Detection of Toxoplasma gondii-like oocysts in cat feces and estimates of the environmental oocyst burden

OBJECTIVE: To estimate the analytic sensitivity of microscopic detection of Toxoplasma gondii oocysts and the environmental loading of T gondii oocysts on the basis of prevalence of shedding by owned and unowned cats. DESIGN: Cross-sectional survey. SAMPLE POPULATION: 326 fecal samples from cats. PROCEDURES: Fecal samples were collected from cat shelters, veterinary clinics, cat-owning households, and outdoor locations and tested via ZnSO(4) fecal flotation. RESULTS: Only 3 (0.9%) samples of feces from 326 cats in the Morro Bay area of California contained T gondii-like oocysts. On the basis of the estimated tonnage of cat feces deposited outdoors in this area, the annual burden in the environment was estimated to be 94 to 4,671 oocysts/m(2) (9 to 434 oocysts/ft(2)). CONCLUSIONS AND CLINICAL RELEVANCE: Despite the low prevalence and short duration of T gondii oocyst shedding by cats detected in the present and former surveys, the sheer numbers of oocysts shed by cats during initial infection could lead to substantial environmental contamination. Veterinarians may wish to make cat owners aware of the potential threats to human and wildlife health posed by cats permitted to defecate outdoors.