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Epidemic Typhus Associated with Flying Squirrels -- United States

Since 1976, 30 cases of illness caused by Rickettsia prowazekii, the causative organism of epidemic typhus, have been documented serologically among residents of the United States (1-3). These cases have been unusual in that, unlike classic louse-borne epidemic typhus, they have occurred sporadically, primarily in rural or suburban areas of the eastern United States. Ten of the 30 cases have occurred in Georgia, four in Virginia, three in North Carolina, two in Pennsylvania, two in Indiana, and one each in California, Illinois, Maryland, Massachusetts, Ohio, New Jersey, New York, Tennessee, and West Virginia. Twenty-one of the 30 cases have occurred during the coldest months of the year--December, January, and February (Figure 1).

Of the 30 patients with sporadic R. prowazekii infection, 73% have been greater than or equal to 20 years of age and 50% have been male. Clinically, patients have presented with fever (100%), headache (81%), skin rash (66%), confusion (44%), and myalgia (42%). The skin rash has been characterized as maculopapular, usually involving the trunk and spreading to the extremities. Seventy-six percent of patients have received therapy with tetracycline or chloramphenicol; recovery has been much more rapid among these patients than among those not receiving appropriate antibiotics. However, no patient with sporadic R. prowazekii infection, regardless of antibiotic therapy, has died.

In 10 of 18 cases of sporadic R. prowazekii infection for which information has been available, flying squirrels, or nests consistent with those observed for flying squirrels, have been found in a home or building frequented by the patient. In one report, the southern flying squirrel, Glaucomys volans, was readily trapped in the environs of the patient in six of seven cases (2). This rodent inhabits the eastern United States, frequently nests in the attics of houses during the winter, and is a known host of R. prowazekii (4). It is presumed that infection is acquired from this animal, although the mechanism of transmission is unknown. One case of typhus occurred in California, where G. volans is absent. Glaucomys sabrinus, a close relative of G. volans, is present in California, but serologic studies of this species for antibody to R. prowazekii have been initiated only recently.

It has long been assumed that the causative agent of epidemic typhus existed only in the man-louse-man cycle, and that patients who had recovered from typhus constituted the reservoir of R. prowazekii in inter-epidemic periods (rickettsemia develops in Brill-Zinsser disease, the recrudescent form of R. prowazekii infection). Under this assumption, eradication of epidemic typhus on a global scale would be theoretically possible, since few patients with Brill-Zinsser disease would be alive after long inter-epidemic periods. The finding of sporadic R. prowazekii infecton and the existence of a sylvan reservoir of this rickettsial agent, therefore, have important implications concerning the perpetuation of epidemic typhus in humans. Since none of the patients with sporadic epidemic typhus have been infested with body lice, the possibility that sporadically acquired infection can precipitate outbreaks of epidemic typhus remains unexplored. Whether flying squirrels and/or other mammalian hosts were infected with R. prowazekii before the evolution of epidemic typhus in humans, or whether the reverse is true, is also unknown.

Since the causative organism has yet to be isolated from a human with sporadic R. prowazekii infection and since the mechanism of transmission of this disease has not been elucidated, CDC is attempting to identify as many cases of this disease as possible. Therefore, physicians who encounter patients with a rickettsial-like illness (fever, headache, myalgia, and skin rash) during the colder months are encouraged to report these cases to CDC through their local and state health departments. Reported by Div of Viral Diseases, Center for Infectious Diseases, CDC.


  1. McDade JE, Shepard CC, Redus MA, Newhouse VF, Smith JD. Evidence of Rickettsia prowazekii infections in the United States. Am J Trop Med Hyg 1980;29:277-84.

  2. Duma RJ, Sonenshine DE, Bozeman FM, et al. Epidemic typhus in the United States associated with flying squirrels. JAMA 1981;245:2318-23.

  3. CDC, unpublished data.

  4. Bozeman FM, Masiello SA, Williams MS, Elisberg BL. Epidemic typhus rickettsiae isolated from flying squirrels. Nature 1975;255:545-7.

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