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. Clinical signs in animals are not well documented. Diagnosis is based on serology and PCR. Doxycycline can be used for treatment if clinical signs are present.
Epidemiology of Murine Typhus in Animals
Murine typhus 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. Known to occur worldwide, there are current foci of human cases of murine typhus in southern Texas, California, and Hawaii. The disease is thought to be underreported.
Clinical Findings in Murine Typhus in Animals
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.
Diagnosis of Murine Typhus in Animals
Based on serology and PCR
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 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 sensitivity in assessing canine and feline infection is poor because the animals may not exhibit clinical signs during periods of rickettsemia, making it difficult to determine the optimal time for assessment. PCR can also be run on fleas obtained from pets to guide in documenting presence of typhus agents.
Treatment of Murine Typhus in Animals
Doxycycline can be used if clinical signs are present
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 mg/kg every 12 hours, or 10 mg/kg every 24 hours, 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.
Zoonotic Risk of Murine Typhus
R typhi is a zoonotic pathogen. Serologic evidence of exposure or past infection in dogs or cats is consistent with a heightened risk of human infections in a given area, although serology cannot pinpoint which rickettsial organism is present. Flea control for pets is an essential component of disease control. A role as a possible reservoir for infection has been suggested for cats; however rats and opossums are much more important hosts of the bacteria and sources of the infected fleas. 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.
Key Points
Murine typhus is a flea-transmitted zoonosis that is concentrated in a few foci in several states in North America.
Companion animals show no or few signs of disease but can host fleas that can be a source of spillover infection in people.
Reducing exposure to rats, opossums, and fleas are all means to reduce risk of transmission of murine typhus to people.
For More Information
The Companion Animal Parasite Council has guidelines on fleaborne rickettsiosis.
