HISTOPATHOLOGICAL AND IMMUNOFLUORESCENT STUDIES ON TRANSPLACENTAL INFECTION IN EXPERIMENTALLY-INDUCED ABORTION BY EQUINE ARTERITIS VIRUS

Five pregnant mares, at between 6 and 8 months gestation, were experim entally infected with the Bucyrus strain of equine arteritis virus (EA V). Of the five mares, four aborted and one died. The pathogenesis of the abortions was studied, using histopathologic techniques, tissue im munofluorescence and virus isolation. Common microscopic lesions in th e maternal reproductive organs indicated myometritis with a degenerati on of the myocytes and an infiltration of the mononuclear cells. Epith elial cells of the endometrial gland showed sporadic degeneration. Les ions in the fetal tissue included an atrophy of the lymphoid follicles in the spleen and lymph nodes with degenerated lymphocytes. The place ntae were oedematous and degenerated fibroblasts were observed in the subvillous layers. Immunofluorescence detected EAV antigen in the myom etrium and the endometrial gland in the dams, in the subvillous layer of the placentae, and in the aborted fetuses. EAV was recovered from t he maternal uteri, placentae and fetuses. The placentae yielded the gr eatest amounts of the virus. Transplacental infection of the fetus was clearly demonstrated in the EAV infection.