A microscopic mystery infecting wild British Columbian bears

In 2008, the death of a captive black bear drew the attention of wildlife researchers at the Canadian Wildlife Health Cooperative British Columbia (CWHC BC). The bear had extensive liver damage caused by a parasite never before recorded in BC bears. By 2016, this parasite was detected in numerous wild bears. Over a decade later, what do we know now?

Bears are critical to healthy British Columbian ecosystems as they help with nutrient cycling and by keeping prey populations in check. To facilitate management of wild populations, we need a better understanding of the diseases they face. This is especially true when new concerns or diseases arise. While Sarcocystis spp. are not unknown parasites, they had not yet been detected in BC bears. So, we began an investigation to understand how this small parasite is impacting BC bears.

To answer this question, we evaluated all previous black bear and grizzly bear cases submitted to the BC provincial diagnostic lab from 2007-2019 for evidence of infection (parasite presence), or disease (inflammation or organ damage). To do this, we looked at bears’ liver, brain, and muscle tissues under a microscope for parasite life stages and any signs of inflammation or tissue damage. To determine which species of parasite was present, we also sequenced and analyzed the parasite’s DNA.

It turned out that this particular culprit was in fact a small, single-celled parasite– Sarcocystis canis, which has previously been identified in bears and dogs. This parasite can result in illness in bears by causing inflammation to the liver, brain, or muscle. In some cases, we identified bears infected with Sarcocystis spp. in the muscle, without associated inflammation. We found that of the 102 bears assessed, 40% had evidence of Sarcocystis spp. infection. Bears were infected with a wide distribution across BC. Yearling bears were more likely to be infected, and only the cubs died of sarcocystosis.

What does this mean for wild bears in BC and should we be concerned? While Sarcocystis spp. infection was far more common than originally anticipated, it did not typically cause death, except in cubs. We unfortunately do not know much about the parasite’s life cycle or how the bears became infected. Since younger bears had a higher risk of infection, Sarcocystosis may be an important disease particularly for yearlings and cubs.

Despite our investigation here, this story of bears and parasites in BC does not end quite yet! More research is required to provide a better understanding of the risks that sarcocystosis poses to wild BC bears in order to help inform conservation efforts and maintain a healthy ecosystem.

For more information, a summary of this study can be found here, with the full research article published at the Journal of Wildlife Diseases.

Article by Lisa Lee and Kaylee Byers