Enzootic Toxoplasmosis in Sheep in North-Central United States

Of 1,564 serum samples from adult ewes from 33 farms in Iowa, Minnesota, South Dakota, Kansas, and Nebraska where toxoplasmosis-induced ovine abortions had been diagnosed, 65.5% were found positive for Toxoplasma gondii antibodies using the modified agglutination test. Toxoplasma gondii antibody titers of ewes were: 4,096 (13.8%). Thus, 28.3% of sheep had high titers (>1,024) indicating recently acquired T. gondii infection. On certain farms, up to 95% of ewes were seropositive. Prevalence of T. gondii antibodies increased with age of the ewe. Of 665 ewes, 53.6% of 1-yr-old ewes were seropositive (titers > 64) versus 75% of 5-yr-old ewes. Results indicate that T. gondii infection in sheep in the United States is widespread.