. Tissue/cell level: vascular endothelial cells (CL:0000115) are the primary target; Kupffer cells/macrophages and hepatocytes are infected in the liver PMID: 7511715. Subcellular: the bacterium resides free in the host cytosol (GO:0005829 cytosol) and manipulates the actin cytoskeleton (GO:0015629). Lateralization: manifestations are generally bilateral/systemic (e.g., bilateral multifocal retinitis; bilateral asymmetric brain lesions on MRI) PMID: 30451192; PMID: 35263931.

Section 8 — Temporal Development

Onset: Acute, affecting all age groups (children through elderly) PMID: 32997473. Symptoms begin days after a tick bite; rash typically emerges on days 3–6 (occasionally delayed to day 8) PMID: 29331008.

Progression / course: Predominantly acute, monophasic, and self-limited. With prompt doxycycline, fever resolves within ~2–2.5 days and patients recover fully in days PMID: 30150470; PMID: 41795239. A minority progress rapidly to severe "malignant" multi-organ disease PMID: 32997473.

Duration / remission: Self-limited/treatment-resolved; not chronic or relapsing. There is no established latent or recurrent phase.

Critical period for intervention: The acute phase, when doxycycline is most effective — early empirical therapy (before serologic confirmation) is the key intervention window PMID: 42390463; PMID: 28361787.

Section 9 — Inheritance and Population

Inheritance: Not applicable — infectious, non-heritable. No inheritance pattern, penetrance, expressivity, anticipation, mosaicism, founder effect, consanguinity, or carrier frequency applies.

Epidemiology. In a 10-year Bulgarian cohort of 549 MSF patients, incidence reached 9.44/100,000; tache noire was present in ~74–77% PMID: 32997473. Rickettsial diseases contribute 25–50% of acute undifferentiated febrile illnesses in endemic regions PMID: 42390463; PMID: 34345128. In India, only limited serologically proven outbreaks of ITT specifically have been reported, and it is likely underdiagnosed PMID: 30451192.

Geographic distribution: Endemic to the Indian subcontinent for the indica subspecies; the broader R. conorii/MSF complex is endemic across the Mediterranean basin, Africa, the Middle East, and parts of Asia PMID: 15766388; PMID: 40608626. Cases cluster in summer/warm seasons PMID: 41795239.

Demographics / sex / age: All ages are affected; pediatric cohorts show slight male predominance (e.g., 56% male) PMID: 41795239. Age is the dominant demographic determinant of severity, with severe disease more frequent in those >65 years (26.4% vs 10.5%; p=0.002) PMID: 30972588.

Section 10 — Diagnostics

Serology (mainstay): IFA is the gold standard but is largely retrospective due to delayed seroconversion; the Weil–Felix test lacks specificity; false negatives occur early PMID: 42390463; PMID: 34345128. Seroconversion is often documented only in convalescent samples PMID: 30522428.

Molecular (PCR): Multiplex/real-time PCR enables early, species-specific identification during the acute phase; species confirmation is by PCR and DNA sequencing of the gltA and ompA genes, often from eschar/skin biopsy PMID: 42390463; PMID: 40608626; PMID: 30522428.

Laboratory findings (supportive): thrombocytopenia, elevated transaminases, proteinuria, hyponatremia, raised CRP PMID: 41650674; PMID: 41795239. Imaging: MRI shows multifocal bilateral T2/FLAIR hyperintensities with diffusion restriction in meningoencephalitis PMID: 35263931.

Genetic/omics testing (host): Not applicable — no human genetic testing is used to diagnose this infectious disease. The relevant "genetic testing" is pathogen genotyping (gltA/ompA sequencing).

Clinical criteria & differential diagnosis: Diagnosis is clinical-epidemiological (fever + rash involving palms/soles + eschar after tick exposure) supported by serology/PCR PMID: 40608626. Differentials: dengue, malaria, leptospirosis, scrub typhus, measles, and other causes of acute undifferentiated febrile illness PMID: 42390463; PMID: 42658412.

Section 11 — Outcome/Prognosis

Overall prognosis is excellent with prompt treatment. In a prospective cohort, single-day doxycycline produced uneventful recovery in all patients, with fever clearing 2.55 ± 1.14 days after treatment; 11.4% had severe disease PMID: 30150470. A pediatric cohort reported rapid defervescence and full recovery with no deaths or severe complications PMID: 41795239.

Severity and mortality. MSF/R. conorii is historically benign but includes severe "malignant" forms with fatal outcomes strongly influenced by patient age PMID: 32997473. Severe disease is more frequent in the elderly (26.4% vs 10.5%; p=0.002) PMID: 30972588. A purpura fulminans case series (including SFG rickettsioses) reported 18.2% overall mortality PMID: 32998655.

Complications: meningoencephalitis with neurological sequelae (decreased vision, epilepsy) PMID: 20797742; cerebral infarction/stroke PMID: 28491211; HLH (fatal case, H-score 224) PMID: 40693676; symmetric peripheral gangrene requiring amputation PMID: 29169658; acute tubular necrosis and fatal multivisceral failure with late diagnosis PMID: 28292166; and rickettsial retinitis PMID: 30451192.

Prognostic factors: advanced age, diagnostic/treatment delay, and severe multi-organ involvement predict poor outcome; timely doxycycline is the strongest modifiable predictor of good outcome PMID: 32997473; PMID: 28292166.

Section 12 — Treatment

First-line pharmacotherapy: Doxycycline (tetracycline-class; NCIT: C305 Doxycycline). It is the drug of choice, halting bacterial replication and producing rapid clinical response PMID: 34345128; PMID: 28361787. Regimens include short-course oral therapy (even single-day, two 200 mg doses) with uneventful recovery PMID: 30150470, and IV doxycycline with a loading dose in critically ill patients PMID: 34345128. Indian pediatric guidelines emphasize prompt empirical treatment without waiting for confirmatory tests PMID: 28361787.

Alternative: Azithromycin (macrolide; NCIT: C1005) is a suitable alternative PMID: 34345128; fluoroquinolones have been used adjunctively in some reports PMID: 28491211.

Supportive/interventional care: organ support in severe disease; vasodilators (iloprost) and anticoagulation for peripheral gangrene; renal replacement therapy for acute tubular necrosis PMID: 29169658; PMID: 28292166. "Early appropriate treatment and organ support can decrease the duration of illness and be life-saving" PMID: 34345128.

Not applicable: gene therapy, cell therapy, RNA-based therapy, targeted/immuno-oncology therapy, and pharmacogenomics are not part of standard management (surgery limited to debridement/amputation of necrotic tissue). No ITT-specific clinical-trial experimental agents (NCT IDs) were identified.

Treatment outcomes / adverse events: Response is rapid and near-universal with timely doxycycline PMID: 30150470. Doxycycline is generally well tolerated; historic concerns about pediatric dental staining are outweighed by benefit and short courses are considered safe per Indian pediatric guidance PMID: 28361787.

Section 13 — Prevention

No licensed human vaccine exists. Prevention is based on personal protective measures against tick bites and tick control on dogs and in the environment PMID: 15109588.

  • Primary prevention (behavioral/public health): tick repellents, permethrin-treated clothing, protective clothing (e.g., rolling up long sleeves), and frequent tick checks PMID: 33549976; PMID: 12653142. Reducing tick burden — "finding >10 ticks on the body" was the primary risk factor — is central PMID: 12653142.
  • One Health / veterinary control: controlling R. sanguineus on dogs and in the peridomestic environment reduces the reservoir/vector burden PMID: 40871278.
  • Chemoprophylaxis: doxycycline use was protective against seropositivity in an exposed cohort PMID: 12653142, though routine prophylaxis is not standard.
  • Secondary prevention: clinician awareness and early empirical doxycycline prevent progression to severe disease PMID: 42390463; PMID: 28361787.
  • Not applicable: immunization, genetic/carrier screening, and genetic counseling.

Notably, "most infected travellers cannot recall a preceding tick bite," underscoring the limits of avoidance alone and the importance of clinical vigilance PMID: 15109588.

Section 14 — Other Species / Natural Disease

Taxonomy of affected/involved species: Humans (Homo sapiens) are incidental hosts. The vector/reservoir is the brown dog tick Rhipicephalus sanguineus; ITTR has also been detected in Rhipicephalus turanicus PMID: 41650674. Dogs (Canis lupus familiaris) are key reservoir/amplifying hosts within a One Health transmission ecology PMID: 40871278.

Zoonosis / cross-species susceptibility: ITT/MSF is a tick-borne zoonosis PMID: 32997473. SFG rickettsiae infect multiple mammals: in a Colombian focus, incident SFG seroconversion reached 32.3% in equines vs 6.23% in humans, indicating shared cross-species exposure PMID: 30379820. Ticks serve as both vector and reservoir via transovarial/transstadial maintenance PMID: 40871278.

Comparative biology: Because the disease depends on conserved rickettsial invasion machinery (Sca2, RickA) and host actin/Arp2/3 pathways present across mammals, mechanisms are broadly conserved across host species PMID: 22612237; PMID: 22188208. (No VBO breed-specific susceptibility or OMIA natural-disease entry is established for ITT specifically.)

Section 15 — Model Organisms

Primary in vivo model — C3H/HeN mouse. IV inoculation of R. conorii (Malish 7) establishes disseminated endothelial infection by day 1; a high dose causes death on days 5–6 with vascular-injury-based meningoencephalitis and interstitial pneumonia, while a low dose recovers by day 10 with lymphohistiocytic perivasculitis, and Kupffer cell/hepatocyte infection forms transient hepatic granulomas. It is described as "the best available model for rickettsial disease with endothelial infection and injury" PMID: 7511715.

Phenotype recapitulation: The model reproduces the key human features — endothelial-target vasculitis, meningoencephalitis, interstitial pneumonia, hepatic involvement, and dose-dependent severity — making it well-suited to studying pathogenesis and immunity PMID: 7511715.

Immunological/mechanistic applications: The murine model established that CD8 T lymphocytes are required to clear rickettsiae from endothelium; CD8 depletion causes lethal/persistent infection, and adoptive transfer of immune CD4 or CD8 cells is protective PMID: 9164951.

In vitro models: Human endothelial cell invasion assays (defining Sca2 mammalian-association and actin-nucleation domains) PMID: 22612237 and RNAi screens in mammalian cells (SFG R. parkeri) mapping the Arp2/3–WAVE–Rho invasion pathway PMID: 22188208.

Limitations: Most experimental data use the Malish (MSF) strain rather than the indica subspecies specifically; murine dosing/route (IV) differs from natural tick inoculation; and models may not fully capture human age-dependent "malignant" severity.

Mechanistic Model / Interpretation

 Infected Rhipicephalus tick bite
      │ inoculates R. conorii subsp. indica into dermis
      ▼
     Local infection (eschar / tache noire)
      │ Sca2 + OmpA/OmpB adhesion
      ▼
   Adhesion & invasion of VASCULAR ENDOTHELIUM
      │ host Arp2/3 + WAVE2 + Rac GTPases nucleate actin
      ▼
   Cytosolic replication + actin-based motility (Sca2, RickA)
      │ cell-to-cell spread → dissemination
      ▼
   ENDOTHELIAL INFLAMMATION & INJURY (VASCULITIS)
├── TXA2-dependent platelet activation + thrombin → microthrombi
├── ↑ endothelin-1, ↑ permeability → edema / rash / MOF
└── endothelial membrane damage → antiphospholipid Abs (inferred)
      ▼
  Systemic small-vessel disease: skin, brain, lung, liver, kidney, eye, marrow
      │
   Host defense: CD8 T cells clear endothelial rickettsiae ──► recovery
   (failure / delay / age >65 ──► severe "malignant" form ──► death)
      ▲
   Doxycycline (halts replication) short-circuits the chain → rapid recovery

The model is internally consistent: a single upstream lesion — endothelial infection — explains the entire downstream phenotype (rash, coagulopathy, multi-organ vasculitis), the therapeutic target (intracellular bacterium → intracellular-active doxycycline), the immune requirement (CD8 clearance of infected endothelium), and prevention (block the tick bite that initiates the chain).

Evidence Base

PMID Study type Contribution
22628514 Genome sequence Identifies R. conorii subsp. indica strain ITTR as the ITT agent
15766388 MLST taxonomy Defines four R. conorii subspecies; ITTR genotype
41650674 Case report ITTR in human + tick; core clinical/lab phenotype
34345128 Review Endothelial vasculitis mechanism; doxycycline therapy
8584998 Human study TXA2-dependent platelet/coagulation activation in vivo
8679900 Case study Antiphospholipid antibodies from endothelial damage (inferred role)
15120155 Animal/tissue Oxidative-stress enzyme modulation; endothelial localization
22612237 In vitro Sca2 mediates adhesion, invasion, actin motility
22188208 RNAi screen Arp2/3–WAVE–Rho invasion pathway
7511715 Mouse model C3H/HeN endothelial-target rickettsiosis model
9164951 Mouse model CD8 T cells required for endothelial clearance
16481486 Genomics Reductive genome; host-ATP dependence; RickA
19379498 Genomics Virulence linked to genome reduction
12832625 Genomics Orphan genes reflect ongoing genome decay
32997473 Cohort (n=549) Incidence 9.44/100,000; age-dependent malignant forms
30972588 Cohort Severe MSF 26.4% vs 10.5% in elderly (p=0.002)
30150470 Prospective cohort Single-day doxycycline; defervescence 2.55±1.14 d
41795239 Pediatric cohort Fever/rash 100%, eschar 6%, thrombocytopenia 56%
42390463 Review Diagnostic modalities; PCR advantage; doxycycline
40608626 Case series Palm/sole rash, eschar; gltA/ompA confirmation
12653142 Epidemiology >10 ticks = risk; doxycycline/sleeves protective
15109588 Review Prevention via personal protection
40871278 One Health surveillance Dogs/companion animals in transmission ecology
30379820 Epidemiology Cross-species (equine 32.3%) SFG exposure
30451192 Case report Ocular retinitis; ITT within India's SFG
28361787 Guidelines IAP pediatric rickettsial guidance; doxycycline
40693676 Case report HLH complication (H-score 224)
20797742 Case report Infant meningoencephalitis with sequelae
35263931 Case report Meningoencephalitis MRI findings
29169658 Case series Symmetric peripheral gangrene / amputation
28491211 Case report Cerebral infarction
28292166 Case report Fatal late-diagnosed multivisceral failure
32998655 Case series Purpura fulminans; 18.2% mortality
29331008 Case report Atypical late (day 8) rash
33549976 Review Tick-bite personal protection measures
30522428 Case report PCR-positive, serology-negative acute phase; seroconversion
42658412 Case report Diagnostic challenges; differentials (measles, dengue)

Consistency: No contradictory findings emerged. Case reports, cohorts, guidelines, genomics, and experimental models all converge on a single coherent picture: an endothelium-tropic intracellular bacterium causing doxycycline-responsive systemic vasculitis.

Limitations and Knowledge Gaps

  1. Subspecies-specific data are sparse. Most mechanistic (Sca2, Arp2/3, CD8) and clinical-cohort evidence derives from the Malish/MSF strain or the broader R. conorii/SFG group, not the indica subspecies specifically. Subspecies are >98% identical and clinically indistinguishable, so extrapolation is reasonable but not formally validated for indica.
  2. No ITT-specific epidemiology. Incidence/prevalence figures (e.g., 9.44/100,000) come from Mediterranean/MSF cohorts; India-specific ITT burden is under-characterized and likely underreported PMID: 30451192.
  3. No host genomic/omics disease signatures (transcriptomics, proteomics, metabolomics, epigenomics) specific to ITT beyond antioxidant-enzyme modulation.
  4. Mechanism of severity is incomplete. Why some patients (especially elderly) develop "malignant" disease is not molecularly defined; the role of antiphospholipid antibodies in microthrombosis remains inferred, not proven PMID: 8679900.
  5. No human vaccine or genetic/pharmacogenomic component, so several template sections are intrinsically not applicable.
  6. Diagnostic timing gap: IFA is retrospective and PCR access is limited in endemic settings, leading to diagnostic delay and preventable severe outcomes PMID: 42390463; PMID: 28292166.

Proposed Follow-up Experiments / Actions

  1. Subspecies-specific characterization: Confirm Sca2/OmpA-mediated invasion kinetics and virulence of R. conorii subsp. indica (ITTR) in human endothelial cells and the C3H/HeN mouse, benchmarked against Malish, to validate mechanistic extrapolations.
  2. India-focused surveillance: Establish PCR-based (gltA/ompA) surveillance in Indian febrile-illness cohorts to quantify true ITT incidence, seasonal/geographic distribution, and severe-disease frequency.
  3. Host response omics: Perform transcriptomic/proteomic profiling of endothelial and PBMC responses in acute ITT to identify prognostic biomarkers distinguishing benign from malignant courses.
  4. Severity determinants: Test whether antiphospholipid-antibody titers, endothelin-1, and coagulation markers (prothrombin F1+2) predict progression to multi-organ failure — moving Branch A/C from inferred to demonstrated.
  5. Point-of-care diagnostics: Develop and validate a rapid acute-phase molecular or antigen test to close the IFA seroconversion gap and enable earlier doxycycline in endemic, resource-limited settings.
  6. One Health vector control trials: Evaluate whether canine R. sanguineus control (acaricides, environmental management) measurably reduces human ITT incidence in endemic foci.

Report compiled from 12 confirmed findings and 47 reviewed papers across 5 investigation iterations. Evidence types span human clinical (case reports, case series, cohorts, guidelines), model organism (C3H/HeN mouse), in vitro (endothelial invasion, RNAi screens), and computational/comparative genomics.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.3.0rc3.

Outcome Count
References checked 37
Resolved 37
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 3
Quoted claims found in source 3
Quoted claims not found in source 0
References weighed for topical relevance 37
On topic 22
Off topic 1

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

  • PMID:12832625 (4 mentions) - Birth and death of orphan genes in Rickettsia.
  • shared terms: conorii

Weighed against this report's own most characteristic terms: disease, tick, conorii, human, severe, acute, host, sfg, fever, indica, msf, doxycycline, itt, rash, endothelial, cell, cohort, clinical, meningoencephalitis, sca2.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 31
Resolved 31
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 0
Terms whose name was checked 9
Terms named correctly 1
Terms named as a different term 8

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • MONDO:0000229 (2 mentions) - the report calls it "MONDO"; MONDO calls it Indian tick typhus
  • HP:0200041 (1 mention) - the report calls it "cutaneous ulcer/eschar"; HP calls it Skin erosion
  • UBERON:0002097 (1 mention) - the report calls it "Rash, eschar/tache noire"; UBERON calls it skin of body*
  • UBERON:0000955 (1 mention) - the report calls it "Meningoencephalitis, cerebral infarction"; UBERON calls it brain
  • UBERON:0002048 (1 mention) - the report calls it "Interstitial pneumonia/infiltrates"; UBERON calls it lung
  • UBERON:0002107 (1 mention) - the report calls it "Transaminitis, hepatic granulomas (Kupffer cell/hepatocyte infection)"; UBERON calls it liver
  • UBERON:0002113 (1 mention) - the report calls it "Proteinuria, acute tubular necrosis/renal failure"; UBERON calls it kidney
  • UBERON:0000178 (1 mention) - the report calls it "Thrombocytopenia, HLH"; UBERON calls it blood