| Disease | Organism | Geographic distribution and vector | Typical clinical findingsa |
|---|---|---|---|
| Rocky Mountain spotted fever (RMSF) | Rickettsia rickettsii | Eastern United States: Dermacentor variabilis (dog tick) Mountain West: Dermacentor andersoni (wood tick) Southwestern deserts: Rhipicephalus sanguineus (brown dog tick) | Fever, headache, petechial rash, hyponatremia, thrombocytopenia |
| Rickettsia parkeri infection | Rickettsia parkeri | Southeastern United States: Amblyomma maculatum (Gulf Coast tick) | Similar to RMSF, but with eschar at inoculation site; rash may be vesicular or pustular; gastrointestinal symptoms less prominent |
| Human monocytotropic ehrlichiosis (HME) | Ehrlichia chaffeensis | Southeastern and southcentral states: Amblyomma americanum (Lone Star tick) | Similar to RMSF, but rash less common; leukopenia, thrombocytopenia, elevated transaminases |
| Human granulocytotropic anaplasmosis (HGA)b | Anaplasma phagocytophilum | Northeast and upper Midwest: Ixodes scapularis (blacklegged tick) Pacific coast: Ixodes pacificus | Similar to HME, but rash is rarely present |
| Ehrlichia ewingii infection | Ehrlichia ewingii | Southeastern and southcentral states: A. americanum | Same as HGA |
| Lyme disease | Borrelia burgdorferi | Northeast and upper Midwest: I. scapularis Pacific coast: I. pacificus | First stage: fever, erythema migrans Second stage: multiple skin lesions, conjunctivitis, arthralgias, myalgias, headache, cranial nerve palsies Third stage: arthritis; encephalopathy, dementia, peripheral neuropathy |
| Southern tick-associated rash illness | Borrelia lonestari | Southeastern and southcentral states: A. americanum | Rash similar to erythema migrans |
| Endemic relapsing fever | Borrelia hermsii B. turicatae B. parkeri | Western mountains and deserts: Ornithodoros species | Fever, chills, relapsing course |
| Tularemia | Francisella tularensis | Eastern United States: D. variabilis Mountain West: D. andersoni Southeastern and southcentral states: A. americanum | Fever, cutaneous eschar, lymphadenopathy, pulse–temperature dissociation |
| Babesiosis | Babesia microti | Northeast, Midwest, and West Coast: I. scapularis, other Ixodes species | Fever, malaise, headache, hepatosplenomegaly, thrombocytopenia, hemolytic anemia |
| Colorado tick fever | Coltivirus | Mountain West: D. andersoni | Fever, headache, leukopenia, thrombocytopenia; biphasic course |
| Powassan encephalitis | Powassan virus | Northeastern, north-central United States: Ixodes species, D. andersoni | Headache, seizures, altered sensorium, focal neurologic signs, meningismus |
| Tick paralysisc | Neurotoxin |
