What is Meningeal Worm and Why Does It Matter?
Meningeal worm is a parasitic roundworm that typically infects white-tailed deer, its natural host. In white-tailed deer, the parasite carries out its lifecycle and rarely causes illness. However, in caribou and other cervids, it causes severe neurological disease and death due to damage to the brain and spinal cord. Boreal caribou are listed as threatened in Canada and this parasite poses a significant risk to their conservation. In eastern parts of Canada, where overlap with infected white-tailed deer and caribou occurred, free-ranging caribou populations have gone extinct and reintroduction programs have failed due to this disease.
The Discovery
The first case of meningeal worm infection in Caribou in Alberta was found in June 2024 when a caribou was reported to the Northeast Alberta Caribou Program as behaving abnormally along a road in the Cold Lake Air Weapons Range. The caribou was found in emaciated body condition with severe neurological clinical signs including circling, ataxia, weakness and no fear of people. The animal was euthanized and a field necropsy was conducted. Histologic examination, performed by the Canadian Wildlife Health Cooperative (CWHC), revealed migratory tracts in the brain suggestive of migrating nematode larvae.
Initial molecular testing performed at the Animal Health Laboratory in Guelph was positive. However, their PCR test cannot distinguish between Parelaphostrongylus tenuis (P. tenuis) and P. andersoni, another related parasite known to be in Alberta, but not previously linked to neurologic disease. Given that P. tenuis had not been previously reported in the province, more rigorous testing was pursued to confirm our suspicions. Samples were sent to Dr. Richard Gerhold’s laboratory at the University of Tennessee Knoxville. Dr. Gerhold is a board certified veterinary parasitologist and an expert in Parelaphostrongylus spp. Additional PCR testing and sequencing at his lab verified the presence of P. tenuis in this case and subsequent cases.
Ultimately, five Boreal caribou between June 2024 and May 2025 and one moose investigated by Fish and Wildlife Stewardship in northeast Alberta in June 2025 have been confirmed positive for meningeal worm, making this the first documented occurrence of the parasite in Alberta.
Why This Matters for Caribou Conservation and Alberta Wildlife
Boreal caribou are already under pressure from habitat loss, climate change, and predation. The emergence of meningeal worm in their range poses another significant threat to their conservation. Treatment of this parasite is not possible in free-ranging populations, and a vaccine currently does not exist.
The presence of P. tenuis in Alberta also represents a threat to other wildlife species including moose, elk, mule deer and several other wild ungulate species. This new occurrence of meningeal worm on the landscape and its associated fatal effects in non-white-tailed deer ungulates is likely to lead to progressive ecological change at an ecosystem level.
Collaboration Was Key
This discovery was only possible thanks to an incredible collaborative effort involving many individuals and agencies working together, including:
- Biologists, Steven Andriashek, Dr. Troy Hegel and the Northeast Alberta Caribou Program, Alberta Fish and Wildlife Stewardship
- Owen Slater, wildlife veterinarian
- Canadian Wildlife Health Cooperative (Director Dr. Dayna Goldsmith, Associate Dr. Sawsan Ammar)
- Alberta Fish and Wildlife Officers
- Margo Pybus, provincial wildlife disease specialist, Alberta Fish and Wildlife Stewardship
- Andreanne Morency, Alberta Agriculture and Irrigation
- Animal Health Laboratory – University of Guelph
- Richard Gerhold and his laboratory team at the University of Tennessee Knoxville
Such partnerships are essential for wildlife health investigations. By pooling expertise in biology, veterinary medicine, pathology, and parasitology, we were able to confirm this finding and begin assessing its implications for caribou conservation.
What’s Next?
The Government of Alberta and CWHC will continue working together and with partners to track this parasite and share findings with wildlife managers and other stakeholders. With the support of partners, the Diagnostic Services Unit at the University of Calgary Faculty of Veterinary Medicine is working to develop an in-house PCR test that can be used to confirm future infections and reduce the cost and time of P. tenuis confirmation in the province.
How You Can Help
If you encounter sick or dead wildlife, report it to the CWHC or your local wildlife authorities. Public reporting is a vital part of early detection and response.
For more information on wildlife health and disease surveillance, visit www.cwhc.ca. Additional information about P. tenuis can be found through Alberta Fish and Wildlife: https://www.alberta.ca/wildlife-diseases-in-alberta.
Written by: Dr. Dayna Goldsmith, Director of CWHC Alberta and Owen Slater, Wildlife veterinarian