Feline toxoplasmosis: interpretation of diagnostic test results.

Based on seroprevalence studies, approximately 30% of the cats in the United States have been infected by T gondii. Cats are the only species that pass the environmentally resistant oocyst in feces. Sporulated oocysts are infectious to humans and the organism can cause significant disease in immunocompromised people and transplacentally-infected babies. Clinical illness including liver disease, lung disease, central nervous system disease, fever, and uveitis occur in some infected cats. Veterinarians need to be able to identify T gondii infection in cats because of potential public health risks and during the workup of clinical diseased cats. Oocyst shedding by cats is of short duration, but can be detected by fecal examination. There are currently no serological tests that can accurately determine when a cat has shed oocysts in the past. The combination of serological test findings, clinical signs of disease, exclusion of other causes, and response to anti-Toxoplasma drugs is required to make the diagnosis of antemortem++ clinical toxoplasmosis in cats.