Arizona: Rocky Mountain Spotted Fever 2003-2005

2003-2005 Highlights, Vector-Borne and Zoonotic Disease Newsletter, Arizona Department of Health Services

Rocky Mountain Spotted Fever (RMSF) has emerged as a major concern in portions of Arizona. Prior to 2004, only eight cases of RMSF had been recorded in the state. In 2004 alone, 15 cases were reported. Another 13 were added in 2005. All of the 2004-2005 cases occurred in mountainous east-central Arizona and appear to be associated with the brown dog tick, Rhipicephalus sanguineus, a species not previously known to be a vector in the U.S. It is thought that the brown dog tick, while not an efficient vector, can transmit RMSF under certain conditions, namely when the number of ticks in a community is large and dogs are allowed to roam freely. Therefore, controlling ticks on dogs and around the home as well as enforcement of animal control regulations are essential steps in preventing RMSF. A very unfortunate aspect of the current outbreak is that it has disproportionately affected children. From 2003-2005, five individuals have died from RMSF infections. RMSF, caused by Rickettsia rickettsii bacteria, is an acute febrile illness typically marked by the sudden onset of moderate to high fever with a rash forming a few days later on the extremities and spreading to the palms and soles and then the torso. Severe headache and muscle aches are also common symptoms. In some cases, infection with R. rickettsii does not produce classic symptoms. Lack of appearance of rash and/or other typical symptoms can delay diagnosis and treatment. A sweeping multi-agency RMSF response effort was undertaken in 2005 and more work is planned for 2006. Because of this recent activity, RMSF should be included in the differential diagnosis for Arizona care providers seeing patients with unexplained rash and fever illnesses. Ticks removed from patients may be submitted to ADHS-Vector for identification.

Rocky Mountain Spotted Fever from an Unexpected Tick Vector in Arizona

Rocky Mountain Spotted Fever from an Unexpected Tick Vector in Arizona, The New England Journal of Medicine

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.