Serological prevalence of Toxoplasma gondii and its association with abortion in sheep in Saudi Arabia

Abstract

The purpose of this study was to investigate serological prevalence and titers of anti-Toxoplasma gondii antibodies in ewes following waves of abortion and stillbirths in a commercial flock in Riyadh, Saudi Arabia. Serum samples from 168 aborted ewes and 52 breeding rams, were tested for toxoplasmosis using an indirect enzyme-linked-immunosorbent assay (ELISA) and indirect haemagglutination test (IHA). 71 randomly sampled sheep from an abortion-free flock (60 ewes and 11 rams) were also tested, which served as controls. 149 (88.7%) ewes and 42 (80.8%) breeding rams from the flock where abortions and stillbirths occurred were positive for anti-T. gondii antibodies by ELISA. 155 ewes (92.3%) and 44 rams (84.6%), including all of the ELISA positive cases, were also positive by indirect haemagglutination test (IHA). More than 80% of the ELISA-positive ewes had O.D. exceeding 100% and nearly 25% of them had O.D. of ≥150%. The IHA results, on the other hand, indicated that more than 75% of the seropositive ewes had antibody titers ≥1:1024, including 58 (37.4%) ewes with IHA titer ranging between 1:4096-1:8192 Pyrexia, depression and vaginal discharge were recorded in some ewes shortly prior to abortion. Post-mortem examination of 5 aborted fetuses revealed blood-stained fluid in the abdominal and thoracic cavities and small inflammatory and necrotic foci in the brain, liver and lungs while the placenta was reddish and friable, and its cotyledons were speckled with small whitish foci of necrosis and mineralization. T. gondii tachyzoites were demonstrated in placental sections of two ewes. By contrast, only 7 (9.9%) out of 71 randomly sampled sheep from an abortion-free flock (60 ewes and 11 rams), were positive for anti-T. gondii antibodies by ELISA and 6 (8.5%) by indirect haemagglutination (IHA) test and most of these had significantly lower titers compared to the flock where abortions and stillbirths were recorded. These results constitute the first detailed serological study of ovine toxoplasmosis in Saudi Arabia and strongly implicate toxoplasmosis as the cause of the abortions and stillbirths in these sheep.