Defining parasite biodiversity at high latitudes of North America: new host and geographic records for Onchocerca cervipedis (Nematoda: Onchocercidae) in moose and caribou

Authors: VEROCAI, GUI - University Of Calgary; LEJUENE, MANIGANDAN - University Of Calgary; BECKMEN, KIMBERLEE - Alaska Department Of Fish And Game; KASHIVAKURA, CYNTIA - University Of Calgary; FUENTEALBA, CARMEN - University Of Calgary; Hoberg, Eric; KUTZ, SUSAN - University Of Calgary

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2012
Publication Date: 11/28/2012
Citation: Verocai, G., Lejuene, M., Beckmen, K., Kashivakura, C., Fuentealba, C., Hoberg, E.P., Kutz, S. 2012. Defining parasite biodiversity at high latitudes of North America: new host and geographic records for Onchocerca cervipedis (Nematoda: Onchocercidae) in moose and caribou. Parasites & Vectors. 5:242.

Interpretive Summary: The diversity and geographic distribution for parasites in ruminants across North America remains poorly defined. Resolution for these gaps in our knowledge about the occurrence of pathogens and diseases in both domestic and free-ranging ungulates results from survey activities designed to demonstrate the presence or absence of parasites. We explored the distribution of certain tissue dwelling nematodes that have historically been known to occur in cervids (particularly deer) across boreal North America. Collections and survey at high latitudes extending to near the Arctic Circle in Alaska and western Canada provided the first records of a filarial parasite, Onchocerca cerivpedis, in subspecies of moose and caribou. Our studies document a substantially greater geographic range for this parasite extending well into the SubArctic. The parasite has a complex life cycle where adult nematodes occur in tissue of the cervid host and larvae are transmitted between hosts by blood-feeding black flies. As a consequence this species and related parasites are sensitive to long term accelerated climate warming and also to extreme episodes of warming that influence the distribution of black fly vectors and developmental rates for larval parasites. These conditions are associated with (1) range expansion and host shifts among different species of cervids by parasites; and (2) amplification (increases) in parasite populations that may lead to disease and mortality. Our results and observations are of importance for disease ecologists, parasitologists and wildlife managers at the federal, state and academic sectors as it becomes increasingly necessary to understand the linkage between accelerated climate warming and its relationship to the expanding distributions for pathogens and diseases in both free-ranging wildlife species and domestic food animals.

Technical Abstract: Onchocerca cervipedis is a filarioid nematode of cervids reported from Central America to boreal regions of North America. It is found primarily in subcutaneous tissues of the legs, and is popularly known as ‘legworm’. Blackflies are intermediate hosts and transmit larvae to ungulates when they blood-feed. In this article we report the first records of O. cervipedis from high latitudes of North America and its occurrence in previously unrecognized hosts including moose (Alces americanus gigas) and caribou (Rangifer tarandus granti). Methods: We examined the subcutaneous connective tissues of the metacarpi and metatarsi of one caribou and 24 moose for parasitic lesions. Samples were collected from animals killed by subsistence hunters or animals found dead in the Northwest Territories, Canada and Alaska, USA from 2005 to 2011. Results: Subcutaneous nodules were found in ten moose from the Northwest Territories and Alaska, and one caribou from Alaska. Nematodes dissected from the lesions were identified as Onchocerca cervipedis based on morphology of female and male specimens. Histopathological findings in moose included cavitating lesions with multifocal granulomatous cellulitis containing intra-lesional microfilariae and adults, often necrotic and partially mineralized. Lesions in caribou included periosteitis with chronic cellulitis, eosinophilic and lymphoplasmacytic infiltrate and abundant granulation associated with intra-lesional adult nematodes and larvae. Sequences of the nd5 region of the mitochondrial DNA, the first generated for this species, were deposited with Genbank. Representative voucher specimens were deposited in the archives of the US National Parasite Collection. Conclusions: The geographic range of O. cervipedis is wider than previously thought, and extends into subarctic regions of Canada and Alaska. The host range is now recognized to include two additional host subspecies: the Yukon-Alaska moose and Grant’s caribou. Accelerated climate change at high latitudes may affect vector dynamics, and consequently the abundance and distribution of O. cervipedis in moose and caribou. Disease outbreaks and mortality events associated with climatic perturbations have been reported for other filarioids such as Setaria tundra in Fennoscandia, and may become an emerging issue for O. cervipedis in subarctic North America.