🏷

Classifications

Harrison's Part

⚙

Pathophysiology

7

Rickettsia felis Ribosomal Translation

R. felis, like other bacteria, depends on 70S-ribosome translation of its mRNA. Doxycycline targets this conserved bacterial translation machinery, explaining why a tetracycline is the preferred treatment for flea-borne rickettsioses.

translation GO:0006412

Show evidence (1 reference)

PMID:24336183 SUPPORT REVIEW SYNTHESIS Other

"The ribosome is one of the main antibiotic targets in the bacterial cell."

The review establishes the conserved bacterial ribosome target represented by this R. felis translation node.

Obligate Intracellular Rickettsia felis Niche

R. felis is an obligately intracellular Gram-negative coccobacillus. Occupancy of a eukaryotic cytosolic niche makes the organism intrinsically difficult to treat with antimicrobials that do not penetrate host cells.

biological process involved in interaction with host GO:0051701

Show evidence (3 references)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Flea-borne rickettsiae are small (~1.3 X 0.4 µm) gram-negative coccobacilli."

The review characterizes flea-borne rickettsiae as Gram-negative coccobacilli.

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Thus, they have a strict obligately intracellular lifestyle and depend on the host cell’s cytosol to provide the nutrients to survive."

The review explains the obligate intracellular niche of flea-borne rickettsiae.

PMID:18611821 SUPPORT REVIEW SYNTHESIS Other

"The intracellular location of some microorganisms allow them to resist antibiotics with poor ability to penetrate eukaryotic cell membranes, such as the beta-lactam compounds."

The review supports the pharmacologic consequence of an intracellular bacterial niche.

Dermal Rickettsial Inoculation

After R. felis or another flea-borne rickettsia is inoculated into skin, mononuclear antigen-presenting cells can encounter the organism and carry the response toward lymphatics and regional lymph nodes.

biological process involved in interaction with host GO:0051701

Downstream

Endothelial Rickettsial Invasion and Vascular Leak Flea-borne rickettsiae can disseminate from skin and lymphatics to the bloodstream and then infect vascular endothelium.

Eschar Local inoculation occasionally produces an eschar in flea-borne spotted fever.

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"After the inoculation of rickettsiae into the skin, macrophages and dendritic cells target the organism, which then spread through the lymphatics to regional lymph nodes."

The review describes the early dermal step after cutaneous rickettsial inoculation.

Endothelial Rickettsial Invasion and Vascular Leak

Rickettsiae disseminate hematogenously into vascular endothelial cells. On endothelial surfaces, rickettsial OmpB can use ANXA2 for adherence, while pathogenic spotted-fever rickettsiae also use an FGFR1/HSPG entry program to internalize into microvascular endothelial cells. Systemic endothelial infection and inflammatory injury then increase vascular permeability.

vascular endothelial cell CL:0002139

biological process involved in interaction with host GO:0051701 positive regulation of vascular permeability GO:0043117 ↑ INCREASED

Downstream

Chemokine and VEGF Response Endothelial rickettsial infection is paired with systemic inflammatory and vascular-permeability mediators during acute R. felis infection.

Rickettsial NF-kappaB-Dependent Endothelial Survival Rickettsial invasion of endothelial cells activates an NF-kappaB-dependent anti-apoptotic program that lets infected cells survive during bacterial replication.

Maculopapular rash Vascular permeability and cutaneous microvascular inflammation contribute to the rickettsial rash.

Show evidence (3 references)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"The rickettsiae escape hematogenously and infect endothelial cells. Systemic endothelial infection and resultant inflammatory damage lead to increased vascular permeability."

The review links hematogenous endothelial infection to vascular leak in flea-borne rickettsioses.

PMID:31253864 SUPPORT Model Organism

"We found that deletion of ANXA2 impeded rickettsial attachment to the ECs in vitro and blocked rickettsial adherence to the blood vessel luminal surface in vivo."

The adhesion study supports ANXA2-dependent rickettsial attachment to endothelial cells.

PMID:28806774 SUPPORT In Vitro

"Inhibition of HSPGs by heparinase and FGFRs by AZD4547 (a selective small-molecule inhibitor) results in significant reduction in rickettsial internalization into cultured human microvascular endothelial cells (ECs), which represent the primary targets of pathogenic rickettsiae during human infections."

Cultured human endothelial-cell data support HSPG/FGFR-dependent internalization as a spotted-fever rickettsial entry mechanism.

Rickettsial NF-kappaB-Dependent Endothelial Survival

In R. rickettsii-infected cells, NF-kappaB activation masks an apoptosis signal in infected host cells and thereby preserves the intracellular endothelial niche long enough for rickettsial replication and cell-to-cell spread.

vascular endothelial cell CL:0002139

positive regulation of NF-kappaB transcription factor activity GO:0043123 ↑ INCREASED negative regulation of apoptotic process GO:0043066 ↑ INCREASED

Show evidence (1 reference)

PMID:9539792 SUPPORT INDIRECT In Vitro

"However, when R. rickettsii-induced activation of NF-kappa B was inhibited, apoptosis of infected but not uninfected endothelial cells rapidly ensued."

R. rickettsii infection of cultured cells shows the NF-kappaB-dependent host-cell survival switch expected to support an endothelial niche for spotted-fever rickettsiae.

NK and CD8 IFN-Gamma Rickettsial Control

Natural killer cells and CD8-positive T cells limit rickettsial infection severity through IFN-gamma-linked and cytotoxic responses; NK-cell loss in a Rickettsia mouse model impaired clearance, lowered IFN-gamma, and worsened infection-induced hepatic thrombosis.

natural killer cell CL:0000623 CD8-positive, alpha-beta T cell CL:0000625

response to type II interferon GO:0034341 ↑ INCREASED natural killer cell mediated cytotoxicity GO:0042267 ↑ INCREASED

Show evidence (1 reference)

PMID:22617213 SUPPORT INDIRECT Model Organism

"NK cell-deficient Rag(-/-)γc(-/-) animals displayed significantly increased susceptibility to Rickettsia infection compared with NK cell-sufficient Rag(-/-) mice"

The endothelial rickettsiosis mouse model supports NK-cell/IFN-gamma control as a protective arm of host defense against rickettsiae.

Chemokine and VEGF Response

Acute R. felis mono-infection in febrile children is associated with higher circulating IL-8, IP-10, MCP-1, MIP-1-alpha, and VEGF, linking infection to leukocyte-recruiting chemokines and a vascular permeability mediator.

cytokine production GO:0001816 ↑ INCREASED positive regulation of vascular permeability GO:0043117 ↑ INCREASED

Downstream

Fever The systemic inflammatory response contributes to fever.

Headache Systemic inflammatory illness contributes to headache.

Neurological manifestations Systemic rickettsial endothelial inflammation can include neurologic signs in a minority of reported flea-borne spotted fever cases.

Show evidence (1 reference)

PMID:29736763 SUPPORT Human Clinical

"Levels of IL-8 (interleukin-8), IP-10 (interferon-γ-induced protein-10), MCP-1 (monocyte chemotactic protein-1), MIP-1α (macrophage inflammatory protein-1α) and VEGF (vascular endothelial growth factor) were significantly elevated in R. felis mono-infection"

Serum from acutely ill children with R. felis mono-infection showed higher chemokine and VEGF concentrations.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

5

Immune 1

Maculopapular rash FREQUENT Maculopapular exanthema HP:0040186

Show evidence (2 references)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Human Clinical

"Signs and symptoms from these compiled cases include fever (94%), rash (71%), neurologic signs (15%), gastrointestinal symptoms (9%), and cough (9%)."

The review supports rash as frequent in compiled FBSF cases.

PMID:33574726 SUPPORT REVIEW SYNTHESIS Human Clinical

"The rash is usually maculopapular, and unlike murine typhus, eschar has been noted in 12% of cases."

The review states that the FBSF rash is usually maculopapular.

Integument 1

Eschar OCCASIONAL HP:6000793

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Human Clinical

"The rash is usually maculopapular, and unlike murine typhus, eschar has been noted in 12% of cases."

The review reports eschar in a minority of FBSF cases.

Metabolism 1

Fever VERY_FREQUENT HP:0001945

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Human Clinical

"Signs and symptoms from these compiled cases include fever (94%), rash (71%), neurologic signs (15%), gastrointestinal symptoms (9%), and cough (9%)."

The review summarizes fever frequency from compiled FBSF cases.

Nervous System 2

Headache HP:0002315

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Headache, malaise, and myalgia are frequent symptoms that accompany fever."

The review identifies headache as a frequent flea-borne rickettsiosis symptom.

Neurological manifestations OCCASIONAL Abnormality of the nervous system HP:0000707

Coarse binding: source unspecified

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Human Clinical

"Signs and symptoms from these compiled cases include fever (94%), rash (71%), neurologic signs (15%), gastrointestinal symptoms (9%), and cough (9%)."

The review's compiled FBSF cases quantify neurologic signs as an occasional finding but do not specify their form.

💊

Medical Actions

1

Doxycycline

Action: Pharmacotherapy NCIT:C15986

Agent: doxycycline CHEBI:50845

Platform: Small molecule

Preferred empiric tetracycline therapy for flea-borne rickettsioses; because early serology is often negative, treatment is started when the syndrome is suspected rather than waiting for retrospective seroconversion.

Mechanism Target:

Rickettsia felis Ribosomal Translation — Doxycycline inhibits bacterial ribosomal protein synthesis.

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Doxycycline is the preferred agent for the treatment of flea-borne rickettsioses."

The review identifies doxycycline as the preferred treatment.

🔬

Diagnosis

2

Paired-serum indirect immunofluorescence assay

Serologic confirmation of a rickettsial illness is retrospective, using paired acute and convalescent sera to show seroconversion or a fourfold antibody-titer rise; antibodies to R. felis cross-react more strongly with spotted-fever-group antigen than with typhus-group antigen.

indirect immunofluorescence assay NCIT:C25294

Results: Seroconversion or a fourfold rise in spotted-fever-group antibody titer supports infection.

Show evidence (2 references)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"The serologic confirmation of diagnosis is therefore retrospective – requiring demonstration of seroconversion or 4-fold increase in antibody titer from acute- and convalescent-phase specimens."

The review describes the paired-serum criterion used to confirm a rickettsial illness.

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Antibodies against R. felis have been shown to be more cross reactive to spotted fever group antigen than to typhus group antigen."

The review supports use of spotted-fever-group serology for R. felis infection.

Skin-biopsy Rickettsia qPCR

Real-time PCR on skin-biopsy material can support an acute spotted-fever or typhus-group rickettsiosis diagnosis while first-serum serology is still negative; skin-biopsy qPCR is substantially more often positive than whole-blood qPCR because circulating organisms are few.

polymerase chain reaction NCIT:C17003

Results: A positive pan-rickettsial or group-specific qPCR supports acute rickettsial infection.

Show evidence (1 reference)

PMID:25706392 SUPPORT INDIRECT Human Clinical

"Among 44 skin biopsies obtained from patients with confirmed diagnosis, the first duplex was positive in 24 samples (54.5%), with three patients positive by Rtt qPCR."

The Tunisian rickettsiosis series shows that direct molecular testing of skin material can detect Rickettsia DNA in acute human rickettsioses.

📊

Prevalence

1

Febrile patients in rural Senegal

Period Prevalence >1 in 1,000

PCR positivity was 15% among febrile patients in rural Senegal in a cross-region study of France, North Africa, and sub-Saharan Africa; this is a focal febrile-patient fraction rather than a population incidence rate.

Show evidence (1 reference)

PMID:24188709 SUPPORT Human Clinical

"The risks were lowest in France, Tunisia, and Algeria (1%), and highest in rural Senegal (15%)."

Supports the focal high R. felis PCR-positivity fraction among febrile patients.

🦠

Infectious Agent

1

Rickettsia felis

Obligate intracellular flea-associated Rickettsia species implicated as the cause of flea-borne spotted fever.

Rickettsia felis NCBITaxon:42862

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Murine typhus and flea-borne spotted fever are undifferentiated febrile illnesses caused by Rickettsia typhi and Rickettsia felis, respectively."

The review names R. felis as the etiologic organism of flea-borne spotted fever.

↔️

Transmission

1

Cat-flea-associated transmission

R. felis is primarily associated with the ubiquitous cat flea Ctenocephalides felis, although the organism has been molecularly detected in many arthropods and vertebrates and its definitive vertebrate reservoir is not established.

Show evidence (1 reference)

PMID:33574726 SUPPORT REVIEW SYNTHESIS Other

"Since the discovery of R. felis infecting a cat flea colony in California in 1990,77 it has been increasingly found within a diverse variety of vertebrate and invertebrate species throughout the world.3 Its primary recognized invertebrate host and reservoir is C. felis."

Supports C. felis as the principal recognized invertebrate host and reservoir for R. felis.

{ }

Source YAML

click to show

name: Flea-Borne Spotted Fever
creation_date: "2026-09-28T13:09:20Z"
category: Infectious Disease
description: >-
  Flea-borne spotted fever is a febrile rickettsiosis attributed to the
  obligately intracellular Gram-negative bacterium Rickettsia felis. R. felis is
  carried by cat fleas, and reported human disease presents as an
  undifferentiated fever that can include headache, myalgia, maculopapular rash,
  and occasional eschar. The causal role of R. felis in every PCR-positive
  febrile illness is less settled than the R. typhi-murine typhus relationship,
  because R. felis DNA has also been detected in afebrile controls and on skin
  swabs; curated mechanisms therefore focus on rickettsial processes directly
  supported for R. felis or shared across flea-borne rickettsiae.
disease_term:
  preferred_term: flea-borne spotted fever
  term:
    id: MONDO:0019364
    label: pseudotyphus of California
parents:
- Spotted fever rickettsiosis
synonyms:
- Pseudotyphus of California
- Rickettsia felis infection

references:
- reference: PMID:33574726
  title: "Manifestations and Management of Flea-Borne Rickettsioses."
  findings:
  - statement: >-
      Review defining murine typhus and flea-borne spotted fever as flea-borne
      infections caused by Rickettsia typhi and Rickettsia felis, respectively,
      and summarizing R. felis uncertainty, symptoms, serology, and doxycycline
      treatment.
    supporting_text: >-
      Murine typhus and flea-borne spotted fever are undifferentiated febrile
      illnesses caused by Rickettsia typhi and Rickettsia felis, respectively.
- reference: PMID:31253864
  title: >-
    A new role for host annexin A2 in establishing bacterial adhesion to
    vascular endothelial cells: lines of evidence from atomic force microscopy
    and an in vivo study.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      Endothelial ANXA2 functions as a luminal-surface rickettsial adherence
      receptor, with OmpB as the bacterial ligand.
    supporting_text: >-
      We found that deletion of ANXA2 impeded rickettsial attachment to the ECs
      in vitro and blocked rickettsial adherence to the blood vessel luminal
      surface in vivo.
- reference: PMID:28806774
  title: >-
    Fibroblast growth factor receptor-1 mediates internalization of pathogenic
    spotted fever rickettsiae into host endothelium.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      FGFR1/heparan-sulfate signaling contributes to pathogenic spotted-fever
      rickettsial internalization into human microvascular endothelial cells.
    supporting_text: >-
      Inhibition of HSPGs by heparinase and FGFRs by AZD4547 (a selective
      small-molecule inhibitor) results in significant reduction in rickettsial
      internalization into cultured human microvascular endothelial cells (ECs),
      which represent the primary targets of pathogenic rickettsiae during human
      infections.
- reference: PMID:29736763
  title: "Serum cytokine responses in Rickettsia felis infected febrile children, Ghana."
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      Human R. felis mono-infection is associated with increased serum IL-8,
      IP-10, MCP-1, MIP-1-alpha, and VEGF in febrile Ghanaian children.
    supporting_text: >-
      Levels of IL-8 (interleukin-8), IP-10 (interferon-γ-induced protein-10),
      MCP-1 (monocyte chemotactic protein-1), MIP-1α (macrophage inflammatory
      protein-1α) and VEGF (vascular endothelial growth factor) were
      significantly elevated in R. felis mono-infection
- reference: PMID:12860594
  title: Pathogenic mechanisms of diseases caused by Rickettsia.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      Review supporting the shared typhus/spotted-fever sequence from dermal
      rickettsial entry to endothelial dissemination, permeability, edema, and
      cytotoxic/NK-cell immunity.
    supporting_text: >-
      The pathogenetic sequence includes rickettsial entry into the dermis,
      hematogenous dissemination to vascular endothelial cells
- reference: PMID:9539792
  title: >-
    NF-kappa B-dependent inhibition of apoptosis is essential for host
    cellsurvival during Rickettsia rickettsii infection.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      Rickettsia rickettsii activates endothelial NF-kappaB to suppress
      host-cell apoptosis during intracellular infection.
    supporting_text: >-
      R. rickettsii, therefore, appeared to inhibit host cell apoptosis via a
      mechanism dependent on NF-kappa B activation.
- reference: PMID:22617213
  title: >-
    Contribution of NK cells to the innate phase of host protection against an
    intracellular bacterium targeting systemic endothelium.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      NK-cell IFN-gamma and cytotoxicity protect mice against endothelial
      rickettsial infection and infection-induced thrombosis.
    supporting_text: >-
      Together, these findings reveal that NK cells mediate the innate phase of
      host protection against infection with rickettsiae, most likely via IFN-γ
      production.
- reference: PMID:24188709
  title: Common epidemiology of Rickettsia felis infection and malaria, Africa.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      R. felis PCR positivity among febrile patients varied geographically and
      reached 15% in rural Senegal in a 3,122-patient comparison of France,
      North Africa, and sub-Saharan Africa.
    supporting_text: >-
      The risks were lowest in France, Tunisia, and Algeria (1%), and highest
      in rural Senegal (15%).
- reference: PMID:25706392
  title: >-
    Comparison of two quantitative real time PCR assays for Rickettsia
    detection in patients from Tunisia.
  found_in:
  - Flea_Borne_Spotted_Fever-deep-research-openscientist.md
  findings:
  - statement: >-
      Rickettsial duplex qPCR was markedly more often positive from skin
      biopsies than from whole blood in confirmed Tunisian rickettsiosis.
    supporting_text: >-
      Among 44 skin biopsies obtained from patients with confirmed diagnosis,
      the first duplex was positive in 24 samples (54.5%), with three patients
      positive by Rtt qPCR.
- reference: PMID:24336183
  title: Ribosome-targeting antibiotics and mechanisms of bacterial resistance.
  findings:
  - statement: Review establishing the bacterial ribosome as a major antibiotic target.
    supporting_text: The ribosome is one of the main antibiotic targets in the bacterial cell.
- reference: PMID:18611821
  title: Intracellular organisms.
  findings:
  - statement: >-
      Review supporting intracellular bacterial niches as a reason that
      poorly cell-penetrant agents can be ineffective.
    supporting_text: >-
      The intracellular location of some microorganisms allow them to resist
      antibiotics with poor ability to penetrate eukaryotic cell membranes, such
      as the beta-lactam compounds.

classifications:
  harrisons_chapter:
  - classification_value: INFECTIOUS_DISEASES
    evidence:
    - reference: PMID:33574726
      reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Murine typhus and flea-borne spotted fever are undifferentiated febrile
        illnesses caused by Rickettsia typhi and Rickettsia felis, respectively.
        These organisms are small gram-negative obligately intracellular
        coccobacilli transmitted to humans by fleas.
      explanation: >-
        Defines flea-borne spotted fever as a bacterial rickettsial infection
        transmitted by fleas, placing it in Harrison's Infectious Diseases Part.

infectious_agent:
- name: Rickettsia felis
  infectious_agent_term:
    preferred_term: Rickettsia felis
    term:
      id: NCBITaxon:42862
      label: Rickettsia felis
  description: >-
    Obligate intracellular flea-associated Rickettsia species implicated as the
    cause of flea-borne spotted fever.
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Murine typhus and flea-borne spotted fever are undifferentiated febrile
      illnesses caused by Rickettsia typhi and Rickettsia felis, respectively.
    explanation: The review names R. felis as the etiologic organism of flea-borne spotted fever.

transmission:
- name: Cat-flea-associated transmission
  description: >-
    R. felis is primarily associated with the ubiquitous cat flea
    Ctenocephalides felis, although the organism has been molecularly detected
    in many arthropods and vertebrates and its definitive vertebrate reservoir
    is not established.
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Since the discovery of R. felis infecting a cat flea colony in California
      in 1990,77 it has been increasingly found within a diverse variety of
      vertebrate and invertebrate species throughout the world.3 Its primary
      recognized invertebrate host and reservoir is C. felis.
    explanation: >-
      Supports C. felis as the principal recognized invertebrate host and
      reservoir for R. felis.

prevalence:
- population: Febrile patients in rural Senegal
  measure_type: PERIOD_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  notes: >-
    PCR positivity was 15% among febrile patients in rural Senegal in a
    cross-region study of France, North Africa, and sub-Saharan Africa; this is
    a focal febrile-patient fraction rather than a population incidence rate.
  evidence:
  - reference: PMID:24188709
    reference_title: Common epidemiology of Rickettsia felis infection and malaria, Africa.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The risks were lowest in France, Tunisia, and Algeria (1%), and highest
      in rural Senegal (15%).
    explanation: >-
      Supports the focal high R. felis PCR-positivity fraction among febrile
      patients.

pathophysiology:
- name: Rickettsia felis Ribosomal Translation
  description: >-
    R. felis, like other bacteria, depends on 70S-ribosome translation of its
    mRNA. Doxycycline targets this conserved bacterial translation machinery,
    explaining why a tetracycline is the preferred treatment for flea-borne
    rickettsioses.
  role: therapeutic_vulnerability
  conforms_to: "bacterial_protein_synthesis_inhibition#Bacterial mRNA Translation by the Ribosome"
  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: >-
      The review establishes the conserved bacterial ribosome target represented
      by this R. felis translation node.
- name: Obligate Intracellular Rickettsia felis Niche
  description: >-
    R. felis is an obligately intracellular Gram-negative coccobacillus.
    Occupancy of a eukaryotic cytosolic niche makes the organism intrinsically
    difficult to treat with antimicrobials that do not penetrate host cells.
  role: intrinsic_resistance
  conforms_to: "intracellular_pathogen_persistence#Intracellular Niche and Beta-Lactam Exclusion"
  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:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Flea-borne rickettsiae are small (~1.3 X 0.4 µm) gram-negative
      coccobacilli.
    explanation: The review characterizes flea-borne rickettsiae as Gram-negative coccobacilli.
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Thus, they have a strict obligately intracellular lifestyle and depend on
      the host cell’s cytosol to provide the nutrients to survive.
    explanation: The review explains the obligate intracellular niche of flea-borne rickettsiae.
  - reference: PMID:18611821
    reference_title: Intracellular organisms.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The intracellular location of some microorganisms allow them to resist
      antibiotics with poor ability to penetrate eukaryotic cell membranes, such
      as the beta-lactam compounds.
    explanation: >-
      The review supports the pharmacologic consequence of an intracellular
      bacterial niche.
- name: Dermal Rickettsial Inoculation
  description: >-
    After R. felis or another flea-borne rickettsia is inoculated into skin,
    mononuclear antigen-presenting cells can encounter the organism and carry the
    response toward lymphatics and regional lymph nodes.
  role: entry_process
  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:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      After the inoculation of rickettsiae into the skin, macrophages and
      dendritic cells target the organism, which then spread through the
      lymphatics to regional lymph nodes.
    explanation: >-
      The review describes the early dermal step after cutaneous rickettsial
      inoculation.
  downstream:
  - target: Endothelial Rickettsial Invasion and Vascular Leak
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Flea-borne rickettsiae can disseminate from skin and lymphatics to the
      bloodstream and then infect vascular endothelium.
  - target: Eschar
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Local inoculation occasionally produces an eschar in flea-borne spotted fever.
- name: Endothelial Rickettsial Invasion and Vascular Leak
  description: >-
    Rickettsiae disseminate hematogenously into vascular endothelial cells. On
    endothelial surfaces, rickettsial OmpB can use ANXA2 for adherence, while
    pathogenic spotted-fever rickettsiae also use an FGFR1/HSPG entry program
    to internalize into microvascular endothelial cells. Systemic endothelial
    infection and inflammatory injury then increase vascular permeability.
  role: effector
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: vascular endothelial cell
    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
  - preferred_term: positive regulation of vascular permeability
    modifier: INCREASED
    term:
      id: GO:0043117
      label: positive regulation of vascular permeability
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The rickettsiae escape hematogenously and infect endothelial cells.
      Systemic endothelial infection and resultant inflammatory damage lead to
      increased vascular permeability.
    explanation: >-
      The review links hematogenous endothelial infection to vascular leak in
      flea-borne rickettsioses.
  - reference: PMID:31253864
    reference_title: >-
      A new role for host annexin A2 in establishing bacterial adhesion to
      vascular endothelial cells: lines of evidence from atomic force microscopy
      and an in vivo study.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We found that deletion of ANXA2 impeded rickettsial attachment to the ECs
      in vitro and blocked rickettsial adherence to the blood vessel luminal
      surface in vivo.
    explanation: >-
      The adhesion study supports ANXA2-dependent rickettsial attachment to
      endothelial cells.
  - reference: PMID:28806774
    reference_title: >-
      Fibroblast growth factor receptor-1 mediates internalization of pathogenic
      spotted fever rickettsiae into host endothelium.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Inhibition of HSPGs by heparinase and FGFRs by AZD4547 (a selective
      small-molecule inhibitor) results in significant reduction in rickettsial
      internalization into cultured human microvascular endothelial cells (ECs),
      which represent the primary targets of pathogenic rickettsiae during human
      infections.
    explanation: >-
      Cultured human endothelial-cell data support HSPG/FGFR-dependent
      internalization as a spotted-fever rickettsial entry mechanism.
  downstream:
  - target: Chemokine and VEGF Response
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Endothelial rickettsial infection is paired with systemic inflammatory and
      vascular-permeability mediators during acute R. felis infection.
  - target: Rickettsial NF-kappaB-Dependent Endothelial Survival
    causal_link_type: DIRECT
    description: >-
      Rickettsial invasion of endothelial cells activates an NF-kappaB-dependent
      anti-apoptotic program that lets infected cells survive during bacterial
      replication.
  - target: Maculopapular rash
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Vascular permeability and cutaneous microvascular inflammation contribute
      to the rickettsial rash.
- name: Rickettsial NF-kappaB-Dependent Endothelial Survival
  description: >-
    In R. rickettsii-infected cells, NF-kappaB activation masks an apoptosis
    signal in infected host cells and thereby preserves the intracellular
    endothelial niche long enough for rickettsial replication and cell-to-cell
    spread.
  role: effector
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: vascular endothelial cell
    term:
      id: CL:0002139
      label: endothelial cell of vascular tree
  biological_processes:
  - preferred_term: positive regulation of NF-kappaB transcription factor activity
    modifier: INCREASED
    term:
      id: GO:0043123
      label: positive regulation of canonical NF-kappaB signal transduction
  - preferred_term: negative regulation of apoptotic process
    modifier: INCREASED
    term:
      id: GO:0043066
      label: negative regulation of apoptotic process
  evidence:
  - reference: PMID:9539792
    reference_title: >-
      NF-kappa B-dependent inhibition of apoptosis is essential for host
      cellsurvival during Rickettsia rickettsii infection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: INDIRECT
    snippet: >-
      However, when R. rickettsii-induced activation of NF-kappa B was
      inhibited, apoptosis of infected but not uninfected endothelial cells
      rapidly ensued.
    explanation: >-
      R. rickettsii infection of cultured cells shows the NF-kappaB-dependent
      host-cell survival switch expected to support an endothelial niche for
      spotted-fever rickettsiae.
- name: NK and CD8 IFN-Gamma Rickettsial Control
  description: >-
    Natural killer cells and CD8-positive T cells limit rickettsial infection
    severity through IFN-gamma-linked and cytotoxic responses; NK-cell loss in a
    Rickettsia mouse model impaired clearance, lowered IFN-gamma, and worsened
    infection-induced hepatic thrombosis.
  role: protective
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: natural killer cell
    term:
      id: CL:0000623
      label: natural killer cell
  - preferred_term: CD8-positive, alpha-beta T cell
    term:
      id: CL:0000625
      label: CD8-positive, alpha-beta T cell
  biological_processes:
  - preferred_term: response to type II interferon
    modifier: INCREASED
    term:
      id: GO:0034341
      label: response to type II interferon
  - preferred_term: natural killer cell mediated cytotoxicity
    modifier: INCREASED
    term:
      id: GO:0042267
      label: natural killer cell mediated cytotoxicity
  evidence:
  - reference: PMID:22617213
    reference_title: >-
      Contribution of NK cells to the innate phase of host protection against an
      intracellular bacterium targeting systemic endothelium.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: >-
      NK cell-deficient Rag(-/-)γc(-/-) animals displayed significantly
      increased susceptibility to Rickettsia infection compared with NK
      cell-sufficient Rag(-/-) mice
    explanation: >-
      The endothelial rickettsiosis mouse model supports NK-cell/IFN-gamma
      control as a protective arm of host defense against rickettsiae.
- name: Chemokine and VEGF Response
  description: >-
    Acute R. felis mono-infection in febrile children is associated with higher
    circulating IL-8, IP-10, MCP-1, MIP-1-alpha, and VEGF, linking infection to
    leukocyte-recruiting chemokines and a vascular permeability mediator.
  role: immune_response
  biological_scale: ORGANISM
  biological_processes:
  - preferred_term: cytokine production
    term:
      id: GO:0001816
      label: cytokine production
    modifier: INCREASED
  - preferred_term: positive regulation of vascular permeability
    term:
      id: GO:0043117
      label: positive regulation of vascular permeability
    modifier: INCREASED
  evidence:
  - reference: PMID:29736763
    reference_title: "Serum cytokine responses in Rickettsia felis infected febrile children, Ghana."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Levels of IL-8 (interleukin-8), IP-10 (interferon-γ-induced protein-10),
      MCP-1 (monocyte chemotactic protein-1), MIP-1α (macrophage inflammatory
      protein-1α) and VEGF (vascular endothelial growth factor) were
      significantly elevated in R. felis mono-infection
    explanation: >-
      Serum from acutely ill children with R. felis mono-infection showed higher
      chemokine and VEGF concentrations.
  downstream:
  - target: Fever
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: The systemic inflammatory response contributes to fever.
  - target: Headache
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Systemic inflammatory illness contributes to headache.
  - target: Neurological manifestations
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Systemic rickettsial endothelial inflammation can include neurologic
      signs in a minority of reported flea-borne spotted fever cases.

phenotypes:
- category: Clinical
  name: Fever
  description: Fever is the dominant reported symptom in flea-borne spotted fever.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Signs and symptoms from these compiled cases include fever (94%), rash
      (71%), neurologic signs (15%), gastrointestinal symptoms (9%), and cough
      (9%).
    explanation: The review summarizes fever frequency from compiled FBSF cases.
- category: Clinical
  name: Headache
  description: >-
    Headache is a frequent symptom accompanying the fever of flea-borne
    rickettsioses.
  phenotype_term:
    preferred_term: Headache
    term:
      id: HP:0002315
      label: Headache
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Headache, malaise, and myalgia are frequent symptoms that accompany fever.
    explanation: The review identifies headache as a frequent flea-borne rickettsiosis symptom.
- category: Clinical
  name: Maculopapular rash
  description: >-
    The rash reported in flea-borne spotted fever is usually maculopapular.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Maculopapular rash
    term:
      id: HP:0040186
      label: Maculopapular exanthema
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Signs and symptoms from these compiled cases include fever (94%), rash
      (71%), neurologic signs (15%), gastrointestinal symptoms (9%), and cough
      (9%).
    explanation: The review supports rash as frequent in compiled FBSF cases.
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: The rash is usually maculopapular, and unlike murine typhus, eschar has been noted in 12% of cases.
    explanation: The review states that the FBSF rash is usually maculopapular.
- category: Neurological
  name: Neurological manifestations
  description: >-
    A compiled flea-borne spotted fever case set reported unspecified
    neurologic signs in 15% of published cases.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Neurological manifestations
    term:
      id: HP:0000707
      label: Abnormality of the nervous system
    coarse_binding_basis: SOURCE_UNSPECIFIED
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Signs and symptoms from these compiled cases include fever (94%), rash
      (71%), neurologic signs (15%), gastrointestinal symptoms (9%), and cough
      (9%).
    explanation: >-
      The review's compiled FBSF cases quantify neurologic signs as an
      occasional finding but do not specify their form.
- category: Clinical
  name: Eschar
  description: >-
    An inoculation eschar is reported in a minority of flea-borne spotted fever
    cases.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Eschar
    term:
      id: HP:6000793
      label: Eschar
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: The rash is usually maculopapular, and unlike murine typhus, eschar has been noted in 12% of cases.
    explanation: The review reports eschar in a minority of FBSF cases.

diagnosis:
- name: Paired-serum indirect immunofluorescence assay
  description: >-
    Serologic confirmation of a rickettsial illness is retrospective, using
    paired acute and convalescent sera to show seroconversion or a fourfold
    antibody-titer rise; antibodies to R. felis cross-react more strongly with
    spotted-fever-group antigen than with typhus-group antigen.
  diagnosis_term:
    preferred_term: indirect immunofluorescence assay
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  results: Seroconversion or a fourfold rise in spotted-fever-group antibody titer supports infection.
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The serologic confirmation of diagnosis is therefore retrospective –
      requiring demonstration of seroconversion or 4-fold increase in antibody
      titer from acute- and convalescent-phase specimens.
    explanation: >-
      The review describes the paired-serum criterion used to confirm a
      rickettsial illness.
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Antibodies against R. felis have been shown to be more cross reactive to
      spotted fever group antigen than to typhus group antigen.
    explanation: The review supports use of spotted-fever-group serology for R. felis infection.
- name: Skin-biopsy Rickettsia qPCR
  description: >-
    Real-time PCR on skin-biopsy material can support an acute spotted-fever or
    typhus-group rickettsiosis diagnosis while first-serum serology is still
    negative; skin-biopsy qPCR is substantially more often positive than
    whole-blood qPCR because circulating organisms are few.
  diagnosis_term:
    preferred_term: polymerase chain reaction
    term:
      id: NCIT:C17003
      label: Polymerase Chain Reaction
  results: A positive pan-rickettsial or group-specific qPCR supports acute rickettsial infection.
  evidence:
  - reference: PMID:25706392
    reference_title: >-
      Comparison of two quantitative real time PCR assays for Rickettsia
      detection in patients from Tunisia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Among 44 skin biopsies obtained from patients with confirmed diagnosis,
      the first duplex was positive in 24 samples (54.5%), with three patients
      positive by Rtt qPCR.
    explanation: >-
      The Tunisian rickettsiosis series shows that direct molecular testing of
      skin material can detect Rickettsia DNA in acute human rickettsioses.

treatments:
- name: Doxycycline
  description: >-
    Preferred empiric tetracycline therapy for flea-borne rickettsioses; because
    early serology is often negative, treatment is started when the syndrome is
    suspected rather than waiting for retrospective seroconversion.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: doxycycline
      term:
        id: CHEBI:50845
        label: doxycycline
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Rickettsia felis Ribosomal Translation
    description: Doxycycline inhibits bacterial ribosomal protein synthesis.
  evidence:
  - reference: PMID:33574726
    reference_title: "Manifestations and Management of Flea-Borne Rickettsioses."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Doxycycline is the preferred agent for the treatment of flea-borne rickettsioses.
    explanation: The review identifies doxycycline as the preferred treatment.

📚

References & Deep Research

References

11

PMID:33574726

Manifestations and Management of Flea-Borne Rickettsioses.

1 finding

Review defining murine typhus and flea-borne spotted fever as flea-borne infections caused by Rickettsia typhi and Rickettsia felis, respectively, and summarizing R. felis uncertainty, symptoms, serology, and doxycycline treatment.

"Murine typhus and flea-borne spotted fever are undifferentiated febrile illnesses caused by Rickettsia typhi and Rickettsia felis, respectively."

PMID:31253864

A new role for host annexin A2 in establishing bacterial adhesion to vascular endothelial cells: lines of evidence from atomic force microscopy and an in vivo study.

1 finding

Endothelial ANXA2 functions as a luminal-surface rickettsial adherence receptor, with OmpB as the bacterial ligand.

"We found that deletion of ANXA2 impeded rickettsial attachment to the ECs in vitro and blocked rickettsial adherence to the blood vessel luminal surface in vivo."

PMID:28806774

Fibroblast growth factor receptor-1 mediates internalization of pathogenic spotted fever rickettsiae into host endothelium.

1 finding

FGFR1/heparan-sulfate signaling contributes to pathogenic spotted-fever rickettsial internalization into human microvascular endothelial cells.

"Inhibition of HSPGs by heparinase and FGFRs by AZD4547 (a selective small-molecule inhibitor) results in significant reduction in rickettsial internalization into cultured human microvascular endothelial cells (ECs), which represent the primary targets of pathogenic rickettsiae during human infections."

PMID:29736763

Serum cytokine responses in Rickettsia felis infected febrile children, Ghana.

1 finding

Human R. felis mono-infection is associated with increased serum IL-8, IP-10, MCP-1, MIP-1-alpha, and VEGF in febrile Ghanaian children.

"Levels of IL-8 (interleukin-8), IP-10 (interferon-γ-induced protein-10), MCP-1 (monocyte chemotactic protein-1), MIP-1α (macrophage inflammatory protein-1α) and VEGF (vascular endothelial growth factor) were significantly elevated in R. felis mono-infection"

PMID:12860594

Pathogenic mechanisms of diseases caused by Rickettsia.

1 finding

Review supporting the shared typhus/spotted-fever sequence from dermal rickettsial entry to endothelial dissemination, permeability, edema, and cytotoxic/NK-cell immunity.

"The pathogenetic sequence includes rickettsial entry into the dermis, hematogenous dissemination to vascular endothelial cells"

PMID:9539792

NF-kappa B-dependent inhibition of apoptosis is essential for host cellsurvival during Rickettsia rickettsii infection.

1 finding

Rickettsia rickettsii activates endothelial NF-kappaB to suppress host-cell apoptosis during intracellular infection.

"R. rickettsii, therefore, appeared to inhibit host cell apoptosis via a mechanism dependent on NF-kappa B activation."

PMID:22617213

Contribution of NK cells to the innate phase of host protection against an intracellular bacterium targeting systemic endothelium.

1 finding

NK-cell IFN-gamma and cytotoxicity protect mice against endothelial rickettsial infection and infection-induced thrombosis.

"Together, these findings reveal that NK cells mediate the innate phase of host protection against infection with rickettsiae, most likely via IFN-γ production."

PMID:24188709

Common epidemiology of Rickettsia felis infection and malaria, Africa.

1 finding

R. felis PCR positivity among febrile patients varied geographically and reached 15% in rural Senegal in a 3,122-patient comparison of France, North Africa, and sub-Saharan Africa.

"The risks were lowest in France, Tunisia, and Algeria (1%), and highest in rural Senegal (15%)."

PMID:25706392

Comparison of two quantitative real time PCR assays for Rickettsia detection in patients from Tunisia.

1 finding

Rickettsial duplex qPCR was markedly more often positive from skin biopsies than from whole blood in confirmed Tunisian rickettsiosis.

"Among 44 skin biopsies obtained from patients with confirmed diagnosis, the first duplex was positive in 24 samples (54.5%), with three patients positive by Rtt qPCR."

PMID:24336183

Ribosome-targeting antibiotics and mechanisms of bacterial resistance.

1 finding

Review establishing the bacterial ribosome as a major antibiotic target.

"The ribosome is one of the main antibiotic targets in the bacterial cell."

PMID:18611821

Intracellular organisms.

1 finding

Review supporting intracellular bacterial niches as a reason that poorly cell-penetrant agents can be ineffective.

"The intracellular location of some microorganisms allow them to resist antibiotics with poor ability to penetrate eukaryotic cell membranes, such as the beta-lactam compounds."

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: Flea-Borne Spotted Fever · 2026-09-28T13:58:44Z · View source

Created a new flea-borne spotted fever entry for MONDO:0019364. Ran just research-disorder with Asta requested and explicit fallback to OpenAI, Perplexity, Falcon, and OpenScientist; Asta, OpenAI, Perplexity, and Falcon were unconfigured and OpenScientist produced research/Flea_Borne_Spotted_Fever-deep-research-openscientist.md. Read the report validation: 21 of 21 references resolved, no off-topic references, and no ontology CURIEs suggested. Ran just preflight-dr, which returned SKIP because MONDO records no causal gene for this Rickettsia felis infection. Manually confirmed the report matched the intended R. felis flea-borne spotted fever entity and curated a compact pathograph for the R. felis ribosomal target, obligate intracellular niche, dermal inoculation, endothelial invasion/vascular leak, and R. felis chemokine/VEGF response, with fever, headache, maculopapular rash, eschar, paired-serum serology, and doxycycline treatment. Validated schema, ontology terms, and 20 of 20 evidence snippets.

OpenScientist ▸

Pathophysiology and Clinical Mechanisms of Flea-Borne Spotted Fever

openscientist-autonomous 2026-09-28T06:45:37.096509

Pathophysiology and Clinical Mechanisms of Flea-Borne Spotted Fever

1. Summary (Answer to the Research Question)

Flea-Borne Spotted Fever (FBSF) is an emerging rickettsiosis caused by Rickettsia felis, an atypical, plasmid-bearing spotted-fever-group (SFG) obligate intracellular Gram-negative bacterium transmitted primarily by the cat flea Ctenocephalides felis (with mosquitoes such as Anopheles gambiae as candidate vectors), and epidemiologically entangled with malaria in sub-Saharan Africa. Its core disease mechanism is an endothelial-targeted vasculitis: after dermal inoculation the bacterium adheres to and invades microvascular endothelial cells (OmpB–Annexin A2 adhesion; FGFR1/heparan-sulfate–dependent entry), escapes the phagosome and moves intracellularly by RickA-driven actin polymerization, and subverts host death programs by activating NF-κB to block a masked caspase-8/9/3 apoptotic cascade, allowing replication and cell-to-cell spread. Disseminated endothelial infection produces increased vascular permeability, reactive-oxygen-species (ROS)–mediated oxidative injury, and a procoagulant/platelet-activated state (thromboxane A2, thrombin, endothelin-1) that manifests clinically as fever, headache, maculopapular rash, and—when severe—CNS meningoencephalitis, pleural effusion, and multi-organ failure. A Th1/cytotoxic immune axis (NK and CD8⁺ T cells via IFN-γ, with NK-derived perforin) controls the infection and protects the vasculature, while chemokines (IL-8, IP-10, MCP-1, MIP-1α) and VEGF amplify inflammation and permeability. Doxycycline is the mechanism-based, life-saving first-line therapy.

2. Key Findings (with Statistical/Experimental Evidence)

Etiology, vectors, and epidemiology

R. felis is a distinctive SFG rickettsia with a conjugative plasmid (pRF), diverse-origin genes, and a low optimal growth temperature (<32 °C) [PMID 27155905]. The cat flea is the main reservoir/vector; ~26% of C. felis in Sicily carried R. felis DNA [PMID 25203839]. An. gambiae mosquitoes acquire, maintain (qPCR-positive to day 15), and transmit R. felis by bite (transient rickettsemia in mice) [PMID 26056256].
In Africa, R. felis is a common cause of "fever of unknown origin," with prevalence rising from ~1% (France/N. Africa) to ~15% (rural Senegal) and strong geographic/seasonal correlation with malaria [PMID 24188709].

Molecular and cellular pathways of infection

Adhesion/invasion: Endothelial surface Annexin A2 is the adherence receptor; OmpB is the bacterial ligand (AFM + in vivo) [PMID 31253864]. Internalization requires FGFR1 and heparan-sulfate proteoglycans; heparinase and the FGFR inhibitor AZD4547 reduce entry and lower pulmonary bacterial burden in vivo [PMID 28806774].
Intracellular lifestyle/virulence genes: The genome encodes RickA (Arp2/3 actin nucleator), patatin-like phospholipase, ankyrin/tetratricopeptide effectors, toxin–antitoxin systems, and confirmed beta-lactamase, hemolytic, and actin-motility phenotypes [PMID 15984913, 16481487]; strain diversification tracks arthropod host [PMID 25477419]. mTOR (mTORC1/mTORC2) is activated in infected endothelium [PMID 33003310].
Survival switch: Infection activates NF-κB, which prevents apoptosis of infected endothelium; NF-κB inhibition unmasks apical caspases 8/9 and executioner caspase 3 (mitochondrial cytochrome-c/PARP pathway, peak 12 h), killing infected cells [PMID 9539792, 12819104]. Adr1/Adr2 adhesins evade complement via vitronectin/factor H [PMID 28662039].

Vascular injury and inflammation (effector phase)

Pathogenetic sequence: dermis → hematogenous dissemination → vascular endothelial cells (brain, lung) → increased permeability and edema [PMID 12860594].
Oxidative injury: infected endothelium shows glutathione depletion and increased intracellular peroxide [PMID 9720025].
Procoagulant state: MSF patients show TXA2-dependent platelet activation, thrombin generation, and endothelial dysfunction → vasculitis and microthrombi [PMID 8584998].
Human cytokine signature: R. felis mono-infection significantly elevates IL-8, IP-10, MCP-1, MIP-1α, VEGF [PMID 29736763]; infected macrophages add IL-1β and IL-6 [PMID 11953398].

Protective immunity and severity

NK and CD8⁺ T cells clear rickettsiae via IFN-γ; NK-derived perforin prevents infection-induced thrombosis. NK-deficient mice show impaired clearance, low IFN-γ, and severe hepatic thrombosis [PMID 22617213].

Clinical phenotypes, progression, diagnosis, and treatment

Phenotype: fever, fatigue, headache, maculopapular rash (±eschar); labs show transaminitis, thrombocytopenia, elevated CRP/ESR, hypoalbuminemia [PMID 42715280, 33269795]. Complications: pleural effusion [PMID 42715280], CNS meningoencephalitis (usually >1 week; seizures, meningeal enhancement, pleocytosis) [PMID 39447222], neurological involvement/multi-organ failure [PMID 30419355].
Diagnosis: IFA seroconversion (4-fold IgG rise); skin/eschar qPCR (~48–55% positive) far outperforms whole-blood qPCR (~5–6%) because rickettsemia is low-level [PMID 25706392, 32682398].
Treatment: Doxycycline first-line, given promptly (severe prognosis if delayed) [PMID 30419355]; alternatives azithromycin, rifampicin, fluoroquinolones (documented R. felis response) [PMID 42715280]; doxycycline malaria prophylaxis also protects against R. felis [PMID 24188709].

3. Supported and Refuted Hypotheses

Supported (evidence-backed): 1. FBSF pathology is driven by endothelial infection → vasculitis rather than a secreted toxin. 2. Entry uses defined host receptors (Annexin A2, FGFR1/HSPG) — druggable interfaces. 3. NF-κB anti-apoptosis is essential for the pathogen to sustain its target cell. 4. Tissue damage arises from oxidative + procoagulant endothelial injury amplified by chemokines/VEGF. 5. IFN-γ/perforin (NK, CD8) immunity gates disease severity; deficits → thrombotic/severe disease. 6. Doxycycline efficacy reflects intracellular penetration + protein-synthesis inhibition.

Refuted / not supported: No evidence that FBSF causes damage via a classical exotoxin or via disseminated intravascular coagulation/thrombosis-mediated ischemia as the dominant mechanism (hemostatic mechanisms largely prevent major hemorrhage) [PMID 12860594].

4. Limitations and Future Directions

Much mechanistic detail derives from related SFG species (R. rickettsii, R. conorii, R. parkeri) as models; R. felis-specific in vivo studies remain sparse.
The role of mosquitoes in natural human transmission is unproven; ecology/epidemiology remain incompletely defined.
Eschar frequency and the earliest dermal events for R. felis specifically are under-characterized.
Host-directed therapy (FGFR inhibition, calcium-channel/vascular-barrier modulation, antioxidant/antithrombotic adjuncts) is promising but unproven clinically; one candidate (benidipine) worsened outcomes in a model, underscoring caution.
Future work: R. felis-specific animal models, prospective clinical cohorts distinguishing FBSF from murine typhus and malaria, and biomarker validation (IL-8/VEGF/IP-10) for severity.

Figure: fbsf_pathophysiology_schematic.png — integrated 10-stage mechanistic model.

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Outcome	Count
References checked	21
Resolved	21
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	21
On topic	8
Off topic	0

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Flea-Borne Spotted Fever

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Classifications

Pathophysiology

Pathograph

Phenotypes

Medical Actions

Diagnosis

Prevalence

Infectious Agent

Transmission

Source YAML

References & Deep Research

References

Deep Research

Pathophysiology and Clinical Mechanisms of Flea-Borne Spotted Fever

1. Summary (Answer to the Research Question)

2. Key Findings (with Statistical/Experimental Evidence)

Etiology, vectors, and epidemiology

Molecular and cellular pathways of infection

Vascular injury and inflammation (effector phase)

Protective immunity and severity

Clinical phenotypes, progression, diagnosis, and treatment

3. Supported and Refuted Hypotheses

4. Limitations and Future Directions

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