Diseases Transmitted by Ticks

In the United States, some ticks carry pathogens that can cause human disease, including:

  • Anaplasmosis is transmitted to humans by tick bites primarily from the blacklegged tick (Ixodes scapularis) in the northeastern and upper midwestern U.S. and the western blacklegged tick (Ixodes pacificus) along the Pacific coast.
  • Babesiosis is caused by microscopic parasites that infect red blood cells. Most human cases of babesiosis in the U.S. are caused by Babesia microti. Babesia microti is transmitted by the blacklegged tick (Ixodes scapularis) and is found primarily in the northeast and upper midwest.
  • Borrelia mayonii infection has recently been described as a cause of illness in the upper midwestern United States. It has been found in blacklegged ticks (Ixodes scapularis) in Minnesota and Wisconsin. Borrelia mayonii is a new species and is the only species besides B. burgdorferi known to cause Lyme disease in North America.
  • Borrelia miyamotoi infection has recently been described as a cause of illness in the U.S. It is transmitted by the blacklegged tick (Ixodes scapularis) and has a range similar to that of Lyme disease.
  • Bourbon virus infection has been identified in a limited number patients in the Midwest and southern United States. At this time, we do not know if the virus might be found in other areas of the United States.
  • Colorado tick fever is caused by a virus transmitted by the Rocky Mountain wood tick (Dermacentor andersoni). It occurs in the the Rocky Mountain states at elevations of 4,000 to 10,500 feet.
  • Ehrlichiosis is transmitted to humans by the lone star tick (Ambylomma americanum), found primarily in the southcentral and eastern U.S.
  • Heartland virus cases have been identified in the Midwestern and southern United States. Studies suggest that Lone Star ticks can transmit the virus. It is unknown if the virus may be found in other areas of the U.S.
  • Lyme disease is transmitted by the blacklegged tick (Ixodes scapularis) in the northeastern U.S. and upper midwestern U.S. and the western blacklegged tick (Ixodes pacificus) along the Pacific coast.
  • Powassan disease is transmitted by the blacklegged tick (Ixodes scapularis) and the groundhog tick (Ixodes cookei). Cases have been reported primarily from northeastern states and the Great Lakes region.
  • Rickettsia parkeri rickettsiosis is transmitted to humans by the Gulf Coast tick (Amblyomma maculatum).
  • Rocky Mountain spotted fever (RMSF) is transmitted by the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and the brown dog tick (Rhipicephalus sangunineus) in the U.S. The brown dog tick and other tick species are associated with RMSF in Central and South America.
  • STARI (Southern tick-associated rash illness) is transmitted via bites from the lone star tick (Ambylomma americanum), found in the southeastern and eastern U.S.
  • Tickborne relapsing fever (TBRF) is transmitted to humans through the bite of infected soft ticks. TBRF has been reported in 15 states: Arizona, California, Colorado, Idaho, Kansas, Montana, Nevada, New Mexico, Ohio, Oklahoma, Oregon, Texas, Utah, Washington, and Wyoming and is associated with sleeping in rustic cabins and vacation homes.
  • Tularemia is transmitted to humans by the dog tick (Dermacentor variabilis), the wood tick (Dermacentor andersoni), and the lone star tick (Amblyomma americanum). Tularemia occurs throughout the U.S.
  • 364D rickettsiosis (Rickettsia phillipi, proposed) is transmitted to humans by the Pacific Coast tick (Dermacentor occidentalis ticks). This is a new disease that has been found in California.

This list shows the most common tickborne diseases outside the United States, but does not list every disease.

  • Crimean-Congo hemorrhagic fever is found in Eastern Europe, particularly in the former Soviet Union; in northwestern China; central Asia; southern Europe; Africa; the Middle East; and the Indian subcontinent.
  • Imported tickborne spotted fevers (rickettsial infections) have caused infection in returning travelers. In the U.S., the most frequently diagnosed rickettsial infection associated with international travel is caused by Rickettsia africae (the agent of African spotted fever).
  • Kyasanur forest disease is found in southern India and is typically associated with exposure to ticks while harvesting forest products. Additionally, a similar virus has been described in Saudi Arabia (Alkhurma hemorrhagic fever virus).
  • Lyme disease can be contracted in temperate forested regions throughout Europe and northern Asia, although it is more common in eastern and central Europe than western Europe. Lyme disease outside the United States is often caused by different genospecies of Borrelia burgdorferi sensu lato and may have somewhat different symptoms. Antibodies to Borrelia burgdorferi sensu lato species that cause infection outside the United States may not be reliably detected by all tests used for Lyme disease in the United States. Providers who suspect internationally-acquired Lyme disease should use diagnostic tests that have been validated for these species.
  • Omsk Hemorrhagic Fever (OHF) occurs in the western Siberia regions of Omsk, Novosibirsk, Kurgan, and Tyumen. It may be also be acquired by direct contact with infected muskrats.
  • Tickborne encephalitis (TBE) occurs in some forested areas in Europe and Asia, from eastern France to northern Japan and from northern Russia to Albania. TBE is caused by TBE virus, a flavivirus that is closely related to Powassan virus. TBE virus has three subtypes: European, Siberian, and Far Eastern. TBE virus is primarily transmitted to humans by infected Ixodes species ticks. It can also be acquired by ingesting unpasteurized dairy products (such as milk and cheese) from infected goats, sheep, or cows.

Note: Anaplasmosis, babesiosis, ehrlichiosis, tularemia, tickborne relapsing fever, Rocky Mountain spotted fever, and Powassan disease can also be acquired internationally.

See also: