Sarcocystis infections in river otter (Lontra canadensis) in Michigan

Authors: Dubey, Jitender; GUPTA, ADITYA - Oak Ridge Institute For Science And Education (ORISE); KOTHAVALE, KIRAN - Henry A Wallace Center; COTEY, STACY - Michigan Technological University; REICHARD, MASON - Oklahoma State University; Rosenthal, Benjamin; CALERO-BERNAL, R. - University Of Madrid; GARCIA-GIL, M. - Spanish National Microscopy Centre

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2025
Publication Date: 8/7/2025
Citation: Dubey, J.P., Gupta, A., Kothavale, K., Cotey, S., Reichard, M., Rosenthal, B.M., Calero-Bernal, R., Garcia-Gil, M.L. 2025. Sarcocystis infections in river otter (Lontra canadensis) in Michigan. Journal of Parasitology. 111(4):516-525. https://doi.org/10.1645/25-25.
DOI: https://doi.org/10.1645/25-25

Interpretive Summary: Parasites in the genus Sarcocystis infect agricultural livestock and wildlife species, imposing risks to animal health. Some species also cause disease in people who have consumed contaminated water or meat. Scientists can now track which livestock pose risks to human health, and which wildlife pose risks to livestock health, using genetic assays. Here, USDA scientists discovered infections in more than 25% of tested river otters, which feed on aquatic life and are exposed to runoff from land. DNA sequencing indicated that their parasites resemble parasites infecting dogs and wolves; reassuringly, the parasites discovered in river otters do not resemble parasites known to cause human disease. These results will help biologists, parasitologists, wildlife services, and veterinarians track the spread of these parasites in natural conditions and diagnose disease in companion animals. The results alleviate concern that river otters harbor species of Sarcocystis that endanger livestock or human health.

Technical 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.