Etiology and Epidemiology

Murine typhus is found worldwide and is infectious for persons of all ages (see previous chapter, Map VIII.151.1). Those living or working in areas where rats are abundant are most susceptible. Like epidemic typhus, murine typhus is transmitted mechanically, through rubbing infected feces of the flea Xenopsylla cheopis into a skin abrasion, through the eye, or through mucous membranes of the respiratory tract. In the years following World War II, active campaigns against rats and their fleas with DDT and rodenticides sharply reduced the incidence of murine typhus in the United States.

The causative agent of epidemic typhus is known as R. typhi, although some investigators prefer to call it Rickettsia mooseri in honor of Herman Mooser, a Swiss pathologist who, working in Mexico, differentiated between this organism and Rickettsia prowa-zekii. In guinea pigs, R. typhi causes a characteristic reaction in scrotal cells useful for distinguishing between murine and epidemic typhus. First noticed in 1917 by U.S. Public Health Service investigator Mather H. Neill and confirmed nearly two decades later by Mooser, the reaction became known as the Neill-Mooser phenomenon.

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