infectious diseases
Rocky Mountain Spotted Fever (RMSF)
Epidemiology of RMSF
RMSF is limited to the Western Hemisphere. Initially recognized in the Rocky Mountain states, it occurs in practically all of the United States and throughout Central and South America. In humans, infection occurs mainly from March to September, when adult ticks are active and people are most likely to be in tick-infested areas. In southern states, sporadic cases occur throughout the year. The incidence is highest in children<15 years and in people who frequent tick-infested areas for work or recreation. (See alsoCenters for Disease Control and Prevention: RMSF–epidemiology and statistics.) Hard-shelled ticks (family Ixodidae) harborR. rickettsii, and infected females transmit the agent to their progeny. These ticks are the natural reservoirs.Dermacentor andersoni(wood tick) is the principal vector in the western United States.D. variabilis(dog tick) is the vector in the eastern and southern United States. RMSF is probably not transmitted directly from person to person. 