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Outbreak of Murine Typhus -- Texas

A cluster of cases of murine (endemic) typhus has been reported from Texas. From October 25 to November 11, 1982, five persons became ill with fever (temperature greater than or equal to 40C ( greater than or equal to 104F)) (all five patients), headache (three patients), and myalgia (two patients). On the 4th or 5th day of illness, three patients developed a macular rash that began on the trunk and spread to the extremities. Blood specimens obtained on December 16, 1982, from three patients demonstrated indirect fluorescent antibody titers of 1:512 or greater to typhus-group rickettsiae; cross-absorption studies performed at CDC using antigens to Rickettsia typhi (the causative organism of endemic typhus) and R. prowazekii (the causative organism of epidemic typhus) indicated the former as the cause of the elevated titers. No serum specimens were obtained from the other two patients. Four patients received appropriate antimicrobial therapy with tetracycline; all five recovered without sequelae.

Three patients--a 27-year-old male, a 25-year-old female, and a 6-year-old female--lived in a house that had been unoccupied for 5 years before being moved in July 1982 to its present site on a peanut farm in Comanche County in northcentral Texas. The other two cases occurred in a 24-year-old female who visited this family at their home every 1 or 2 weeks and a 48-year-old female, the grandmother of the 6-year-old, who lived one-quarter mile away and visited the house at least once a month. Inspection of the house revealed holes in the roof, walls, and floors, and a large space beneath the house. Family members had heard rodents in the attic before the outbreak, and a mouse had recently been killed in the bathroom. Two or 3 weeks before the outbreak, rat poison had been placed inside the house. Five cats, present in the home before the outbreak, died during the outbreak period, four of unexplained causes, one in an accident. The cats slept indoors and had fleas. The family also owned three dogs, which usually slept underneath the house; they remained healthy during the outbreak period. None of the patients recalled being bitten by fleas.

An exterminator visited the house on November 19, 1982, and applied insecticide and rat poison. No further illnesses among family members or visitors to the house have been reported. Reported by T Ford, Region 4, CR Webb, Jr, MD, State Epidemiologist, Texas Dept of Health; Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The causative agent of murine typhus--R. typhi (formerly R. mooseri) is maintained in nature by commensal rats and their ectoparasites. Humans acquire the infection through contact with the infected rat flea, Xenopsylla cheopis. The flea defecates while feeding, and irritation from the bite causes the host to scratch and thus deposit rickettsiae from the feces into the wound. Other mammals and ectoparasites, including cats and cat fleas, have been found infected with R. typhi, although these infections, as well as those in humans, are not important in maintaining the agent in nature.

In the early 1940's, 2,000-5,000 cases of murine typhus were reported annually in the United States, most in the Southeastern and Gulf Coast states. Incidence of the disease declined when rat control programs were instituted after World War II. Currently, murine typhus is not reportable in most states, and only 60-80 cases are reported annually to CDC. In recent years, approximately 80% of these cases have been reported from Texas. In 1981, the most recent year for which information is available, Texas reported 49 cases of murine typhus, with treatment information available for 43; 39 (91%) patients received appropriate therapy with tetracycline or chloramphenicol. There were no deaths.

Although much information concerning the ecology of murine typhus is available (1), unresolved issues remain. In this outbreak, for example, whether the cats or their fleas were involved in transmitting typhus to humans, whether they were uninvolved but also acquired infection, or whether their deaths were entirely unrelated to the outbreak could not be determined. (Dogs and dog fleas have not been found to harbor R. typhi.) Prompt reporting and investigation of similar outbreaks in the future might help resolve such issues.

The use of rat poison in the home 2-3 weeks before the outbreak may have precipitated the human illnesses. Rat fleas will seek alternative hosts when rodents are not available and thus may transmit the disease to man. In areas where murine typhus is known to occur, rat control programs should be preceded by applying insecticides to control these ectoparasites.

Reference

  1. Traub R, Wisseman CL Jr, Farhang-Azad A. The ecology of murine typhus--a critical review. Trop Dis Bull 1978;75:237-317.



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