Rocky Mountain Spotted Fever from an Unexpected Tick Vector in Arizona
Linda J. Demma, Ph.D., Marc S. Traeger, M.D., William L. Nicholson, Ph.D., Christopher D. Paddock, M.D., Dianna M. Blau, D.V.M., Ph.D., Marina E. Eremeeva, M.D., Ph.D., Gregory A. Dasch, Ph.D., Michael L. Levin, Ph.D., Joseph Singleton, Jr., B.S., Sherif R. Zaki, M.D., Ph.D., James E. Cheek, M.D., David L. Swerdlow, M.D., and Jennifer H. McQuiston, D.V.M.
Background Rocky Mountain spotted fever is a life-threatening,tick-borne disease caused by Rickettsia rickettsii. This diseaseis rarely reported in Arizona, and the principal vectors, Dermacentorspecies ticks, are uncommon in the state. From 2002 through2004, a focus of Rocky Mountain spotted fever was investigatedin rural eastern Arizona.
Methods We obtained blood and tissue specimens from patientswith suspected Rocky Mountain spotted fever and ticks from patients'homesites. Serologic, molecular, immunohistochemical, and cultureassays were performed to identify the causative agent. On thebasis of specific laboratory criteria, patients were classifiedas having confirmed or probable Rocky Mountain spotted feverinfection.
Results A total of 16 patients with Rocky Mountain spotted feverinfection (11 with confirmed and 5 with probable infection)were identified. Of these patients, 13 (81 percent) were children12 years of age or younger, 15 (94 percent) were hospitalized,and 2 (12 percent) died. Dense populations of Rhipicephalussanguineus ticks were found on dogs and in the yards of patients'homesites. All patients with confirmed Rocky Mountain spottedfever had contact with tick-infested dogs, and four had a reportedhistory of tick bite preceding the illness. R. rickettsii DNAwas detected in nonengorged R. sanguineus ticks collected atone home, and R. rickettsii isolates were cultured from theseticks.
Conclusions This investigation documents the presence of RockyMountain spotted fever in eastern Arizona, with common browndog ticks (R. sanguineus) implicated as a vector of R. rickettsii.The broad distribution of this common tick raises concern aboutits potential to transmit R. rickettsii in other settings.
Source Information
From the National Center for Infectious Diseases, Division of Viral and Rickettsial Diseases (L.J.D., W.L.N., C.D.P., D.M.B., M.E.E., G.A.D., M.L.L., J.S., S.R.Z., D.L.S., J.H.M.) and the Epidemic Intelligence Service, Office of Workforce and Career Development (L.J.D.), the Centers for Disease Control and Prevention, Atlanta; the Indian Health Service, Whiteriver Service Unit, Whiteriver, Ariz. (M.S.T.); and the Indian Health Service, National Epidemiology Program, Albuquerque, N.M. (J.E.C.).
Address reprint requests to Dr. Demma at the Centers for Disease Control and Prevention, 1600 Clifton Rd., MS D63, Atlanta, GA 30333, or at ldemma{at}cdc.gov.
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