Etiology and Epidemiology R. prowazekii is prevalent worldwide and transmitted to humans in feces of the human body louse Pediculus humanus when a puncture wound is contaminated by scratching. Dried louse feces may also transfer the microbe to the mucous membranes of the eyes or mouth. Humans are the natural reservoir of infection. After an incubation period of 7 to 14 days, fever, headache, and prostration suddenly occur. Headache is generalized and intense.
Splenomegaly occurs in some cases.
For diagnosis and treatment, see Differential Diagnosis and Treatment of Rickettsial Diseases, above. Affected patients either had acquired epidemic typhus earlier or lived in an endemic area. Apparently when host defenses falter, viable organisms retained in the body are activated, causing recurrent typhus. Lice that feed on patients may acquire infection and transmit the agent. Also, R. prowazekii may be isolated from the blood by animal inoculation.