THE MERCK VETERINARY MANUAL
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Murine Typhus

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Rickettsia typhi, the causative agent of murine typhus, and R felis are zoonotic pathogens maintained primarily in rodent reservoirs (rats, mice) that may also be associated with enzootic cycles involving opossums and domestic cats. Infection is transmitted to people and other animals through contact with infected fleas.

Infection in people is primarily thought to occur through exposure of abraded skin with infectious flea feces; aerosolization of infectious materials may occur in limited settings. Dogs and cats are presumably exposed in a similar fashion. Although known to occur worldwide, currently fewer than several hundred human cases of murine typhus are reported in the USA each year. Enzootic infection is the most commonly reported from southern Texas, California, and Hawaii, although the disease is believed to be under-reported.

Clinical illness associated with canine and feline infection with R typhi and R felis is not well documented, but evidence of exposure based on presence of antirickettsial antibodies has been noted, particularly in association with outbreaks of human disease. Although a role as a possible reservoir for infection has been suggested, particularly for cats, the importance of domestic animals in maintenance of enzootic cycles has not been well elucidated. Nonetheless, dogs and cats may, at a minimum, serve as a source of fleas that may pose a transmission risk to people. Regular flea control is recommended to reduce risk of flea-associated transmission to people.

An indirect fluorescent antibody (IFA) titer assessed in paired sera is preferred for serologic testing and is most commonly used in conjunction with environmental assessments around a human outbreak. There is some degree of antibody cross-reactivity with antibodies from other rickettsial infections, including R rickettsii, so assessments should ideally be made with paired sera. PCR of whole blood may also be used, but its utility in assessing canine and feline infection is unknown because the animals may not exhibit clinical signs during periods of rickettsemia, making it difficult to determine the optimal time for assessment.

In the absence of clinical signs, specific treatment is not recommended. If clinical illness associated with R typhi or R felis infection is suspected in a dog or cat, doxycycline may be administered at a dosage of 5–10 mg/kg/day, PO or IV, for 10–21 days. Animals should be provided with routine preventive treatments to control fleas. Control programs involving animal removal from an area of enzootic activity should be accompanied by pesticide treatment of the environment to prevent fleas feeding on people after the removal of preferred blood-meal hosts.

R typhi is considered a zoonotic pathogen. Serologic evidence of exposure or past infection in dogs or cats indicates a heightened risk of human infections in a given area, and flea control for pets is an essential component of disease control.

Last full review/revision March 2014 by Jennifer H. McQuiston, DVM, MS

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