Toxoplasma gondii in Iowa sows: comparison of antibody titers to isolation of T. gondii by bioassays in mice and cats.

Hearts of 1,000 pigs killed at an abattoir in Iowa were bioassayed for the prevalence of tissue cysts of Toxoplasma gondii. One hundred grams of cardiac muscle from each pig was homogenized, digested in pepsin solution, and bioassayed in 10 mice. Five hundred grams of heart tissue from each of a subset of 183 pigs was also bioassayed in cats. Serum collected from the heart from each pig was assayed for anti-T. gondii antibodies in the modified agglutination test using formalin-fixed whole tachyzoites. Anti-T. gondii antibodies were found in 22.2% of pigs. Viable T. gondii was isolated from a total of 170 pigs; from 50 hearts by bioassay in mice, from 58 hearts by bioassay in both mice and cats, and from 62 pigs by bioassay in cats only. The success of isolation in cats (65.6%) was approximately twice that in mice (31.7%). Percentage of isolations of T. gondii with respect to reciprocal antibody titers (in parentheses) in pigs was: 3.7% (< 20), 37.1% (20), 38.1% (40), 60% (80), 75% (200), 77% (400), 83% (800), and 75.8% (> or = 2,000 to 16,000).