Sarcocystis Infections in River Otter (Lontra canadensis) in Michigan

Abstract

Sarcocystis infections are common in the muscles of herbivores but were, until recently, considered relatively rare in carnivores. Little is known of sarcocysts in the muscles of river otters in the United States. In a previous epidemiologic study of Toxoplasma gondii infections in North American river otters (Lontra canadensis) from Michigan in the 2018 and 2019 harvest season, Sarcocystis DNA was found in 34 (27.4%) of 124 otter muscles. Tongues from these 34 PCR-positive samples were further examined here for Sarcocystis species. An additional batch of frozen 62 samples collected at the end of the season was also tested for Sarcocystis herein. Morphologically, sarcocysts were studied in 23 otters (13 of 34 PCR-positive samples from the first batch and 10 of 62 samples of batch 2) in compression smears and paraffin-embedded histologic sections stained with hematoxylin and eosin. Morphologically, at least 2 different kinds of sarcocysts were identified, 1 with a smooth sarcocyst wall and the second with villar protrusions. By transmission electron microscopy, sarcocysts from 1 otter were similar to Sarcocystis caninum. Morphologically, sarcocysts from the river otter were different from the European otter (Lutra lutra). Sequencing amplification products from 18S rRNA, 28S rRNA, and cox1 genes, suggested S. caninum-like, Sarcocystis svanai-like, and Sarcocystis sp. We detected a third, potentially undescribed species, in 3 otters. Genetic markers for conclusive differentiation of Sarcocystis spp. from mustelids should be developed. The samples in the present study had degraded; better preserved samples are needed for further morphologic studies. This is the first report of S. caninum-like, S. svanai-like, and Sarcocystis sp. in the river otter in the United States