Epidemiologic findings on a swine farm with enzootic toxoplasmosis.

A farm in Illinois had swine with enzootic Toxoplasma gondii infections. Ninety-five of 99 pigs had antibody against T gondii by the modified agglutination test; modified agglutination test titers were less than 1:10 (4 pigs), 1:10 (15 pigs), 1:20 (12 pigs), 1:40 (10 pigs), 1:80 (20 pigs), 1:160 (11 pigs), 1:320 (12 pigs), 1:640 (9 pigs), and greater than or equal to 1:1,280 (6 pigs). To trace the route of infection, Toxoplasma-free pigs were introduced into the farm and were evaluated serologically at various intervals. Analysis of data derived from these tracer pigs indicated that cannibalism was a major source of T gondii infection in the pigs.