Rocky mountain spotted fever, which is caused by Rickettsia rickettsii, is a life-threatening, tick-borne disease that occurs throughout much of the United States. Case fatality rates can be as high as 20 percent in untreated patients.1,2 The principal recognized vectors of R. rickettsii are Dermacentor variabilis (the American dog tick) (Figure 1A) in the eastern and central United States and D. andersoni (the Rocky Mountain wood tick) (Figure 1B) in the western United States. Both types of tick feed on small mammals, which may harbor R. rickettsii. D. variabilis, the most common tick associated with Rocky Mountain spotted fever, also commonly feeds on dogs.3 Another common tick throughout the world that feeds on dogs, Rhipicephalus sanguineus (the brown dog tick) (Figure 1C), has not previously been reported to be a natural vector for Rocky Mountain spotted fever in the United States.
Rocky Mountain spotted fever is rarely reported in Arizona, and the expected Dermacentor species vectors are not commonly found in the state.4 From 1981 through 2001, only three cases of Rocky Mountain spotted fever were reported for the entire state.1,2 However, from 2002 through 2004, Rocky Mountain spotted fever was identified in 16 patients from rural eastern Arizona. In this report, we describe that outbreak and summarize the clinical, epidemiologic, and ecologic findings that implicate R. sanguineus as a newly recognized vector for R. rickettsii in the region.
From the National Center for Infectious Diseases, Division of Viral and Rickettsial Diseases and the Epidemic Intelligence Service, Office of Workforce and Career Development, the Centers for Disease Control and Prevention, Atlanta; the Indian Health Service, Whiteriver Service Unit, Whiteriver, Ariz.; and the Indian Health Service, National Epidemiology Program, Albuquerque, N.M.
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