Potentially Deadly Tick Species in the United States
Medically significant species capable of transmitting fatal diseases to humans
| Image | Tick Species | Primary Region | Potentially Fatal Disease(s) | Case Fatality Rate (if untreated) |
|---|---|---|---|---|
 |
American Dog Tick Dermacentor variabilis |
East of Rockies; Pacific Coast | Rocky Mountain Spotted Fever, Tularemia, Tick Paralysis | RMSF: up to 20–25% untreated; ~3–5% with delayed treatment |
 |
Rocky Mountain Wood Tick Dermacentor andersoni |
Western US (above 4,000 ft) | Rocky Mountain Spotted Fever, Colorado Tick Fever, Tick Paralysis | RMSF: up to 20–25% untreated; Tick paralysis can cause fatal respiratory failure |
 |
Brown Dog Tick Rhipicephalus sanguineus |
Nationwide (esp. Southwest US) | Rocky Mountain Spotted Fever, Q Fever | RMSF: up to 20–25% untreated; especially virulent strain in Southwest |
 |
Blacklegged (Deer) Tick Ixodes scapularis |
Eastern US | Lyme disease, Powassan virus encephalitis, Babesiosis, Anaplasmosis | Powassan: ~10–15% fatality; Babesiosis: up to 20% in high-risk patients |
 |
Western Blacklegged Tick Ixodes pacificus |
Far Western US (esp. California) | Lyme disease, Powassan virus, Babesiosis, Anaplasmosis | Powassan: ~10–15% fatality; Babesiosis: up to 20% in high-risk patients |
 |
Lone Star Tick Amblyomma americanum |
Eastern/Southern US | Ehrlichiosis (HME), Heartland virus, Bourbon virus, RMSF, Tularemia | Ehrlichiosis: ~2–3% fatality; Heartland/Bourbon virus: rare but fatal cases documented |
 |
Pacific Coast Tick Dermacentor occidentalis |
Southwest US / California to Oregon | Rocky Mountain Spotted Fever, Colorado Tick Fever, Tularemia | RMSF: up to 20–25% untreated |
 |
Soft Ticks Ornithodoros spp. |
Western US (coniferous forests, caves) | Tick-borne Relapsing Fever (TBRF) | Rare fatalities; severe in elderly, immunocompromised, and infants |
Sources: CDC, NIH/PMC (Eisen 2022), LymeDisease.org — Most tick-borne fatalities result from delayed diagnosis, not the bite itself. Prompt treatment with doxycycline is critical for rickettsial diseases.
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