Prevalence of viable Toxoplasma gondii tissue cysts and antibodies to T. gondii by various serologic tests in black bears (Ursus americanus) from Pennsylvania.

During the hunting season of 1993, hearts from 28 black bears (Ursus americanus) from Pennsylvania were examined for Toxoplasma gondii infection. Serum samples from heart blood were examined for T. gondii antibodies by the use of the modified agglutination test (MAT), the Sabin-Feldman dye test (DT), the latex agglutination test (LAT), and the indirect hemagglutination test (IHA). One-hundred grams of myocardium from each bear were bioassayed in mice. Approximately 500 g of myocardium from 11 bears were fed to 11 cats, and feces from those cats were examined for T. gondii oocysts. Toxoplasma gondii MAT antibodies (> or = 1:40) were found in 22 bears in titers of 1:40 (4 bears), 1:80 (3 bears), 1:160 (7 bears), 1:320 (4 bears), and > or = 1:2,000 (4 bears). Antibodies to T. gondii by DT (> or = 1:10), LAT (> or = 1:32), and IHA (> or = 1:64) tests were found in 21, 9, and 6 bears, respectively. All 6 bears that did not have T. gondii antibodies in MAT were also negative in DT, IHA, and LAT. Viable T. gondii was isolated from 3 bears by bioassays in mice and from an additional 7 bears by bioassays in cats. All 10 bears that had viable T. gondii had MAT and DT antibodies but only 6 and 5 of them had antibodies by LAT and IHA, respectively.