152 Typhus, Murine
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-bome 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 asR. 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.
History and Geography
Although murine typhus was identified only during the twentieth century, it may be an even older disease than classic, epidemic typhus. Neither of the two hosts of R. typhi, the rat and the rat flea, suffer ill effects from their infection with the organism, whereas R. prowazekii inevitably kills its vector louse and causes a serious illness in its human host.
Sporadic cases of typhuslike fevers in areas free from lice were reported early in the twentieth century in the United States, Malaya, and Australia. Often these infections were designated by local names, such as “urban” or “shop” typhus. It was not until 1926, however, that the distinctiveness of this disease was recognized. During an epidemiological investigation of such cases in the southeastern United States, U.S. Public Health Service investigator Kenneth F. Maxcy described an endemic form of typhus fever and postulated that some ectoparasite of the rat might be its vector. By 1931, infected fleas had been found in nature, confirming Maxey’s hypothesis. Although the name “endemic typhus” was used for some time, it was shortly observed that the disease could occur in epidemics as well as sporadically. In 1932 Mooser proposed that the disease be called “murine typhus” instead to indicate its relationship to rats.
Although broad-spectrum antibiotics provide effective treatment against this disease, its mild course and low fatality rate make these measures almost unnecessary. By the time the disease is diagnosed, the patient is usually in convalescence.
Victoria A. Harden
Bibliography
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Dyer, R. E., et al. 1932. Endemic typhus fever of the United States: History, epidemiology and mode of transmissions. Journal OftheAmerican Medical Association 99: 795—801.
Mooser, Herman. 1932. Essai sur 1’histoire naturelie du typhus exanthematique. Archive de VInstitut Pasteur de Tunis 21: 1-19.
Williams, C. L. 1949. The control of murine typhus with DDT. Military Surgeon 104: 163—7.
Zinsser, Hans, and M. R. Castaneda. 1932. Studies on typhus fever IX. On the serum reactions of Mexican and European typhus rickettsia. Journal of Experimental Medicine 56: 455-67.