Demonstration of equine herpesvirus-1 gene expression in the placental trophoblasts of naturally aborted equine fetuses.

Equine herpesvirus-1 (EHV-1) infection was demonstrated in the lung tissue of seven aborted fetuses by immunohistochemical labelling and polymerase chain reaction. The placentas of the fetuses were also examined by non-isotopic in-situ hybridization for the EHV-1 glycoprotein B (gB) gene. Positive hybridization signals were observed in the cytoplasm of trophoblasts, especially in microcotyledons, of all seven placentas, and in villous epithelium of the allantochorion of six placentas. Despite the presence of EHV-1 RNA, EHV-1 antigens were not detected in placentas by immunohistochemical examination. The present study represents the first in-vivo demonstration of the EHV-1 gene in equine trophoblasts. The findings suggest direct cell-to-cell spread of EHV-1 from endometrial cells to trophoblasts.