Toxoplasmosis in Sheep Caused by Toxoplasma gondii Clonal Type I

Ovine toxoplasmosis has a significant negative impact on sheep farming, and abortion is the main clinical manifestation. The objective of the present study was to survey ovine toxoplasmosis and assess its potential harm T. gondii in sheep. Sheep serum or heart fluid was collected from 1035 sheep, along with the tissue or blood samples collected from 164 of them. We investigated ovine toxoplasmosis by a modified agglutination test (MAT) (n = 1035 sheep) and by a polymerase chain reaction (PCR) (n = 164 sheep) in China. The results showed that 75 sheep were seropositive (titer ≥ 1:100), with a prevalence of 7.2%, as assessed by MAT. The molecular prevalence of T. gondii in sheep was 16.4% (27/164), as assessed by PCR. From these 164 tissue or blood samples, 22 tissues and 2 blood samples were selected in order to isolate T. gondii by mouse bioassay. A viable T. gondii strain (TgSheepCHn15, ToxoDB #10) was isolated from sheep tissues in the veterinary clinic. This strain was avirulent for Swiss mice, and the survival time of mice was 97 ± 31 days. This is the first instance of the isolation of a Type I strain from sheep with avirulence in mice. The prevalence of T. gondii has been decreasing in sheep from China. However, T. gondii remains present in sheep herds and should not be ignored.