Theileria equi infection causing abortion in a mare in Brazil

The aim of this report was to confirm the cause of abortion to be Theileria equi acquired transplacentally in a mare in Federal District, Brazil. The aborted fetus showed a high parasitemia of erythrocytes (80%) by the oval and Maltese cross forms of T. equi. Necropsy of the fetus demonstrated congestion of organs, jaundice, anemia and pronounced spleno- and hepatomegaly. Twelve breeding mares, including the one that aborted and her fetus, tested positive for T. equi infection by universal and multiplex PCR assay. The absence of histopathologic changes such as inflammation and necrosis in the placenta and fetal tissues as well as the negative microbiological results and negative serology for Leptospira spp. in the mare that aborted were important to exclude other infectious agents that may be involved in equine abortion. This report highlights the transplacental transmission of T. equi infection in horses in endemic areas and reinforces the importance of investigating equine theileriosis as a possible cause of abortion in mares.