Transplacental Transmission of Theileria equi Is Not a Common Cause of Abortions and Infection of Foals in Israel

SIMPLE SUMMARY: Theileria equi is a parasite of horses that is mainly transmitted by ticks but has also been reported to be transmitted from infected mares to their foals during pregnancy. This type of transmission may lead to abortion or to the birth of sick or infected foals. Little data are available regarding the magnitude of this type of transmission, although T. equi is considered to be a major cause of abortion in some areas. The aim of this study was to determine if T. equi is often transferred from mares to foals in an area where this parasite is abundant. We found that although the majority of aborting mares carried the parasite, none of the aborted fetuses were infected. Further, in a farm where all mares were infected, only one foal was infected by 6 months of age, and that infection was probably not from its dam. Although the number of inspected animals was small, our findings suggest that T. equi is not frequently transferred to foals during pregnancies of carrier mares. ABSTRACT: Although the main route of transmission of Theileria equi is through tick feeding, transplacental transmission is also possible and may lead to abortion, or to the birth of a sick or carrier foal. The aim of this study was to evaluate the role of T. equi as a cause of abortions in Israel and the risk of foals being infected at a young age. Eight aborting mares were serologically evaluated for exposure to T. equi via the immunofluorescence antibody test (IFAT) and their aborted fetuses were evaluated using PCR and qPCR. In addition, five mares and their foals (aged 4–6 months) from a highly endemic farm were tested for T. equi infection using IFAT, PCR and qPCR. Five of the eight aborting mares were seropositive for T. equi; however, none of the aborted fetuses was infected. All five mares from the endemic farm were subclinically infected with T. equi. Of their five foals, one was infected, with relatively high parasitemia and different parasite genotype than its dam’s, suggesting another source of infection. The results of this study suggest that transplacental transmission of T. equi is not common and does not appear to be a prominent cause of abortion in chronically infected mares.