Understanding parasite biodiversity at high latitudes

O.cervipedis distributionStudies on parasite distribution and biodiversity are foundational to understanding how parasites may affect the health and conservation of their hosts under changing climatic conditions. At high latitudes of North America, this type of research can be logistically challenging, due to remote and vast landscapes.

The Alberta Canadian Cooperative Wildlife Health Regional Centre, together with community and government partners from the United States and the Northwest Territories, recently discovered that the range of the ‘legworm’ of cervids, Onchocerca cervipedis, is broader than previously thought. Through an ongoing community-based monitoring program in the Sahtu, and government lead disease surveillance programs in Alaska, we obtained and examined samples from caribou and moose. Using a combination of classic and molecular methods in parasitology and histopathology of tissues, and through consultation with Yukon wildlife professionals, we found that the range of O. cervipedis extends into subarctic regions of western Northwest Territories through to Alaska and as far north as, at least 66°N. Also, the Yukon-Alaska moose and the Grant’s caribou are now recognized as hosts. Prior to our study, this parasite was known from Central America to boreal regions of Canada (British Columbia and Alberta), infecting cervids and the pronghorn. These findings were published in a peer-review journal (Verocai et al. 2012, Parasites & Vectors v.5: 242).


Onchocerca is transmitted to the mammal hosts by blackflies via blood meal.  It is primarily found in subcutaneous tissues of the legs, hence its common name. In contrast to the severe disease described in black-tailed and mule deer, the parasite does not appear highly pathogenic in moose, but the effects on caribou are less certain. Subtle to severe effects in both these species may influence their susceptibility to predation. Nevertheless, climate change at high latitudes may affect the dynamics of blackflies, and consequently the abundance and distribution of the legworm in moose and caribou. Disease outbreaks and mortality events linked to climatic perturbations have been reported for related worms infecting reindeer in Northern Europe, and may become an emerging issue for O. cervipedis in subarctic North America.

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