Geographic Distribution

American dog tick (Dermacentor variabilis) is the most commonly identified species responsible for transmitting Rickettsia rickettsii, which causes Rocky Mountain spotted fever in humans. The American dog tick can also transmit tularemia. This tick is widely distributed east of the Rocky Mountains and also occurs in limited areas on the Pacific Coast. D. variabilis larvae and nymphs feed on small rodents. Dogs and medium-sized mammals are the preferred hosts of adult D. variabilis, although it feeds readily on other large mammals, including humans.

The blacklegged tick (Ixodes scapularis), commonly known as a "deer tick", can transmit the organisms responsible for anaplasmosis, babesiosis, and Lyme disease. This tick is widely distributed in the northeastern and upper midwestern United States. I. scapularis larvae and nymphs feed on small mammals and birds, while adults feed on larger mammals and will bite humans on occasion. It is important to note that the pathogen that causes Lyme disease is maintained by wild rodent and other small mammal reservoirs, and is not transmitted everywhere that the blacklegged tick lives. In some regions, particularly in the southern U.S., the tick has very different feeding habits that make it an unlikely vector in the spread of human disease.

The brown dog tick (Rhipicephalus sanguineus) has recently been identified as a reservoir of R. rickettsii, causing Rocky Mountain spotted fever, in the southwestern U.S. and along the U.S-Mexico border. Brown dog ticks are found throughout the U.S. and the world. Dogs are the primary host for the brown dog tick for each of its life stages, although the tick may also bite humans or other mammals.

The Gulf Coast tick resides in coastal areas of the United States along the Atlantic coast and the Gulf of Mexico. The Gulf Coast tick can transmit Rickettsia parkeri rickettsiosis, a form of spotted fever. A. maculatum larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other wildlife. Adult ticks have been associated with transmission of R. parkeri to humans.

The lone star tick (Amblyomma americanum) transmits Ehrlichia chaffeensis and Ehrlichia ewingii, causing human ehrlichiosis, tularemia, and STARI. The lone star tick is primarily found in the southeastern and eastern United States. White-tailed deer are a major host of lone star ticks and appear to represent one natural reservoir for E. chaffeensis. A. americanum larvae and nymphs feed on birds and deer. Both nymphal and adult ticks may be associated with the transmission of pathogens to humans.

Rocky Mountain wood tick (Dermacentor andersoni) can transmit Rocky Mountain spotted fever and tularemia to humans. This tick is found in the Rocky Mountain states. Adult ticks feed primarily on large mammals. Larvae and nymphs feed on small rodents. Adult ticks are primarily associated with pathogen transmission to humans.

The western blacklegged tick (Ixodes pacificus) can transmit the organisms responsible for causing anaplasmosis and Lyme disease in humans. Wild rodents and other mammals are likely reservoirs of these pathogens. This tick is distributed along the Pacific coast of the United States. Larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other mammals. Adult ticks are primarily associated with pathogen transmission to humans.