Encephalitozoonosis in arctic lemmings.

Encephalitozoonosis was identified for the first time in arctic lemmings (Dicrostonyx stevensoni and crosses of D. stevensoni and Dicrostonyx rubricatus). The most common clinical findings were circling, torticollis, posterior paralysis, depression, blindness and death related to parasitic granulomas in many tissues. Granulomas were most frequent in the central nervous system, but were seen in many other tissues throughout the body. Granulomas were characterized by collections of macrophages and varying numbers of lymphocytes and neutrophils with or without necrosis of parenchymal tissue. Most granulomas contained protozoon cysts with ultrastructural characteristics of Encephalitozoon cuniculi. Protozoon cysts were seen in vascular endothelium in many tissues accompanied by minimal or no inflammatory reaction.