Widespread geographic distribution of filarioid nematodes in caribou (Rangifer tarandus sspp.) in Canada

The caribou (<i>Rangifer tarandus</i> sspp.) is a keystone wildlife species in northern ecosystems that plays a central role in the culture, spirituality and food security of Indigenous People. The Arctic is currently experiencing an unprecedented rate of climate change, including warming temperatures and altered patterns of precipitation. These environmental changes can facilitate the transmission of arthropod-borne parasites, such as filarioid nematodes. Filarioids are an important cause of morbidity and occasional mortality in <i>Rangifer</i> in Fennoscandia, however, much of the ecology and epidemiology of these parasites in caribou in North America, including Canada, remains unknown. We aimed to determine the parasitic diversity and geographic distribution of filarioid nematodes in three Canadian designatable units (DU) of caribou (barren-ground, boreal and Dolphin & Union) from Northwest Territories, Nunavut and Newfoundland & Labrador. Genomic DNA extracted from 768 blood samples was screened for filarioid nematodes using real-time PCR. The positive samples were Sanger sequenced to identify the parasite present. Based on the sequencing results, we identified <i>Setaria yehi</i> and <i>Onchocerca cervipedis</i> s.l. We then standardized a TaqMan probe based duplex droplet digital PCR (ddPCR) protocol for the simultaneous detection of <i>S. yehi</i> and <i>O. cervipedis</i> s.l. Based on real-time PCR results, 8/768 samples were positive. <i>Setaria yehi</i> and <i>O. cervipedis</i> s.l. were present in 4 separate samples (0.5%) each. Using ddPCR, 68/192 samples were positive (35.4%). <i>Setaria yehi</i> DNA was detected in 57/192 positive samples (29.7%), <i>O</i>. <i>cervipedis</i> s.l. DNA was present in 22/192 samples (11.5%) and 11/192 samples (5.7%) had co-infections. <i>Setaria yehi</i> was detected in all three DUs tested. <i>Onchocerca cervipedis</i> s.l. were found in barren-ground and boreal caribou, but not from the Dolphin and Union caribou. Through this broad-based survey and through developing and implementing advanced molecular methodologies, we have documented the apparent distribution and diversity of <i>S. yehi</i> and <i>O. cervipedis</i> s.l. in parts of three Canadian DUs of caribou. The knowledge gained from this study provides baseline data and methodology for the further elucidation of the epidemiology of these parasites in North America.