Francisella tularensis can infect several vertebrate species. Infection occurs through exposure to tick vectors or other biting insects; direct contact with blood, tissues, or fluids of infected mammals; ingestion of contaminated food or water; or by inhalation. In cats, disease severity can range from mild to fatal with nonspecific clinical signs that may include pyrexia, anorexia, lymphadenopathy, or oral ulcers. In this study, privately owned cats from Connecticut and New York were analyzed for the presence of F tularensis antibodies using microagglutination and indirect fluorescent antibody (IFA) staining methods. Of the 91 cats, 12 showed clinical signs of fever, lameness, anorexia, or fatigue, while the remaining 79 cats appeared healthy. Analysis of sera performed by using microagglutination revealed that 11 samples (21%) contained antibodies to F tularensis. Using IFA staining on the same samples revealed 22 (24%) to be positive for antibodies. Higher antibody titers were found by using IFA analysis (1:80 to 1:640) than by microagglutination methods (1:80 to 1:160). There was good agreement between results found in both tests (73% concordance). No DNA of F tularensis was detected in the sera of the 24 antibody-positive cats, leading the authors to believe the antibodies found were the result of prior exposure rather than active infection and that serologic evidence of exposure may not be tightly linked to infection. In addition, the authors found minimal serologic cross-reactivity between F tularensis and 2 other organisms that occur widely in the northeastern United States, Borrelia burgdorferi and Anaplasma phagocytophilum. The authors conclude that tularemia should be considered in cats with unexplained fever that are living in tick-infested areas where this disease is endemic. Either microagglutination or IFA tests can be used for general screening, but the authors found it easier to identify positive antibody reactions in fluorescein-stained specimens.

COMMENTARY: This article clearly illustrates the risk of exposure to free-roaming cats for this highly zoonotic infectious disease. The authors speculate that the lack of reported cases in humans in the United States is probably due, at least in part, to lack of awareness, underdiagnosis, or subclinical infections. Armed with the information presented here, practitioners can be more alert to the risks for their outdoor feline patients and keep clients well-informed about protecting these pets. While keeping a cat indoors is not always feasible, practitioners can still encourage tick control and spaying/neutering (to reduce roaming behavior) for cats that continue to go outside. In addition, this article helps alert practitioners to the need for caution when handling cats with suspected tularemia in order to reduce chance of exposure to themselves and their staff.

Detection of antibodies toFrancisella tularensis in cats. Magnarelli L, Levy S, Koski R. RES VET SCI 82:22-26, 2007.