*The New England Journal of Medicine*

Volume 353:587-594           August 11, 2005           Number 6
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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.

 .ABSTRACT

Background Rocky Mountain spotted fever is a life-threatening,
tick-borne disease caused by Rickettsia rickettsii. This disease is
rarely reported in Arizona, and the principal vectors, Dermacentor
species ticks, are uncommon in the state. From 2002 through 2004, a
focus of Rocky Mountain spotted fever was investigated in rural eastern

Arizona.

Methods We obtained {*filter*} and tissue specimens from patients with
suspected Rocky Mountain spotted fever and ticks from patients'
homesites. Serologic, molecular, immunohistochemical, and culture
assays
were performed to identify the causative agent. On the basis of
specific
laboratory criteria, patients were classified as having confirmed or
probable Rocky Mountain spotted fever infection.

Results A total of 16 patients with Rocky Mountain spotted fever
infection (11 with confirmed and 5 with probable infection) were
identified. Of these patients, 13 (81 percent) were children 12 years
of
age or younger, 15 (94 percent) were hospitalized, and 2 (12 percent)
died. Dense populations of Rhipicephalus sanguineus ticks were found on

dogs and in the yards of patients' homesites. All patients with
confirmed Rocky Mountain spotted fever had contact with tick-infested
dogs, and four had a reported history of tick bite preceding the
illness. R. rickettsii DNA was detected in nonengorged R. sanguineus
ticks collected at one home, and R. rickettsii isolates were cultured
from these ticks.

Conclusions This investigation documents the presence of Rocky Mountain

spotted fever in eastern Arizona, with common brown dog ticks (R.
sanguineus) implicated as a vector of R. rickettsii. The broad
distribution of this common tick raises concern about its 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