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 <i>T. gondii</i> 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) (<i>n</i> = 1035 sheep) and by a polymerase chain reaction (PCR) (<i>n</i> = 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 <i>T. gondii</i> 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 <i>T. gondii</i> by mouse bioassay. A viable <i>T. gondii</i> 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 <i>T. gondii</i> has been decreasing in sheep from China. However, <i>T. gondii</i> remains present in sheep herds and should not be ignored.