Ticks are small arachnids that pose serious health risks by transmitting pathogens, including viruses, bacteria, and parasites, to humans. Among all tick species worldwide, only a small number carry harmful pathogens. Different species are linked to distinct diseases, making accurate identification essential for disease prevention. While adult ticks are easier to recognize, nymphal and larval ticks are much smaller and harder to distinguish.
Tick-Borne Diseases in the United States
Some ticks in the U.S. carry pathogens that cause serious human illnesses. Below are some of the most common tick-borne diseases and their transmission patterns:
Anaplasmosis – Spread by the blacklegged tick (Ixodes scapularis) in the Northeast and Midwest and the western blacklegged tick (Ixodes pacificus) along the Pacific Coast.
Babesiosis – A red blood cell infection caused by Babesia microti, mainly found in the Northeast and Midwest. Transmitted by the blacklegged tick.
Borrelia mayonii Infection – A newly identified Lyme disease-causing bacterium in the Midwest, found in Ixodes scapularis.
Borrelia miyamotoi Infection – Another Lyme-related illness carried by the blacklegged tick.
Bourbon Virus – A rare viral infection identified in the Midwest and Southern U.S. Transmission methods remain unclear.
Colorado Tick Fever – A viral illness spread by the Rocky Mountain wood tick (Dermacentor andersoni) in high-altitude regions of the Rocky Mountains.
Ehrlichiosis – Carried by the lone star tick (Amblyomma americanum), found primarily in the South-Central and Eastern U.S.
Heartland Virus – Identified in the Midwest and South, likely transmitted by lone star ticks.
Lyme Disease – The most well-known tick-borne illness in the U.S., caused by Borrelia burgdorferi and transmitted by Ixodes scapularis in the Northeast and Midwest and Ixodes pacificus along the Pacific Coast.
Powassan Virus – A rare but serious viral infection spread by the blacklegged tick and groundhog tick (Ixodes cookei), mostly found in the Northeast and Great Lakes region.
Rickettsia parkeri Rickettsiosis – A spotted fever illness transmitted by the Gulf Coast tick (Amblyomma maculatum).
Rocky Mountain Spotted Fever (RMSF) – A severe bacterial infection spread by the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick, and brown dog tick (Rhipicephalus sanguineus).
STARI (Southern Tick-Associated Rash Illness) – Transmitted by lone star ticks, found mainly in the Southeast and Eastern U.S.
Tickborne Relapsing Fever (TBRF) – Caused by Borrelia bacteria, transmitted by soft ticks in Western states and associated with rustic cabins and vacation homes.
Tularemia – A bacterial disease spread by the dog tick, wood tick, and lone star tick.
364D Rickettsiosis – A recently discovered bacterial illness in California, transmitted by the Pacific Coast tick (Dermacentor occidentalis).
Common Ticks and Their Distribution
American Dog Tick
Location: Common east of the Rocky Mountains, with some presence on the Pacific Coast.
Bite Risks: Nymphs and adult females most commonly bite humans, but all stages can transmit diseases.
Final Thoughts
Ticks present a significant health risk, particularly in areas where certain species are more prevalent. Understanding which ticks carry diseases, their geographic distribution, and the illnesses they cause is essential for prevention. With tick populations expanding, proper identification and awareness of their risks can help reduce the likelihood of infection.
Mary Watson
