Molecular characterization of Sarcocystis spp. as a cause of protozoal encephalitis in a free-ranging black bear

Abstract

A free-ranging juvenile male black bear (Ursus americanus), found dead in Alberta, Canada, had severe nonsuppurative encephalitis. Lesions in the brain were most severe in the gray matter of the cerebral cortex, and included perivascular cuffs of lymphocytes and plasma cells, areas of gliosis that disrupted the neuropil, and intralesional protozoan schizonts. The left hindlimb had suppurative myositis associated with Streptococcus halichoeri. Immunohistochemistry and molecular analyses (PCR and sequencing of 4 discriminatory loci: 18S rDNA, ITS-1 rDNA, cox1, rpoB) identified Sarcocystis canis or a very closely related Sarcocystis sp. in the affected muscle and brain tissues. The main lesion described in previously reported cases of fatal sarcocystosis in bears was necrotizing hepatitis. Fatal encephalitis associated with this parasite represents a novel presentation of sarcocystosis in bears. Sarcocystosis should be considered a differential diagnosis for nonsuppurative encephalitis in bears.

Keywords: Canada; Sarcocystis; Ursidae; disease; encephalitis; pathology; wildlife.

Figure 1.

Sarcocystosis in a free-ranging black bear (Ursus americanus). A. Myocytes are variably swollen, fragmented, and contain mineral consistent with degeneration. Myocytes occasionally contain tissue bradyzoites consistent with Sarcocystis spp. (arrow). H&E. Original objective 20×. B. Severe perivascular cuffs of lymphocytes and plasma cells with adjacent gliosis of the neuropil indicative of nonsuppurative encephalitis and a degenerate Sarcocystis spp. schizont (arrow) in the brain. H&E. Original objective 20×. C. Sarcocystis spp. schizont in the brain. H&E. Original objective 60×. D. Immunohistochemistry for Sarcocystis neurona in the brain shows moderately intense immunoreactivity of a schizont. Original objective 100×.