Murine typhus is an acute illness characterized by symptoms similar to those of epidemic typhus but milder in character. Unlike its epidemic relative, it is a natural infection of the rat and transmitted sporadically to humans by the rat flea, Xenopsylla cheopis. Its relation to the rat is reflected in the name murine typhus. The etiologic agent is Rickettsia typhi.

Clinical Manifestations

Symptoms and the course of illness in murine typhus are similar to those in epidemic, louse-borne typhus. For this reason, distinguishing between the two diseases has been difficult. The flea-borne illness, however, is almost never fatal, with about a 2 percent mortality in persons over age 50.

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 prowazekii. In guinea pigs, R. typhi causes a characteristic reaction in scrotal cells useful for distinguishing between murine and epidemic typhus.