Epizootiologic investigations on a sheep farm with Toxoplasma gondii-induced abortions

During the lambing season of 1983/1984, 8 of 44 purebred Hampshire ewes on a farm in Knoxville, Md had reproductive problems. In at least 4 of these ewes, the problem was attributed to toxoplasmosis. Necrosis and Toxoplasma gondii tachyzoites were found in placental specimens from 3 ewes. Agglutinating antibody to T gondii, at a titer of 1:80, was found in pleural fluids of both fetuses aborted from 1 ewe; this ewe had an antibody titer of 1:6,400 at the time of abortion. In another ewe, the diagnosis was confirmed by the isolation of T gondii from the placenta and 1 of her lambs. Of numerous free-roaming adult cats on the farm, 16 were trapped, euthanatized, and examined for T gondii. Agglutination antibody to T gondii, at titers of 1:4 to 1:64, was found in serum samples from all the cats. Toxoplasma gondii was isolated from the brain and skeletal muscles of 9 of the cats, and from the feces of 1 cat. Blood samples obtained from all 78 sheep on the farm 6 months after the episode of abortion were examined for antibody to T gondii. Agglutinating antibody titers to T gondii were less than 1:16 in 46 sheep, 1:16 in 16, 1:64 in 12, 1:256 in 2, 1:024 in 1, and 1:4,096 in 1. Analyses of serologic data in sheep of various age groups suggested that the Toxoplasma infection was acquired sporadically, probably from feed contaminated with oocysts.