T. gondii is prevalent in most areas of the world and is of veterinary and medical importance, because it may cause abortion or congenital disease in its intermediate hosts. In sheep, T. gondii is an important cause of abortion, which can result in considerable economic losses. Herbivores acquire infection mainly by the ingestion of oocysts in water or contaminated food. Seroprevalence of T. gondii in sheep have been reported extensively in different countries and the positive rates ranged from 3% to 95%. The diagnosis of toxoplasmosis can be made by means of indirect methods such as serological evaluation to detect specific antibodies. The hypothesis that primary infection protects against reinfection is the basis for many farmers not to discard sheep with a history of abortion. However, recent studies have suggested that sheep persistently infected with T. gondii may transmit the infection congenitally more frequently than expected. Ewes persistently infected with c transmitted the infection congenitally, possibly due to an acute relapse process. This result shows that the immunity acquired in the primary infection did not protect the ewes against future T. gondii reinfections. The experimental T. gondii reinfection triggered severe reproductive alterations (locomotive changes, malformations, stillbirths and disability) in Santa Inês ewes primarily infected at different pregnancy stages. Therefore, congenital T. gondii infection was common when ewes were chronically infected prior to pregnancy, with or without reinfection during at various stages of gestation.