Rickettsia Parkeri Spotted Fever

🏷

Classifications

Harrison's Part

⚙

Pathophysiology

7

Amblyomma-Borne Rickettsia parkeri Inoculation

A feeding Amblyomma tick inoculates R. parkeri into the dermis, seeding the local infection that precedes the characteristic eschar and disseminated rash.

symbiont entry into host GO:0044409

Downstream

Intracytosolic Rickettsia parkeri Niche Dermal inoculation delivers R. parkeri to cells at the bite site.

Show evidence (1 reference)

PMID:18808353 SUPPORT BACKGROUND Human Clinical

"Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004."

The clinical series names the tick-borne initiating exposure for U.S. R. parkeri disease.

Intracytosolic Rickettsia parkeri Niche

R. parkeri is an obligately intracellular spotted-fever-group Rickettsia that invades host cells and occupies the cytosol, where cell-to-cell spread and persistence require motility proteins and a cell-penetrant antibiotic.

endothelial cell CL:0000115

biological process involved in interaction with host GO:0051701

Downstream

Rickettsial Actin-Based Cell-to-Cell Spread R. parkeri uses host actin assembly to move between infected cells.

Rickettsial Ribosomal Translation (Doxycycline Target) Cytosolic R. parkeri depends on bacterial ribosomal translation.

Show evidence (1 reference)

PMID:19327117 SUPPORT REVIEW SYNTHESIS Other

"Pathogenic Rickettsia species are Gram-negative, obligate intracellular bacteria responsible for the spotted fever and typhus groups of diseases around the world."

The Rickettsia host-cell interaction review establishes the obligate intracellular lifestyle that R. parkeri shares with other pathogenic spotted-fever-group rickettsiae.

Rickettsial Actin-Based Cell-to-Cell Spread

R. parkeri coordinates two actin-based motility modes: early RickA- and Arp2/3-dependent movement with short curved tails, followed by faster Sca2-dependent directional motility with long straight tails that promotes cell-to-cell spread.

actin filament-based movement GO:0030048 Arp2/3 complex-mediated actin nucleation GO:0034314

Downstream

Small-Vessel Rickettsial Vasculitis Rickettsial spread extends local vascular infection and inflammation.

Show evidence (3 references)

PMID:24361066 SUPPORT In Vitro

"Here, we show that each protein directs an independent mode of Rickettsia parkeri motility at different times during infection."

The R. parkeri cell-biology study demonstrates temporally distinct RickA and Sca2 motility phases.

PMID:20972427 SUPPORT In Vitro

"Sca2 nucleates unbranched actin filaments, processively associates with growing barbed ends, requires profilin for efficient elongation, and inhibits the activity of capping protein, all properties shared with formins."

The cell-free and cytoplasmic-extract experiments establish Sca2 as the formin-like actin assembly factor that drives straight-tail Rickettsia motility.

PMID:34423779 SUPPORT Model Organism

"the actin-based motility factor Sca2 is required for dissemination from the skin to internal organs"

Ifnar1/Ifngr1-deficient mouse infections connect Sca2-mediated motility to dissemination from the inoculation site in vivo.

Type I Interferon Restriction of Cytosolic Rickettsiae

Cytosolic R. parkeri is restricted by type I interferon signaling; host-cell inflammasome activity antagonizes the type I interferon response and thereby benefits the pathogen.

type I interferon-mediated signaling pathway GO:0060337

Animal models

Ifnar1/Ifngr1 receptor-deficient R. parkeri mouse Mouse perturbs Ifnar1/Ifngr1 knockout perturbs type I interferon restriction by removing Ifnar1 while also removing the type II interferon receptor.

Downstream

Small-Vessel Rickettsial Vasculitis The balance of interferon restriction and pathogen replication shapes tissue injury.

Show evidence (1 reference)

PMID:32123346 SUPPORT Model Organism

"Here, we report that the human pathogen Rickettsia parkeri is sensitive to IFN-I and benefits from inflammasome-mediated host cell death that antagonizes IFN-I."

Mouse and cell experiments show that type I interferon restricts R. parkeri while inflammasome-dependent cell death counteracts that restriction.

Small-Vessel Rickettsial Vasculitis

Endothelial rickettsial infection injures small blood vessels and increases vascular inflammation and permeability, producing the cutaneous lesions of spotted fever group rickettsioses.

endothelial cell CL:0000115

inflammatory response GO:0006954 ↑ INCREASED

Downstream

Inoculation Eschar Formation Local necrotizing vasculitis at the tick bite produces a tache-noire eschar.

Maculopapular or Vesiculopapular Rash Disseminated cutaneous vascular inflammation produces the exanthem.

Fever Disseminated rickettsial inflammation produces systemic fever.

Headache Systemic inflammatory illness produces headache.

Myalgia Systemic inflammatory illness produces myalgia.

Elevated Hepatic Transaminases Disseminated rickettsial illness can alter hepatic enzymes.

Leukopenia Disseminated rickettsial illness can lower circulating leukocyte counts.

Show evidence (1 reference)

PMID:19327117 SUPPORT REVIEW SYNTHESIS Other

"a majority of sequelae associated with human rickettsioses are the outcome of the pathogen's affinity for endothelium lining the blood vessels"

The pathogenesis review links rickettsial endothelial tropism to vascular inflammation and permeability injury across pathogenic rickettsioses.

Inoculation Eschar Formation

Local R. parkeri infection at the tick-bite site produces a necrotic inoculation eschar surrounded by inflamed dermis.

Animal models

Ifnar1/Ifngr1 receptor-deficient R. parkeri mouse Mouse partially recapitulates Intradermal inoculation of the susceptible mice produces necrotic, inflamed eschars resembling the human bite-site lesion.

Downstream

Inoculation Eschar The necrotic bite-site lesion is clinically visible as an eschar.

Lymphadenopathy Bite-site infection can trigger regional draining lymphadenopathy.

Show evidence (1 reference)

PMID:36693294 SUPPORT REVIEW SYNTHESIS Human Clinical

"Since eschar at the tick bite site has emerged as the main clinical feature of mild R. parkeri infections"

The review establishes the tick-bite inoculation eschar as a central clinical lesion in mild R. parkeri disease.

Rickettsial Ribosomal Translation (Doxycycline Target)

Intracellular R. parkeri depends on bacterial ribosomal translation. Doxycycline and other tetracyclines inhibit the bacterial 30S subunit and arrest spotted-fever-group rickettsial protein synthesis.

Translation GO:0006412 response to antibiotic GO:0046677

Show evidence (1 reference)

PMID:16572105 SUPPORT Human Clinical

"the recommendations for doxycycline are the treatment of choice for both adults and children"

The CDC practice guideline establishes doxycycline as the first-line tetracycline for tick-borne rickettsial diseases.

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Pathograph

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

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Phenotypes

8

Blood 1

Leukopenia Decreased total leukocyte count HP:0001882

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Our results show that at least 60% of R. parkeri cases had altered laboratory parameters, most often showing an increase in transaminases and leukopenia."

The systematic review identifies leukopenia alongside increased transaminases as a frequent laboratory abnormality.

Cardiovascular 1

Lymphadenopathy FREQUENT HP:0002716

Show evidence (1 reference)

PMID:42745336 SUPPORT Human Clinical

"All patients developed symptoms 7-10 days after the bite, including inoculation eschar with progressive enlargement, exanthema, regional lymphadenopathy, fever, myalgia, and prostration"

The outbreak report names regional lymphadenopathy among the symptoms that developed after R. parkeri-infected A. ovale tick bites.

Immune 1

Maculopapular or Vesiculopapular Rash FREQUENT Maculopapular exanthema HP:0040186

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Clinically, more than 60% of the cases had fever (mean of 93%), eschar (mean of 87%), and rash (mean of 68%)."

The systematic review found rash in a mean of 68% of cases.

Integument 1

Inoculation Eschar VERY_FREQUENT Skin ulcer HP:0200042

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Clinically, more than 60% of the cases had fever (mean of 93%), eschar (mean of 87%), and rash (mean of 68%)."

The systematic review found eschars in a mean of 87% of cases.

Metabolism 2

Fever VERY_FREQUENT HP:0001945

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Clinically, more than 60% of the cases had fever (mean of 93%), eschar (mean of 87%), and rash (mean of 68%)."

The systematic review found fever in a mean of 93% of cases.

Elevated Hepatic Transaminases Elevated circulating hepatic transaminase concentration HP:0002910

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Our results show that at least 60% of R. parkeri cases had altered laboratory parameters, most often showing an increase in transaminases and leukopenia."

The systematic review identifies increased transaminases as one of the main laboratory abnormalities across R. parkeri cases.

Nervous System 1

Headache FREQUENT HP:0002315

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Headache and myalgia were predominant nonspecific symptoms (mean of 67% and 61%, respectively)."

The systematic review found headache in a mean of 67% of cases.

Constitutional 1

Myalgia FREQUENT HP:0003326

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Headache and myalgia were predominant nonspecific symptoms (mean of 67% and 61%, respectively)."

The systematic review found myalgia in a mean of 61% of cases.

💊

Medical Actions

3

Empiric doxycycline

Action: Pharmacotherapy NCIT:C15986

Agent: doxycycline CHEBI:50845

Platform: Small molecule

Doxycycline is first-line empiric therapy for suspected R. parkeri spotted fever because it is a cell-penetrant tetracycline that reaches cytosolic rickettsiae and inhibits bacterial protein synthesis.

Mechanism Target:

INHIBITS Rickettsial Ribosomal Translation (Doxycycline Target) — Doxycycline arrests R. parkeri translation at the bacterial ribosome.

BYPASSES Intracytosolic Rickettsia parkeri Niche — Doxycycline penetrates host cells and can reach cytosolic R. parkeri.

Show evidence (1 reference)

PMID:16572105 SUPPORT Human Clinical

"the recommendations for doxycycline are the treatment of choice for both adults and children"

The CDC practice guideline establishes doxycycline as the first-line antibiotic for tick-borne rickettsial diseases in adults and children.

Canine ectoparasite control

Category: Therapeutic Action: canine ectoparasite control Ontology label: Preventive Intervention NCIT:C15843

Platform: Other

In Atlantic rainforest strain foci where A. ovale ticks parasitize dogs, canine ectoparasite control can reduce peridomestic Amblyomma tick exposure and spillover risk.

Show evidence (1 reference)

PMID:35293560 SUPPORT Other

"importance of implementing programs to control canine ectoparasites and to raise awareness of the risks of infection, signs and symptoms of SF caused by R. parkeri strain Atlantic Rainforest."

The report recommends canine ectoparasite-control programs in the context of dog-associated A. ovale detection in an Atlantic rainforest strain R. parkeri focus.

R. parkeri spotted fever risk awareness

Category: Counseling / Informational

Platform: Behavioral / lifestyle

Public awareness of R. parkeri spotted fever infection risks, signs, and symptoms can support prevention and recognition in Atlantic rainforest strain foci.

Show evidence (1 reference)

PMID:35293560 SUPPORT Other

"importance of implementing programs to control canine ectoparasites and to raise awareness of the risks of infection, signs and symptoms of SF caused by R. parkeri strain Atlantic Rainforest."

The report recommends risk-awareness programs in the context of a new Atlantic rainforest strain R. parkeri focus.

🌍

Environmental Factors

1

Amblyomma tick exposure

Bound to ECTO:3000167 exposure to Rickettsia parkeri while keeping preferred_term focused on the Amblyomma acquisition route. `runoak -i sqlite:obo:ecto search 'l~Rickettsia'` returns the species-exact exposure class, while the configured ECTO/XCO sources have no general tick-bite or arthropod-bite exposure term: `l~tick` returns only exposure to Tick-borne encephalitis virus, `l~bite`, `l~arthropod`, and `l~Amblyomma` return no suitable ECTO exposure term, and `runoak -i sqlite:obo:xco search 'l~tick'` returns no XCO term.

Exposure to infected Amblyomma ticks in endemic areas creates the proximate environmental risk for R. parkeri spotted fever.

Show evidence (1 reference)

PMID:18808353 SUPPORT BACKGROUND Human Clinical

"Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004."

The first U.S. case series identifies the Gulf Coast tick as a transmission vector.

Mechanism Target:

TRIGGERS Amblyomma-Borne Rickettsia parkeri Inoculation — An infected Amblyomma tick bite is the acquisition exposure that inoculates R. parkeri into skin.

Show evidence (1 reference)

PMID:18808353 SUPPORT BACKGROUND Human Clinical

"Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004."

The case series establishes Amblyomma tick transmission as the acquisition exposure.

🔬

Diagnosis

1

Eschar-focused clinical diagnosis with molecular confirmation

An inoculation eschar and compatible tick exposure should trigger suspicion, while PCR, immunohistochemistry, culture, and paired serology can confirm spotted-fever-group rickettsiosis and separate R. parkeri from serologically cross-reactive species.

Show evidence (2 references)

PMID:18808353 SUPPORT Human Clinical

"Using indirect immunofluorescence antibody assays, immunohistochemistry, polymerase chain reaction assays, and cell culture isolation, we identified 6 confirmed and 6 probable cases of infection with R. parkeri."

The first U.S. series used serology, immunohistochemistry, PCR and cell culture to classify confirmed and probable cases.

PMID:20404224 SUPPORT Human Clinical

"The SFG rickettsioses share many clinical manifestations and extensive antigenic cross-reactivity that may hamper specific confirmation of the causative agent."

The dermatology case series and review explains why molecular or tissue methods are needed for species-level confirmation.

📈

Progression

1

Acute onset after tick bite

Incubation: 7-10 days

Symptomatic Atlantic rainforest strain cases developed eschar-associated illness 7 to 10 days after the tick bite in the first reported outbreak.

Show evidence (1 reference)

PMID:42745336 SUPPORT Human Clinical

"All patients developed symptoms 7-10 days after the bite, including inoculation eschar with progressive enlargement, exanthema, regional lymphadenopathy, fever, myalgia, and prostration"

The Brazilian Atlantic rainforest spotted fever outbreak report directly dates the post-bite symptom interval.

🌍

Epidemiology

1

Amblyomma-exposed adults in the Americas

R. parkeri spotted fever is reported in the United States and multiple South American countries, with a strong history of tick exposure among recognized cases and a predominance among men aged 18 to 64 years in the published systematic review.

Amblyomma tick exposure male sex adult age

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Overall, our results show that R. parkeri rickettsiosis is more frequent in males in the age group of 18-64 years and that a history of tick exposure was frequent (>90%)."

The systematic review summarizes the demographic and exposure pattern across confirmed and probable cases.

🦠

Infectious Agent

1

Rickettsia parkeri

Obligate intracellular spotted-fever-group Rickettsia species transmitted by Amblyomma ticks in the Americas.

Rickettsia parkeri NCBITaxon:35792

Show evidence (1 reference)

PMID:18808353 SUPPORT BACKGROUND Human Clinical

"Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004."

The first U.S. case-series paper identifies R. parkeri as the etiologic agent and A. maculatum as a vector.

↔️

Transmission

1

Amblyomma tick bite

Infected Amblyomma ticks inoculate R. parkeri into skin while feeding.

Show evidence (1 reference)

PMID:18808353 SUPPORT BACKGROUND Human Clinical

"Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004."

The first U.S. case series identifies the Gulf Coast tick as the U.S. transmission vector.

⚖️

Clinical Burden

Low

Published confirmed and probable cases were usually managed without hospitalization and recovered clinically, consistent with a milder burden than Rocky Mountain spotted fever despite the need for recognition and doxycycline treatment.

Show evidence (1 reference)

PMID:33989945 SUPPORT Human Clinical

"Overall, only 9% of cases required hospitalization and there was a 100% rate of clinical recovery in all of cases."

The systematic review reports low hospitalization and complete recovery among the reviewed R. parkeri cases.

🐁

Animal Models

1

Ifnar1/Ifngr1 receptor-deficient R. parkeri mouse

Intradermal R. parkeri infection of mice lacking both type I and type II interferon receptors produces necrotic, inflamed eschars and disseminated infection, providing a tractable R. parkeri rickettsiosis model in an interferon-susceptible background.

Species

Mouse

Genotype

Ifnar1-/-;Ifngr1-/-

Publication

PMID:34423779

Pathograph links

Type I Interferon Restriction of Cytosolic Rickettsiae perturbs fidelity: moderate Ifnar1/Ifngr1 knockout perturbs type I interferon restriction by removing Ifnar1 while also removing the type II interferon receptor.

Limitations: The model achieves susceptibility by disabling both type I and type II interferon receptor signaling, so it cannot attribute the susceptibility phenotype uniquely to the type I interferon arm; human R. parkeri eschars arise in immunocompetent hosts after natural tick inoculation.

Show evidence (1 reference)

PMID:34423779 SUPPORT Model Organism

"Our results further suggest that discrepancies between mouse and human susceptibility may be due to differences in interferon signaling."

The study interprets mouse resistance versus engineered susceptibility as an interferon-signaling difference, supporting the IFNAR-deficient perturbation link.

Inoculation Eschar Formation partially recapitulates fidelity: moderate Intradermal inoculation of the susceptible mice produces necrotic, inflamed eschars resembling the human bite-site lesion.

Limitations: The model recapitulates eschar formation only in a genetically interferon-receptor-deficient mouse and progresses to disseminated lethal disease, whereas human R. parkeri eschars arise in immunocompetent hosts in a typically non-lethal illness after natural tick inoculation.

Show evidence (1 reference)

PMID:34423779 SUPPORT Model Organism

"Similar to human infection, eschars exhibited necrosis and inflammation, with bacteria primarily found in leukocytes."

The study directly compares the model eschar to the necrotic, inflamed human lesion.

{ }

Source YAML

click to show

name: Rickettsia Parkeri Spotted Fever
creation_date: "2026-09-27T23:51:00Z"
category: Infectious Disease
description: >-
Rickettsia parkeri spotted fever is an acute Amblyomma tick-borne spotted
fever group rickettsiosis caused by the obligately intracellular bacterium
Rickettsia parkeri. After inoculation into skin, R. parkeri invades host cells,
escapes to the cytosol, and uses RickA- and Sca2-driven actin motility to
spread cell to cell. The clinical syndrome is typically milder than Rocky
Mountain spotted fever and is marked by an inoculation eschar, fever,
maculopapular or vesiculopapular rash, headache, myalgia, and regional
lymphadenopathy; systemic vascular injury is usually limited, and reported
cases recover with tetracycline-class therapy.
disease_term:
preferred_term: Rickettsia parkeri spotted fever
term:
id: MONDO:0000234
label: Rickettsia parkeri spotted fever
parents:
- Spotted fever rickettsiosis
synonyms:
- Rickettsia parkeri rickettsiosis
- R. parkeri spotted fever
- Tidewater spotted fever
- American boutonneuse fever
- Atlantic rainforest spotted fever

classifications:
harrisons_chapter:
- classification_value: INFECTIOUS_DISEASES
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Rickettsia parkeri rickettsiosis is recognized as the second most
prevalent tick-borne disease caused by spotted fever group rickettsiae
in the Americas
explanation: >-
The systematic review frames R. parkeri spotted fever as a bacterial
tick-borne spotted-fever-group rickettsiosis, placing it in Harrison's
Infectious Diseases Part.

infectious_agent:
- name: Rickettsia parkeri
infectious_agent_term:
preferred_term: Rickettsia parkeri
term:
id: NCBITaxon:35792
label: Rickettsia parkeri
description: >-
Obligate intracellular spotted-fever-group Rickettsia species transmitted by
Amblyomma ticks in the Americas.
evidence:
- reference: PMID:18808353
reference_title: Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
Rickettsia parkeri rickettsiosis, a recently identified spotted fever
transmitted by the Gulf Coast tick (Amblyomma maculatum), was first
described in 2004.
explanation: >-
The first U.S. case-series paper identifies R. parkeri as the etiologic
agent and A. maculatum as a vector.

agent_life_cycle:
description: >-
R. parkeri is maintained in Amblyomma ticks that transmit the organism to
humans during blood feeding. Humans are incidental hosts; the Gulf Coast tick
A. maculatum transmits U.S. cases, A. ovale transmits Atlantic rainforest
strain infections in Brazil, and A. triste and A. tigrinum are associated
with Argentine transmission.
hosts:
- preferred_term: Homo sapiens
role: incidental clinical host
term:
id: NCBITaxon:9606
label: Homo sapiens
- preferred_term: Amblyomma maculatum
role: Gulf Coast tick vector and reservoir host
term:
id: NCBITaxon:34609
label: Amblyomma maculatum
- preferred_term: Amblyomma ovale
role: Atlantic rainforest strain vector host
term:
id: NCBITaxon:208206
label: Amblyomma ovale
- preferred_term: Amblyomma triste
role: South American vector host
term:
id: NCBITaxon:251400
label: Amblyomma triste
- preferred_term: Amblyomma tigrinum
role: South American vector host
term:
id: NCBITaxon:251399
label: Amblyomma tigrinum
vectors:
- Amblyomma maculatum (Gulf Coast tick)
- Amblyomma ovale
- Amblyomma triste
- Amblyomma tigrinum
evidence:
- reference: PMID:36693294
reference_title: "The inoculation eschar of Rickettsia parkeri rickettsiosis in Brazil: Importance and cautions."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Rickettsia parkeri strain Atlantic rainforest infections transmitted by
adult Amblyomma ovale ticks cause a milder non-lethal febrile disease with
an eschar (necrosis) at the tick bite site.
explanation: >-
The Brazilian review identifies A. ovale as a vector for Atlantic
rainforest strain R. parkeri infections.
- reference: PMID:30928146
reference_title: "[Spotted fever in Argentina. Description of two clinical cases]."
supports: SUPPORT
evidence_source: OTHER
quote_role: BACKGROUND
snippet: >-
Amblyomma triste acts as a vector; and the provinces of Córdoba, La Rioja,
San Luis and La Pampa where Amblyomma tigrinum is the vector.
explanation: >-
The Argentine case report and review identify A. triste and A. tigrinum as
vectors in R. parkeri epidemiologic settings.

transmission:
- name: Amblyomma tick bite
description: >-
Infected Amblyomma ticks inoculate R. parkeri into skin while feeding.
evidence:
- reference: PMID:18808353
reference_title: Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
Rickettsia parkeri rickettsiosis, a recently identified spotted fever
transmitted by the Gulf Coast tick (Amblyomma maculatum), was first
described in 2004.
explanation: >-
The first U.S. case series identifies the Gulf Coast tick as the U.S.
transmission vector.

epidemiology:
- name: Amblyomma-exposed adults in the Americas
description: >-
R. parkeri spotted fever is reported in the United States and multiple South
American countries, with a strong history of tick exposure among recognized
cases and a predominance among men aged 18 to 64 years in the published
systematic review.
factors:
- Amblyomma tick exposure
- male sex
- adult age
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Overall, our results show that R. parkeri rickettsiosis is more frequent
in males in the age group of 18-64 years and that a history of tick
exposure was frequent (>90%).
explanation: >-
The systematic review summarizes the demographic and exposure pattern
across confirmed and probable cases.

progression:
- phase: Acute onset after tick bite
incubation_days: 7-10
notes: >-
Symptomatic Atlantic rainforest strain cases developed eschar-associated
illness 7 to 10 days after the tick bite in the first reported outbreak.
evidence:
- reference: PMID:42745336
reference_title: "Short Report: First Outbreak of Atlantic Rainforest Spotted Fever in North-Eastern of Brazil-Clinical Features and Eco-Epidemiological Investigation."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients developed symptoms 7-10 days after the bite, including
inoculation eschar with progressive enlargement, exanthema, regional
lymphadenopathy, fever, myalgia, and prostration
explanation: >-
The Brazilian Atlantic rainforest spotted fever outbreak report directly
dates the post-bite symptom interval.

clinical_burden:
burden_level: LOW
rationale: >-
Published confirmed and probable cases were usually managed without
hospitalization and recovered clinically, consistent with a milder burden
than Rocky Mountain spotted fever despite the need for recognition and
doxycycline treatment.
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Overall, only 9% of cases required hospitalization and there was a 100%
rate of clinical recovery in all of cases.
explanation: >-
The systematic review reports low hospitalization and complete recovery
among the reviewed R. parkeri cases.

pathophysiology:
- name: Amblyomma-Borne Rickettsia parkeri Inoculation
role: trigger
biological_scale: ORGANISM
description: >-
A feeding Amblyomma tick inoculates R. parkeri into the dermis, seeding the
local infection that precedes the characteristic eschar and disseminated rash.
biological_processes:
- preferred_term: symbiont entry into host
term:
id: GO:0044409
label: symbiont entry into host
downstream:
- target: Intracytosolic Rickettsia parkeri Niche
causal_link_type: DIRECT
description: Dermal inoculation delivers R. parkeri to cells at the bite site.
evidence:
- reference: PMID:18808353
reference_title: Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
Rickettsia parkeri rickettsiosis, a recently identified spotted fever
transmitted by the Gulf Coast tick (Amblyomma maculatum), was first
described in 2004.
explanation: >-
The clinical series names the tick-borne initiating exposure for U.S. R.
parkeri disease.

- name: Intracytosolic Rickettsia parkeri Niche
role: primary_infection
conforms_to: >-
intracellular_pathogen_persistence#Intracellular Niche and Beta-Lactam
Exclusion
biological_scale: CELLULAR
description: >-
R. parkeri is an obligately intracellular spotted-fever-group Rickettsia
that invades host cells and occupies the cytosol, where cell-to-cell spread
and persistence require motility proteins and a cell-penetrant antibiotic.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: biological process involved in interaction with host
term:
id: GO:0051701
label: biological process involved in interaction with host
downstream:
- target: Rickettsial Actin-Based Cell-to-Cell Spread
causal_link_type: DIRECT
description: R. parkeri uses host actin assembly to move between infected cells.
- target: Rickettsial Ribosomal Translation (Doxycycline Target)
causal_link_type: DIRECT
description: Cytosolic R. parkeri depends on bacterial ribosomal translation.
evidence:
- reference: PMID:19327117
reference_title: Host-cell interactions with pathogenic Rickettsia species.
supports: SUPPORT
evidence_source: OTHER
quote_role: REVIEW_SYNTHESIS
snippet: >-
Pathogenic Rickettsia species are Gram-negative, obligate intracellular
bacteria responsible for the spotted fever and typhus groups of diseases
around the world.
explanation: >-
The Rickettsia host-cell interaction review establishes the obligate
intracellular lifestyle that R. parkeri shares with other pathogenic
spotted-fever-group rickettsiae.

- name: Rickettsial Actin-Based Cell-to-Cell Spread
role: primary_infection
biological_scale: CELLULAR
description: >-
R. parkeri coordinates two actin-based motility modes: early RickA- and
Arp2/3-dependent movement with short curved tails, followed by faster
Sca2-dependent directional motility with long straight tails that promotes
cell-to-cell spread.
biological_processes:
- preferred_term: actin filament-based movement
term:
id: GO:0030048
label: actin filament-based movement
- preferred_term: Arp2/3 complex-mediated actin nucleation
term:
id: GO:0034314
label: Arp2/3 complex-mediated actin nucleation
downstream:
- target: Small-Vessel Rickettsial Vasculitis
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Rickettsial spread extends local vascular infection and inflammation.
evidence:
- reference: PMID:24361066
reference_title: Rickettsia actin-based motility occurs in distinct phases mediated by different actin nucleators.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Here, we show that each protein directs an independent mode of Rickettsia
parkeri motility at different times during infection.
explanation: >-
The R. parkeri cell-biology study demonstrates temporally distinct RickA
and Sca2 motility phases.
- reference: PMID:20972427
reference_title: Rickettsia Sca2 is a bacterial formin-like mediator of actin-based motility.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Sca2 nucleates unbranched actin filaments, processively associates with
growing barbed ends, requires profilin for efficient elongation, and
inhibits the activity of capping protein, all properties shared with
formins.
explanation: >-
The cell-free and cytoplasmic-extract experiments establish Sca2 as the
formin-like actin assembly factor that drives straight-tail Rickettsia
motility.
- reference: PMID:34423779
reference_title: Interferon receptor-deficient mice are susceptible to eschar-associated rickettsiosis.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
the actin-based motility factor Sca2 is required for dissemination from
the skin to internal organs
explanation: >-
Ifnar1/Ifngr1-deficient mouse infections connect Sca2-mediated motility
to dissemination from the inoculation site in vivo.

- name: Type I Interferon Restriction of Cytosolic Rickettsiae
role: immune_response
biological_scale: CELLULAR
description: >-
Cytosolic R. parkeri is restricted by type I interferon signaling; host-cell
inflammasome activity antagonizes the type I interferon response and thereby
benefits the pathogen.
biological_processes:
- preferred_term: type I interferon-mediated signaling pathway
term:
id: GO:0060337
label: type I interferon-mediated signaling pathway
downstream:
- target: Small-Vessel Rickettsial Vasculitis
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: The balance of interferon restriction and pathogen replication shapes tissue injury.
evidence:
- reference: PMID:32123346
reference_title: Inflammasome-mediated antagonism of type I interferon enhances Rickettsia pathogenesis.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Here, we report that the human pathogen Rickettsia parkeri is sensitive to
IFN-I and benefits from inflammasome-mediated host cell death that
antagonizes IFN-I.
explanation: >-
Mouse and cell experiments show that type I interferon restricts R.
parkeri while inflammasome-dependent cell death counteracts that
restriction.

- name: Small-Vessel Rickettsial Vasculitis
role: vascular_response
biological_scale: TISSUE
description: >-
Endothelial rickettsial infection injures small blood vessels and increases
vascular inflammation and permeability, producing the cutaneous lesions of
spotted fever group rickettsioses.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: inflammatory response
term:
id: GO:0006954
label: inflammatory response
modifier: INCREASED
downstream:
- target: Inoculation Eschar Formation
causal_link_type: DIRECT
description: Local necrotizing vasculitis at the tick bite produces a tache-noire eschar.
- target: Maculopapular or Vesiculopapular Rash
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Disseminated cutaneous vascular inflammation produces the exanthem.
- target: Fever
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Disseminated rickettsial inflammation produces systemic fever.
- target: Headache
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Systemic inflammatory illness produces headache.
- target: Myalgia
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Systemic inflammatory illness produces myalgia.
- target: Elevated Hepatic Transaminases
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Disseminated rickettsial illness can alter hepatic enzymes.
- target: Leukopenia
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Disseminated rickettsial illness can lower circulating leukocyte counts.
evidence:
- reference: PMID:19327117
reference_title: Host-cell interactions with pathogenic Rickettsia species.
supports: SUPPORT
evidence_source: OTHER
quote_role: REVIEW_SYNTHESIS
snippet: >-
a majority of sequelae associated with human rickettsioses are the outcome
of the pathogen's affinity for endothelium lining the blood vessels
explanation: >-
The pathogenesis review links rickettsial endothelial tropism to vascular
inflammation and permeability injury across pathogenic rickettsioses.

- name: Inoculation Eschar Formation
role: tissue_damage
biological_scale: TISSUE
description: >-
Local R. parkeri infection at the tick-bite site produces a necrotic
inoculation eschar surrounded by inflamed dermis.
downstream:
- target: Inoculation Eschar
causal_link_type: DIRECT
description: The necrotic bite-site lesion is clinically visible as an eschar.
- target: Lymphadenopathy
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Bite-site infection can trigger regional draining lymphadenopathy.
evidence:
- reference: PMID:36693294
reference_title: "The inoculation eschar of Rickettsia parkeri rickettsiosis in Brazil: Importance and cautions."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Since eschar at the tick bite site has emerged as the main clinical
feature of mild R. parkeri infections
explanation: >-
The review establishes the tick-bite inoculation eschar as a central
clinical lesion in mild R. parkeri disease.

- name: Rickettsial Ribosomal Translation (Doxycycline Target)
role: therapeutic_vulnerability
conforms_to: "bacterial_protein_synthesis_inhibition#Bacterial mRNA Translation by the Ribosome"
biological_scale: MOLECULAR
description: >-
Intracellular R. parkeri depends on bacterial ribosomal translation.
Doxycycline and other tetracyclines inhibit the bacterial 30S subunit and
arrest spotted-fever-group rickettsial protein synthesis.
biological_processes:
- preferred_term: Translation
term:
id: GO:0006412
label: translation
- preferred_term: response to antibiotic
term:
id: GO:0046677
label: response to antibiotic
evidence:
- reference: PMID:16572105
reference_title: >-
Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain
spotted fever, ehrlichioses, and anaplasmosis--United States: a practical
guide for physicians and other health-care and public health
professionals.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the recommendations for doxycycline are the treatment of choice for both
adults and children
explanation: >-
The CDC practice guideline establishes doxycycline as the first-line
tetracycline for tick-borne rickettsial diseases.

phenotypes:
- name: Inoculation Eschar
category: Dermatologic
frequency: VERY_FREQUENT
diagnostic: true
description: >-
A necrotic tache-noire skin ulcer at the tick-bite site is the hallmark
lesion of R. parkeri spotted fever and helps separate this disease from
Rocky Mountain spotted fever.
phenotype_term:
preferred_term: Skin ulcer
term:
id: HP:0200042
label: Skin ulcer
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Clinically, more than 60% of the cases had fever (mean of 93%), eschar
(mean of 87%), and rash (mean of 68%).
explanation: The systematic review found eschars in a mean of 87% of cases.

- name: Fever
category: Constitutional
frequency: VERY_FREQUENT
description: Fever is the most frequent systemic symptom of R. parkeri spotted fever.
phenotype_term:
preferred_term: Fever
term:
id: HP:0001945
label: Fever
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Clinically, more than 60% of the cases had fever (mean of 93%), eschar
(mean of 87%), and rash (mean of 68%).
explanation: The systematic review found fever in a mean of 93% of cases.

- name: Maculopapular or Vesiculopapular Rash
category: Dermatologic
frequency: FREQUENT
description: >-
The disseminated rash is commonly maculopapular and can be vesiculopapular.
phenotype_term:
preferred_term: Maculopapular exanthema
term:
id: HP:0040186
label: Maculopapular exanthema
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Clinically, more than 60% of the cases had fever (mean of 93%), eschar
(mean of 87%), and rash (mean of 68%).
explanation: The systematic review found rash in a mean of 68% of cases.

- name: Headache
category: Neurologic
frequency: FREQUENT
description: Headache is one of the main nonspecific symptoms.
phenotype_term:
preferred_term: Headache
term:
id: HP:0002315
label: Headache
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Headache and myalgia were predominant nonspecific symptoms (mean of 67% and 61%, respectively).
explanation: The systematic review found headache in a mean of 67% of cases.

- name: Myalgia
category: Musculoskeletal
frequency: FREQUENT
description: Myalgia is a frequent nonspecific symptom.
phenotype_term:
preferred_term: Myalgia
term:
id: HP:0003326
label: Myalgia
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Headache and myalgia were predominant nonspecific symptoms (mean of 67% and 61%, respectively).
explanation: The systematic review found myalgia in a mean of 61% of cases.

- name: Elevated Hepatic Transaminases
category: Laboratory
description: Elevated transaminases are among the common laboratory abnormalities.
phenotype_term:
preferred_term: Elevated circulating hepatic transaminase concentration
term:
id: HP:0002910
label: Elevated circulating hepatic transaminase concentration
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Our results show that at least 60% of R. parkeri cases had altered
laboratory parameters, most often showing an increase in transaminases and
leukopenia.
explanation: >-
The systematic review identifies increased transaminases as one of the
main laboratory abnormalities across R. parkeri cases.

- name: Leukopenia
category: Hematologic
description: Leukopenia is among the common laboratory abnormalities.
phenotype_term:
preferred_term: Leukopenia
term:
id: HP:0001882
label: Decreased total leukocyte count
evidence:
- reference: PMID:33989945
reference_title: "Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Our results show that at least 60% of R. parkeri cases had altered
laboratory parameters, most often showing an increase in transaminases and
leukopenia.
explanation: >-
The systematic review identifies leukopenia alongside increased
transaminases as a frequent laboratory abnormality.

- name: Lymphadenopathy
category: Lymphatic
frequency: FREQUENT
description: Regional lymphadenopathy is part of the eschar-associated febrile syndrome.
phenotype_term:
preferred_term: Lymphadenopathy
term:
id: HP:0002716
label: Lymphadenopathy
evidence:
- reference: PMID:42745336
reference_title: "Short Report: First Outbreak of Atlantic Rainforest Spotted Fever in North-Eastern of Brazil-Clinical Features and Eco-Epidemiological Investigation."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients developed symptoms 7-10 days after the bite, including
inoculation eschar with progressive enlargement, exanthema, regional
lymphadenopathy, fever, myalgia, and prostration
explanation: >-
The outbreak report names regional lymphadenopathy among the symptoms
that developed after R. parkeri-infected A. ovale tick bites.

diagnosis:
- name: Eschar-focused clinical diagnosis with molecular confirmation
description: >-
An inoculation eschar and compatible tick exposure should trigger suspicion,
while PCR, immunohistochemistry, culture, and paired serology can confirm
spotted-fever-group rickettsiosis and separate R. parkeri from
serologically cross-reactive species.
evidence:
- reference: PMID:18808353
reference_title: Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Using indirect immunofluorescence antibody assays,
immunohistochemistry, polymerase chain reaction assays, and cell culture
isolation, we identified 6 confirmed and 6 probable cases of infection
with R. parkeri.
explanation: >-
The first U.S. series used serology, immunohistochemistry, PCR and cell
culture to classify confirmed and probable cases.
- reference: PMID:20404224
reference_title: The expanding spectrum of eschar-associated rickettsioses in the United States.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The SFG rickettsioses share many clinical manifestations and extensive
antigenic cross-reactivity that may hamper specific confirmation of the
causative agent.
explanation: >-
The dermatology case series and review explains why molecular or tissue
methods are needed for species-level confirmation.

environmental:
- name: Amblyomma tick exposure
exposure_term:
preferred_term: Amblyomma tick exposure
term:
id: ECTO:3000167
label: exposure to Rickettsia parkeri
influences_mechanisms:
- target: Amblyomma-Borne Rickettsia parkeri Inoculation
environmental_effect: TRIGGERS
causal_link_type: DIRECT
description: >-
An infected Amblyomma tick bite is the acquisition exposure that inoculates
R. parkeri into skin.
evidence:
- reference: PMID:18808353
reference_title: Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
Rickettsia parkeri rickettsiosis, a recently identified spotted fever
transmitted by the Gulf Coast tick (Amblyomma maculatum), was first
described in 2004.
explanation: The case series establishes Amblyomma tick transmission as the acquisition exposure.
description: >-
Exposure to infected Amblyomma ticks in endemic areas creates the proximate
environmental risk for R. parkeri spotted fever.
effect: Increases risk of R. parkeri infection by exposing skin to infected Amblyomma bites.
evidence:
- reference: PMID:18808353
reference_title: Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
Rickettsia parkeri rickettsiosis, a recently identified spotted fever
transmitted by the Gulf Coast tick (Amblyomma maculatum), was first
described in 2004.
explanation: The first U.S. case series identifies the Gulf Coast tick as a transmission vector.
notes: >-
Bound to ECTO:3000167 exposure to Rickettsia parkeri while keeping
preferred_term focused on the Amblyomma acquisition route. `runoak -i
sqlite:obo:ecto search 'l~Rickettsia'` returns the species-exact exposure
class, while the configured ECTO/XCO sources have no general tick-bite or
arthropod-bite exposure term: `l~tick` returns only exposure to Tick-borne
encephalitis virus, `l~bite`, `l~arthropod`, and `l~Amblyomma` return no
suitable ECTO exposure term, and `runoak -i sqlite:obo:xco search
'l~tick'` returns no XCO term.

animal_models:
- name: Ifnar1/Ifngr1 receptor-deficient R. parkeri mouse
species: Mouse
genotype: Ifnar1-/-;Ifngr1-/-
description: >-
Intradermal R. parkeri infection of mice lacking both type I and type II
interferon receptors produces necrotic, inflamed eschars and disseminated
infection, providing a tractable R. parkeri rickettsiosis model in an
interferon-susceptible background.
publication: PMID:34423779
modeled_mechanisms:
- target: Type I Interferon Restriction of Cytosolic Rickettsiae
relationship: PERTURBS
fidelity: MODERATE
description: >-
Ifnar1/Ifngr1 knockout perturbs type I interferon restriction by removing
Ifnar1 while also removing the type II interferon receptor.
limitations: >-
The model achieves susceptibility by disabling both type I and type II
interferon receptor signaling, so it cannot attribute the susceptibility
phenotype uniquely to the type I interferon arm; human R. parkeri eschars
arise in immunocompetent hosts after natural tick inoculation.
evidence:
- reference: PMID:34423779
reference_title: Interferon receptor-deficient mice are susceptible to eschar-associated rickettsiosis.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Our results further suggest that discrepancies between mouse and human
susceptibility may be due to differences in interferon signaling.
explanation: >-
The study interprets mouse resistance versus engineered susceptibility
as an interferon-signaling difference, supporting the IFNAR-deficient
perturbation link.
- target: Inoculation Eschar Formation
relationship: PARTIALLY_RECAPITULATES
fidelity: MODERATE
description: >-
Intradermal inoculation of the susceptible mice produces necrotic,
inflamed eschars resembling the human bite-site lesion.
limitations: >-
The model recapitulates eschar formation only in a genetically
interferon-receptor-deficient mouse and progresses to disseminated lethal
disease, whereas human R. parkeri eschars arise in immunocompetent hosts
in a typically non-lethal illness after natural tick inoculation.
evidence:
- reference: PMID:34423779
reference_title: Interferon receptor-deficient mice are susceptible to eschar-associated rickettsiosis.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Similar to human infection, eschars exhibited necrosis and inflammation,
with bacteria primarily found in leukocytes.
explanation: >-
The study directly compares the model eschar to the necrotic,
inflamed human lesion.

treatments:
- name: Empiric doxycycline
description: >-
Doxycycline is first-line empiric therapy for suspected R. parkeri spotted
fever because it is a cell-penetrant tetracycline that reaches cytosolic
rickettsiae and inhibits bacterial protein synthesis.
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 (Doxycycline Target)
treatment_effect: INHIBITS
description: Doxycycline arrests R. parkeri translation at the bacterial ribosome.
- target: Intracytosolic Rickettsia parkeri Niche
treatment_effect: BYPASSES
description: Doxycycline penetrates host cells and can reach cytosolic R. parkeri.
evidence:
- reference: PMID:16572105
reference_title: >-
Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain
spotted fever, ehrlichioses, and anaplasmosis--United States: a practical
guide for physicians and other health-care and public health
professionals.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the recommendations for doxycycline are the treatment of choice for both
adults and children
explanation: >-
The CDC practice guideline establishes doxycycline as the first-line
antibiotic for tick-borne rickettsial diseases in adults and children.

- name: Canine ectoparasite control
description: >-
In Atlantic rainforest strain foci where A. ovale ticks parasitize dogs,
canine ectoparasite control can reduce peridomestic Amblyomma tick
exposure and spillover risk.
action_category: THERAPEUTIC
therapeutic_modality: OTHER
treatment_term:
preferred_term: canine ectoparasite control
term:
id: NCIT:C15843
label: Preventive Intervention
evidence:
- reference: PMID:35293560
reference_title: A new focus of spotted fever caused by Rickettsia parkeri in Brazil.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
importance of implementing programs to control canine ectoparasites and to
raise awareness of the risks of infection, signs and symptoms of SF caused
by R. parkeri strain Atlantic Rainforest.
explanation: >-
The report recommends canine ectoparasite-control programs in the context
of dog-associated A. ovale detection in an Atlantic rainforest strain R.
parkeri focus.

- name: R. parkeri spotted fever risk awareness
description: >-
Public awareness of R. parkeri spotted fever infection risks, signs, and
symptoms can support prevention and recognition in Atlantic rainforest
strain foci.
action_category: COUNSELING_INFORMATIONAL
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: community R. parkeri risk awareness
notes: >-
NCIT has no specific clinical-intervention term for community awareness
campaigns about R. parkeri spotted fever risk in a tick focus.
evidence:
- reference: PMID:35293560
reference_title: A new focus of spotted fever caused by Rickettsia parkeri in Brazil.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
importance of implementing programs to control canine ectoparasites and to
raise awareness of the risks of infection, signs and symptoms of SF caused
by R. parkeri strain Atlantic Rainforest.
explanation: >-
The report recommends risk-awareness programs in the context of a new
Atlantic rainforest strain R. parkeri focus.

review_notes: >-
Curated from
research/Rickettsia_Parkeri_Spotted_Fever-deep-research-openscientist.md.
The report's only term-validation warning was a benign MONDO label mismatch:
the report used the disease synonym "Rickettsia parkeri rickettsiosis" for
MONDO:0000234, whose canonical MONDO label is "Rickettsia parkeri spotted
fever".

📚

References & Deep Research

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 (2)

Record review notes

Curated from research/Rickettsia_Parkeri_Spotted_Fever-deep-research-openscientist.md. The report's only term-validation warning was a benign MONDO label mismatch: the report used the disease synonym "Rickettsia parkeri rickettsiosis" for MONDO:0000234, whose canonical MONDO label is "Rickettsia parkeri spotted fever".

Create: Rickettsia parkeri spotted fever · 2026-09-28T00:17:37Z · View source

Created a de novo Rickettsia parkeri spotted fever entry from the OpenScientist deep-research report at research/Rickettsia_Parkeri_Spotted_Fever-deep-research-openscientist.md after Falcon fell back because EDISON_API_KEY was unavailable. Curated the R. parkeri agent and Amblyomma vector ecology, the tick-borne intracytosolic rickettsial mechanism with actin-based spread and type I interferon restriction, the main fever-eschar-rash phenotype profile from the systematic review, species-aware diagnosis, and empiric doxycycline therapy.

OpenScientist ▸

Key Findings

openscientist-autonomous 24 citations 2026-09-27T17:07:49.644125

Key Findings

1. Clinical profile: an eschar-associated febrile illness milder than RMSF (F001)

The defining clinical portrait of R. parkeri rickettsiosis comes from a systematic review of 77 clinical cases (32 confirmed, 45 probable). Pooled phenotype frequencies were: fever ~93%, eschar ~87%, rash ~68%, headache ~67%, myalgia ~61%, with ≥60% of cases showing altered laboratory parameters (PMID: 33989945):

"more than 60% of the cases had fever (mean of 93%), eschar (mean of 87%), and rash (mean of 68%). Headache and myalgia were predominant nonspecific symptoms (mean of 67% and 61%, respectively)"

The first 12 US cases (6 confirmed, 6 probable) established the disease as clinically distinct from — and milder than — RMSF (PMID: 18808353):

"The aggregate clinical characteristics of these patients revealed a disease similar to but less severe than classically described Rocky Mountain spotted fever."

It is the second most prevalent SFG rickettsiosis in the Americas.

Suggested HPO terms: Fever (HP:0001945), Skin ulcer/eschar (HP:0200042), Maculopapular exanthem/abnormality of the skin (HP:0000988), Lymphadenopathy (HP:0002716), Headache (HP:0002315), Myalgia (HP:0003326), Thrombocytopenia (HP:0001873), Elevated hepatic transaminases (HP:0002910), Lymphopenia (HP:0001888).

2. Vector biology and strain geography (F002)

R. parkeri exists as pathogenic strains with distinct vector–geography pairings:

Strain	Primary vector	Geography	Clinical note
R. parkeri sensu stricto	Amblyomma maculatum (Gulf Coast tick)	Southeastern/South-central USA	First human case 2004
Strain Atlantic rainforest	Amblyomma ovale	Brazil / South America	Milder, non-lethal, eschar
(regional)	Amblyomma triste, A. tigrinum	Argentina, Uruguay	Benign course

The Atlantic rainforest strain is explicitly characterized as causing "a milder non-lethal febrile disease with an eschar (necrosis) at the tick bite site" (PMID: 36693294). Vector range is expanding northward: A. maculatum + R. parkeri are now established in Ohio (PMID: 42661358) —

"We report the establishment of the Gulf Coast tick (Amblyomma maculatum) and Rickettsia parkeri bacteria in Ohio, USA."

— and in southern Illinois, where R. parkeri infection prevalence in A. maculatum reached 16.4% (PMID: 42314659). Laboratory competence has also been shown for A. americanum and Dermacentor variabilis (PMID: 41749360). Dogs serve as sentinel hosts.

3. Core pathophysiology: endothelial infection and two-phase actin-based motility (F003)

R. parkeri is an obligate intracellular Gram-negative bacterium with tropism for vascular endothelium. Infection produces vascular inflammation, loss of vascular integrity, and increased permeability — collectively "rickettsial vasculitis" (PMID: 19327117):

"the pathogen's affinity for endothelium lining the blood vessels, the consequences of which are vascular inflammation, insult to vascular integrity and compromised vascular permeability, collectively termed 'Rickettsial vasculitis'"

Intracellularly, R. parkeri escapes the phagosome into the cytoplasm and drives actin-based motility in two temporally distinct phases (PMID: 24361066):

"each protein directs an independent mode of Rickettsia parkeri motility at different times during infection. Early after invasion, motility is slow and meandering, generating short, curved actin tails that are enriched with Arp2/3 complex and cofilin"

Early motility is driven by RickA activating the host Arp2/3 complex; late, fast, directionally persistent motility requires Sca2, a functional mimic of eukaryotic formins (PMID: 20972427):

"Sca2 nucleates unbranched actin filaments, processively associates with growing barbed ends, requires profilin for efficient elongation, and inhibits the activity of capping protein, all properties shared with formins"

Structural work (cryo-EM) shows Sca2 forms a formin-FH2-like doughnut core (PMID: 37028467), and comparative studies reveal divergent motility mechanisms across Rickettsia species (e.g., R. bellii Sca2/6; PMID: 42048062).

Suggested GO/CL terms: actin nucleation (GO:0045010), Arp2/3 complex-mediated actin nucleation (GO:0034314), actin filament-based movement (GO:0030048), host cell cytoplasm (GO:0030430), endothelial cell (CL:0000115).

4. Immune mechanism: type I interferon is protective (F004)

Innate immunity controls R. parkeri infection. Interferon α/β receptor-deficient mice (and combined IFN-receptor-deficient mice) are susceptible and develop eschar-associated rickettsiosis, whereas immunocompetent wild-type mice are largely resistant (PMID: 34423779):

"Interferon receptor-deficient mice are susceptible to eschar-associated rickettsiosis"

The bacterium in turn antagonizes type I interferon via inflammasome activity, and this antagonism enhances pathogenesis (PMID: 32123346):

"Inflammasome-mediated antagonism of type I interferon enhances Rickettsia pathogenesis"

This host–pathogen cross-talk (interferons + inflammasomes) determines the balance between control and disease.

Suggested GO terms: type I interferon signaling pathway (GO:0060337), response to interferon-alpha (GO:0035455), inflammasome complex (GO:0061702).

5. Diagnosis and treatment (F005)

Doxycycline is the treatment of choice for SFG rickettsioses in both adults and children, and early empiric therapy prevents severe morbidity and death (PMID: 16572105):

"the recommendations for doxycycline are the treatment of choice for both adults and children"

R. parkeri cases respond uniformly and promptly. Diagnosis relies on: (1) recognition of the inoculation eschar; (2) indirect immunofluorescence antibody assay (IFA) demonstrating seroconversion / ≥4-fold titer rise; (3) PCR of eschar crust or skin biopsy targeting ompA, gltA, ompB; (4) immunohistochemistry; and (5) cell-culture isolation (PMID: 18808353):

"Using indirect immunofluorescence antibody assays, immunohistochemistry, polymerase chain reaction assays, and cell culture isolation, we identified 6 confirmed and 6 probable cases of infection with R. parkeri."

Because SFG rickettsiae share extensive antigenic cross-reactivity, species-specific confirmation requires PCR/sequencing (or cross-adsorption serology) (PMID: 20404224):

"The SFG rickettsioses share many clinical manifestations and extensive antigenic cross-reactivity that may hamper specific confirmation of the causative agent."

Common laboratory abnormalities: mild thrombocytopenia, lymphopenia, and elevated hepatic transaminases (≥60% of cases have altered labs; PMID: 33989945).

Suggested NCIT terms: Doxycycline (NCIT:C305); Antibiotic Therapy (NCIT:C15844); Polymerase Chain Reaction (NCIT:C17003); Immunohistochemistry (NCIT:C16681).

6. Epidemiology (F006)

R. parkeri rickettsiosis is a reportable SFG rickettsiosis primarily affecting adults, especially males aged 18–64, with tick-exposure history in >90% of cases; confirmed/probable cases have been reported in the United States, Argentina, Brazil, Uruguay, and Colombia (PMID: 33989945):

"our results show that R. parkeri rickettsiosis is more frequent in males in the age group of 18-64 years and that a history of tick exposure was frequent (>90%). Cases were described in the United States, Argentina, Brazil, Uruguay and Colombia"

In the US it is reported under the nationally notifiable aggregate category "spotted fever rickettsiosis" (species-nonspecific due to serologic cross-reactivity). US tickborne bacterial/protozoan disease reports more than doubled from 2004 to 2016 (PMID: 29723166). In Argentina, two epidemiologic scenarios coexist — severe R. rickettsii (Amblyomma cajennense complex) versus benign R. parkeri (vectors A. triste, A. tigrinum) (PMID: 30928146):

"R. parkeri produces benign and self-limited clinical manifestation"

7. Temporal course and prognosis (F007)

Onset is acute, typically 7–10 days after the tick bite. Patients develop a progressively enlarging inoculation eschar, then exanthem/maculopapular (sometimes vesiculopustular) rash, regional lymphadenopathy, fever, myalgia, and prostration (PMID: 42745336):

"All patients developed symptoms 7-10 days after the bite, including inoculation eschar with progressive enlargement, exanthema, regional lymphadenopathy, fever, myalgia, and prostration; all responded to doxycycline treatment"

The disease is self-limited and benign, and across all reported cases worldwide none have been fatal:

"So far, none of the cases have been associated with death"

This contrasts sharply with RMSF (R. rickettsii), which carries a high case-fatality rate if untreated (pediatric under-treatment concerns highlighted in PMID: 24252781).

8. Prevention (F008)

No licensed human vaccine exists for any SFG rickettsiosis; prevention is behavioral and environmental. Primary prevention includes avoiding tick habitat, using repellents (DEET, permethrin-treated clothing), performing tick checks, and prompt removal of attached ticks. Because dogs are hosts/sentinels that bring vector ticks into peridomestic settings, control programs emphasize canine ectoparasite control and public awareness (PMID: 35293560):

"the results of the present study indicate the importance of implementing programs to control canine ectoparasites and to raise awareness of the risks of infection, signs and symptoms of SF caused by R. parkeri strain Atlantic Rainforest"

Secondary prevention is early eschar recognition and prompt empiric doxycycline. Antibiotic prophylaxis after tick bite is not recommended for SFG rickettsioses (PMID: 16572105).

9. Taxonomy and zoonotic ecology (F009)

Causative agent: Rickettsia parkeri Lackman et al., 1965 (NCBI Taxonomy ID 35792), an obligate intracellular Gram-negative alphaproteobacterium of the spotted fever group. It is a tick-borne zoonosis with no human-to-human transmission. Ticks are both vector and reservoir, maintaining the bacterium transstadially and transovarially. Dogs are excellent sentinels (PMID: 42019180):

"Dogs have been recognized as good sentinels for these rickettsioses, since they are hosts to different species and stages of ticks, and they sustain a good immunological response after infection"

Natural infection is documented across diverse tick species (A. maculatum, A. ovale, A. triste, A. tigrinum, A. nodosum strain NOD, A. parvum) and in wild carnivores/small mammals across the Americas (PMID: 41133807; PMID: 41880873):

"three adults of A. nodosum contained DNA of Rickettsia parkeri Lackman et al., 1965 strain NOD"

10. Anatomical structures affected (F010)

The primary anatomical lesion is the skin at the tick-bite site — an inoculation eschar (tache noire): a central zone of dermal–epidermal necrosis with surrounding perivascular lymphohistiocytic inflammation and small-vessel (necrotizing) vasculitis, the histopathologic hallmark of SFG rickettsioses (PMID: 20404224):

"We report 3 cases of SFG rickettsiosis and discuss the epidemiology, clinical presentation, histopathologic features, and laboratory findings that support confirmed or probable diagnoses of R parkeri infection"

Regional (draining) lymph nodes are frequently enlarged, and the disseminated rash reflects widespread small-vessel endothelial infection. The cellular target is the vascular endothelial cell (CL:0000115); the bacterium replicates free in the host-cell cytoplasm (GO:0005737). Unlike RMSF, systemic organ involvement (lung, brain, kidney) is minimal or absent because disease remains largely localized and self-limited.

Suggested UBERON terms: skin of body (UBERON:0002097), dermis (UBERON:0002067), endothelium of blood vessel (UBERON:0001986), lymph node (UBERON:0000029), integumentary system (UBERON:0002416).

11. Genetic/molecular basis is bacterial, not human (F011)

R. parkeri rickettsiosis is an infectious disease with no human germline/somatic causal gene, no Mendelian inheritance, no pathogenic human variant, and no chromosomal abnormality — the genetic sections of a heritable-disease template are not applicable. Host genetics contributes only to susceptibility via innate immune pathways (e.g., type I interferon signaling; PMID: 34423779). The relevant genetics is that of the pathogen:

Gene	Product / role
ompA (sca0)	Outer membrane protein A; adhesin; diagnostic/typing target
ompB (sca5)	Outer membrane protein B; cell entry
sca2	Formin-mimic driving late actin-based motility (PMID: 20972427)
rickA	Arp2/3 activator driving early motility (PMID: 24361066)
gltA	Citrate synthase; molecular typing
sca4 (gene D)	Surface cell antigen

Phylogenetics supports multiple distinct R. parkeri strains in the New World (PMID: 29439989), and inter-tick-species sequence differences occur in cell-entry genes (PMID: 41749360):

"Differences in cellular-entry and pathogen chromosomal genes (OmpA, OmpB, and 16S) were detected within the different tick species"

12. Identifiers and synonyms (F012)

Preferred name: Rickettsia parkeri rickettsiosis (MONDO:0000234).

Identifier	Value
MONDO	MONDO:0000234
ICD-10	A77.8 "Other spotted fevers"
ICD-11	1C30.2 "Spotted fever due to other Rickettsia species" (or 1C30.Y)
MeSH	No species-specific descriptor; indexed under "Rickettsia Infections" (D012373); organism "Rickettsia parkeri"
OMIM	None (not a heritable disease)
Orphanet	No dedicated number (not a rare genetic disorder)
NCBI Taxonomy (agent)	35792 (Rickettsia parkeri)

Synonyms: R. parkeri spotted fever; Tidewater spotted fever; American boutonneuse fever; "maculatum infection/disease"; and for the South American strain, Atlantic rainforest spotted fever / mata atlântica spotted fever (PMID: 18808353; PMID: 36693294):

"Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004."

Information source: aggregated disease-level literature (case series, systematic reviews, surveillance) — not single-patient EHR resources.

13. Model systems (F013)

In vivo: Type I/II interferon-receptor-deficient mice (Ifnar1⁻/⁻, Ifnar1⁻/⁻Ifngr1⁻/⁻) are susceptible and develop eschar-associated rickettsiosis after intradermal inoculation — the first tractable mammalian model recapitulating the human eschar (PMID: 34423779). Immunocompetent wild-type mice are largely resistant (a key limitation).
In vitro: Vero cells and human microvascular endothelial cells allow direct visualization of actin-based motility and cell-to-cell spread (PMID: 24361066; PMID: 20972427); tick cell lines model the arthropod host.
Historical: Guinea pigs model SFG rickettsial fever/scrotal reaction.

14. Consolidated conclusion (F014)

Across all evidence, R. parkeri rickettsiosis is a mild, self-limited, tick-borne SFG rickettsiosis (fever ~93%, eschar ~87%, rash ~68%; PMID: 33989945), with no confirmed deaths (PMID: 42745336) and uniform doxycycline responsiveness (PMID: 16572105). The single most useful diagnostic discriminator from RMSF is the inoculation eschar, characteristic of R. parkeri and essentially absent in RMSF; the first US series framed the disease by "its clinical distinction from Rocky Mountain spotted fever" and found it "similar to but less severe than" RMSF (PMID: 18808353).

Mechanistic Model / Interpretation

Ordered causal chain (initiating exposure → clinical manifestation)

1.  Infected Amblyomma tick attaches and feeds on human skin (7–10 day incubation)
│  leads to
2.  R. parkeri inoculated into the dermis at the bite site
│  results in
3.  Bacteria adhere to and invade vascular ENDOTHELIAL cells
│  (adhesins OmpA/OmpB; cell entry) — results in
4.  Phagosomal escape → replication free in host-cell CYTOPLASM
│  leads to
5.  Two-phase ACTIN-BASED MOTILITY:
├─ EARLY: RickA activates host Arp2/3 → slow, meandering motility
└─ LATE:  Sca2 (formin-mimic) → fast, directional cell-to-cell spread
│  results in
6.  Local endothelial infection + host innate immune response
│  (type I IFN protective; bacterium antagonizes IFN via inflammasome)
│  leads to
7.  Focal NECROTIZING VASCULITIS of small dermal vessels
│  results in
8.  INOCULATION ESCHAR (tache noire) at bite site  ← hallmark lesion
│  and (branch) limited hematogenous/lymphatic spread
├─ leads to → maculopapular/vesiculopustular RASH (disseminated endothelium)
├─ leads to → regional LYMPHADENOPATHY (draining nodes)
└─ leads to → systemic FEVER, headache, myalgia; mild lab abnormalities
│  In immunocompetent hosts:
9.  Host immune control (+ doxycycline) → SELF-LIMITED RESOLUTION, no death

Upstream vs downstream: Steps 1–5 (inoculation, endothelial invasion, cytoplasmic replication, actin motility) are upstream drivers; steps 7–8 (vasculitis, eschar) are the proximate downstream lesions producing the clinical phenotype. The interferon axis (step 6) is a modulating branch that determines whether infection is contained (immunocompetent hosts, most humans) or progresses (interferon-receptor-deficient mice). Steps 3–5 are directly demonstrated in cell culture; step 6's protective role is demonstrated in mouse knockouts and inferred for humans.

Why R. parkeri is milder than RMSF (interpretation): The disease remains largely localized to the inoculation site and skin, with minimal systemic endothelial injury to lung/brain/kidney — the opposite of the widespread, high-permeability endothelial damage that makes R. rickettsii (RMSF) lethal. The eschar is therefore both the pathologic signature and a marker of contained, localized disease.

Comparison table: R. parkeri vs RMSF (R. rickettsii)

Feature	R. parkeri rickettsiosis	Rocky Mountain spotted fever
Vector	A. maculatum, A. ovale, A. triste	Dermacentor spp., A. sculptum
Inoculation eschar	Present (~87%) — hallmark	Typically absent
Rash	Maculopapular/vesiculopustular	Maculopapular → petechial
Systemic organ injury	Minimal / localized	Severe, multi-organ
Case fatality	~0% (no confirmed deaths)	High if untreated
Treatment	Doxycycline (uniform response)	Doxycycline (urgent)

Evidence Base

PMID	Title (abbrev.)	Supports
33989945	Clinical/epidemiological/lab features: systematic review	Pooled phenotype frequencies; demographics (F001, F006)
18808353	R. parkeri rickettsiosis and its clinical distinction from RMSF	Milder-than-RMSF; diagnostics; name/first description (F001, F005, F012, F014)
36693294	Inoculation eschar in Brazil	Atlantic rainforest strain/vector; eschar (F002, F012)
42661358	Gulf Coast ticks + R. parkeri, Ohio	Range expansion (F002)
42314659	Surveillance, southern Illinois	16.4% tick infection; range expansion (F002, F006)
19327117	Host-cell interactions with pathogenic Rickettsia	Endothelial tropism; rickettsial vasculitis (F003, F010)
24361066	Actin motility in distinct phases	Two-phase RickA/Sca2 motility (F003, F011, F013)
20972427	Sca2 is a bacterial formin-like mediator	Sca2 formin-mimic mechanism (F003, F011, F013)
37028467	Cryo-EM of Sca2 formin-like core	Sca2 structure (F003)
42048062	Divergent Rickettsia motility mechanisms	Species divergence in motility (F003)
34423779	IFN receptor-deficient mice susceptible	Protective type I IFN; eschar mouse model (F004, F013)
32123346	Inflammasome antagonism of type I IFN	Immune cross-talk enhances pathogenesis (F004)
16572105	Diagnosis/management of tickborne rickettsial diseases	Doxycycline first-line; no prophylaxis (F005, F008)
20404224	Expanding spectrum of eschar-associated rickettsioses	Histopathology; serologic cross-reactivity (F005, F010)
30928146	Spotted fever in Argentina	Benign course; Argentine vectors (F006, F007)
42745336	First outbreak of Atlantic Rainforest SF in NE Brazil	Incubation, symptom sequence; no deaths (F007, F014)
35293560	New focus of SF by R. parkeri in Brazil	Canine ectoparasite control / prevention (F008)
42019180	SFG rickettsiae in dogs of the Americas: meta-analysis	Dogs as sentinels; zoonotic ecology (F009)
41133807	Rickettsia in horses/ticks, Pernambuco	Multi-tick natural infection; species authority (F009)
41880873	Rickettsia in Cerrado carnivores	Wild reservoir ecology (F009)
29439989	Multiple strains of R. parkeri in the New World	Pathogen strain diversity (F011)
41749360	R. parkeri diversity from three tick species	Cell-entry gene variation; vector competence (F002, F011)
29723166	Vital Signs: vectorborne disease trends 2004–2016	Rising tickborne disease burden (F006)
23440128	R. parkeri in A. triste, Argentina	Molecular typing targets; Argentine vector (F011)
24252781	Provider treatment practices, RMSF	Context: RMSF lethality/doxycycline under-use

Evidence source types: Human clinical (case series, systematic reviews: 33989945, 18808353, 42745336, 30928146, 20404224); epidemiologic/surveillance (42314659, 42661358, 29723166); veterinary/ecologic (42019180, 41880873, 41133807, 32267390); in vitro / cell biology (24361066, 20972427, 37028467, 42048062); model organism (34423779, 32123346); phylogenetic/computational (29439989, 41749360, 23440128).

Limitations and Knowledge Gaps

Under-recognition and surveillance dilution. In the US, R. parkeri cases are folded into the aggregate "spotted fever rickettsiosis" notifiable category because SFG serology cross-reacts; true incidence and prevalence (cases per 100,000) are therefore not precisely quantified. Species-level burden is likely underestimated.
Small evidence base. The definitive clinical picture rests on 77 pooled cases (PMID: 33989945) plus scattered series. No large prospective cohorts or randomized treatment trials exist.
No confirmed deaths, but rare severe cases possible. The "0% fatality" statement reflects reported cases; immunocompromised or atypical presentations may be under-captured.
Model limitations. The tractable animal model requires interferon-receptor knockout mice; immunocompetent mice resist infection, so the model does not fully reproduce the mild human course or long-term immunity.
Quality-of-life / long-term outcome data are absent. Because disease is self-limited, no EQ-5D/SF-36/PROMIS data or disability outcomes have been reported.
Human genetic susceptibility is essentially unstudied. Beyond the interferon axis inferred from mouse work, no human host-genetic risk/protective factors, GWAS loci, or pharmacogenomic data exist for this disease.
Strain–virulence correlations incomplete. Whether sequence differences in ompA/ompB across strains/tick species translate into clinical severity differences is not established.

Proposed Follow-up Experiments / Actions

Species-specific surveillance: Advocate for molecular (PCR/sequencing) confirmation in reportable SFG cases to disaggregate R. parkeri from other SFG agents and generate true incidence/prevalence estimates by region.
Prospective clinical registry: Establish a multi-country (US + South America) registry capturing incubation, symptom frequencies, lab abnormalities, treatment response, and any severe/atypical outcomes to refine natural-history and prognosis data.
Strain-virulence genomics: Comparative genomics/transcriptomics of R. parkeri sensu stricto vs Atlantic rainforest vs NOD strains, correlating ompA/ompB/sca2/rickA variation with in vitro endothelial cytopathology and mouse eschar severity.
Host immunity mechanism: Dissect the type I interferon ↔ inflammasome axis (building on PMID: 34423779, PMID: 32123346) to explain why R. parkeri is contained (eschar-limited) whereas R. rickettsii disseminates.
Vector-range monitoring: Continue active tick surveillance in newly colonized northern areas (Ohio, Illinois) to forecast human risk as A. maculatum expands (PMID: 42661358, PMID: 42314659).
One-Health prevention trials: Evaluate canine ectoparasite-control programs as a community-level intervention to reduce peridomestic vector burden (PMID: 35293560).
Diagnostic assay development: Develop rapid, field-deployable species-specific molecular assays for eschar-crust testing to overcome serologic cross-reactivity (PMID: 20404224).

Ontology Annotation Summary

Category	Terms
Disease	MONDO:0000234 (Rickettsia parkeri rickettsiosis)
Phenotypes (HPO)	HP:0001945 (Fever), HP:0200042 (Skin ulcer/eschar), HP:0002716 (Lymphadenopathy), HP:0002315 (Headache), HP:0003326 (Myalgia), HP:0001873 (Thrombocytopenia), HP:0001888 (Lymphopenia), HP:0002910 (Elevated hepatic transaminases)
Cell types (CL)	CL:0000115 (endothelial cell)
Anatomy (UBERON)	UBERON:0002097 (skin), UBERON:0002067 (dermis), UBERON:0001986 (endothelium of blood vessel), UBERON:0000029 (lymph node)
Biological process (GO)	GO:0030048 (actin filament-based movement), GO:0034314 (Arp2/3-mediated actin nucleation), GO:0045010 (actin nucleation), GO:0060337 (type I interferon signaling), GO:0061702 (inflammasome complex)
Cellular component (GO)	GO:0005737 / GO:0030430 (cytoplasm / host cell cytoplasm)
Chemical (CHEBI)	CHEBI:50845 (doxycycline)
Treatment (NCIT)	NCIT:C305 (Doxycycline), NCIT:C15844 (Antibiotic Therapy)
Pathogen (NCBI Taxon)	35792 (Rickettsia parkeri)

Report compiled from 14 confirmed findings and 34 reviewed papers across a 5-iteration autonomous investigation. All quoted material is verbatim from the cited PubMed abstracts.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.3.0rc3.

Outcome	Count
References checked	25
Resolved	25
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	2
Quoted claims found in source	2
Quoted claims not found in source	0
References weighed for topical relevance	25
On topic	21
Off topic	0

All extracted references resolved successfully.

Term Validation

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

Outcome	Count
Terms checked	29
Resolved	29
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	0
Terms whose name was checked	3
Terms named correctly	2
Terms named as a different term	1

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:0000234 (4 mentions) - the report calls it "MONDO", "Rickettsia parkeri rickettsiosis"; MONDO calls it Rickettsia parkeri spotted fever

Terms named inconsistently

The report gives these identifiers more than one name of its own:

MONDO:0000234 - called "MONDO", "Rickettsia parkeri rickettsiosis"

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Pathophysiology

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Phenotypes

Medical Actions

Environmental Factors

Diagnosis

Progression

Epidemiology

Infectious Agent

Transmission

Clinical Burden

Animal Models

Source YAML

References & Deep Research

Deep Research

Key Findings

1. Clinical profile: an eschar-associated febrile illness milder than RMSF (F001)

2. Vector biology and strain geography (F002)

3. Core pathophysiology: endothelial infection and two-phase actin-based motility (F003)

4. Immune mechanism: type I interferon is protective (F004)

5. Diagnosis and treatment (F005)

6. Epidemiology (F006)

7. Temporal course and prognosis (F007)

8. Prevention (F008)

9. Taxonomy and zoonotic ecology (F009)

10. Anatomical structures affected (F010)

11. Genetic/molecular basis is bacterial, not human (F011)

12. Identifiers and synonyms (F012)

13. Model systems (F013)

14. Consolidated conclusion (F014)

Mechanistic Model / Interpretation

Ordered causal chain (initiating exposure → clinical manifestation)

Comparison table: R. parkeri vs RMSF (R. rickettsii)

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Ontology Annotation Summary

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Terms named inconsistently