Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 18, 1994
Publication Date: N/A
Interpretive Summary: Infection by the protozoan parasite Toxoplasma gondii is widespread in livestock and humans. It causes mental retardation and loss of vision in children and abortion in livestock. Humans become infected with T. gondii by ingesting uncooked meat infected with tissue cysts and food and water contaminated with oocysts from infected cat feces. Among food animals, pigs are considered the most important meat source of T. gondii for humans. Scientists at the Beltsville Agriculture Research Center and Iowa State University have found viable Toxoplasma tissue cysts from 17% of 1000 adult pigs from Iowa. The observations indicate that the T. gondii infection in pigs is common in Iowa. This data will be useful for planning control strategies to reduce or eliminate infection in pigs.
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 were 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 170 pigs; from 108 pigs by bioassays in mice, and from 62 additional pigs by bioassays in cats. The rate 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 parenthesis) in pigs was: 3.7% (< 20), 37.1% (20), 38.1% (40), 60% (80), 75% (200), 77% (400), 83% (800), and 75.8% (greater than or equal to 2,000 to 16,000).