Epidemics usually occur in cold months in poor highland areas, such as the Andes, Himalayas, Mexico, Central America, and Africa. Lice live in clothing, attach to the human host several times daily to take a blood meal, and become infected with R prowazekii if the host has rickettsiae circulating in the blood.

Where is Rickettsia most common?

In the United States, the tick species that is most frequently associated with transmission of R. rickettsii is the American dog tick, Dermacentor variabilis ( Figure 2). This tick is found primarily in the eastern, central, and Pacific coastal United States ( Figure 3).

Where do Rickettsia species live within the host cell?

Rickettsia species are Gram-negative, obligate intracellular bacteria known to derive their nutrition primarily from the cytoplasm of the host cell.