A case of equine abortion caused by Encephalitozoon sp.

A Lippizan mare aborted a male fetus a few days before the expected foaling date without showing any clinical sings. Focal lympho-histiocytic hepatitis in the foal and multiplex focal lympho-histiocytic villitis accompanied by villus necroses and marked hypertrophy of chorionic epithelial cells in the arcades were observed. Elongated nucleated organisms were seen in groups in vacuoles or solitarily located in the cytoplasm of the chorionic epithelial cells. The organisms were in large numbers and often extracellularly in areas of villitis and villus necroses. They were Gram-positive, stained with haematoxylin and eosin (HE), periodic acid-Schiff (PAS) and Giemsa, weakly with Warthin-Starry silver stain but not with Gömöri's methenamine-silver stain. By ultrastructural and immunohistochemical examinations, the organisms were identified as microsporidia belonging to the genus Encephalitozoon. No Encephalitozoon organisms were detected in the fetal organs. This is the first reported case of equine abortion induced by Encephalitozoon sp. in Europe. Although abortion induced by Encephalitozoon is rare, microsporidia should be considered a differential diagnosis for intracellular organisms observed in the chorionic epithelial cells of horses.