Histopathologic study of experimental Sarcocystis hemionilatrantis infection in fawns

Mule deer fawns (Odocoileus hemionus hemionus) inoculated with sporocysts of Sarcocystis hemionilatrantis became infected, developed clinical signs of disease, and died, due to the infection itself or from intercurrent pneumonia. Clinical signs were first noticed 18 days after infection and fawns died from postinfection days 27 to 63. Histopathologic examination revealed early lesions in skeletal muscle which consisted of perivascular necrosis with mononuclear and neutrophilic cell infiltration, accompanied by edema, degeneration, and focal necrosis of muscle. Subsequently, this reaction subsided and the cellular infiltrate dissipated. An infected macrophage usually remained in the vacuolated muscle space; each macrophage was surrounded by a clear halo. Developing Sarcocystis schizonts were identified in the cytoplasm of the macrophages, and the cytoplasmic membrane eventually ruptured releasing merozoites. The merozoites then developed into typical muscle cysts. Results of the present study indicated that S hemionilatrantis is a pathogen of mule deer under experimental conditions. Pathogenicity should be investigated to determine if S hemionilatrantis causes death or debilitation in wild mule deer under natural conditions.