Encephalitozoon infection in a still-born foal

A stud Clydesdale foal was still-born near full term. Macroscopic examination revealed a normal placenta, pulmonary atelectasis and faint white mottling of the kidneys. Microscopically there was severe lymphoplasmacytic interstitial nephritis. Numerous organisms resembling Encephalitozoon cuniculi were present in the affected kidneys. The organisms occurred in the areas of inflammation as well as in the renal glomeruli and intracellular cysts in the renal tubular epithelial cells and exhibited Gram positive staining. Ultrastructurally the organisms possessed a polar vacuole and a spiral filament typical of Microsporidia. The organisms were not detected in sections of the other organs examined.