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

Guilherme G Verocai1*, Manigandan Lejeune2, Kimberlee B Beckmen3, Cyntia K Kashivakura1, Alasdair M Veitch4, Richard A Popko4, Carmen Fuentealba15, Eric P Hoberg6 and Susan J Kutz12

Author Affiliations

1 Department of Ecosystem and Public Health, Faculty of Veterinary Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada

2 Canadian Cooperative Wildlife Health Centre, Calgary AB Canada, Faculty of Veterinary Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada

3 Division of Wildlife Conservation, Alaska Department of Fish and Game, 1300 College Road, Fairbanks, AK, 99701, USA

4 Department of Environment and Natural Resources, Government of the Northwest Territories, Norman Wells, NT, Canada

5 Present address: Department of Structure and Function, School of Veterinary Medicine, Ross University, Basseterre, St. Kitts, St. Kitts and Nevis

6 US National Parasite Collection, Agricultural Research Service, USDA, BARC East No. 1180, 10300 Baltimore Avenue, Beltsville, MD, 20705, USA

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Parasites & Vectors 2012, 5:242  doi:10.1186/1756-3305-5-242

Published: 30 October 2012



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 more commonly 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 host subspecies including the Yukon-Alaska moose (Alces americanus gigas) and the Grant’s caribou (Rangifer tarandus granti).


We examined the subcutaneous connective tissues of the metacarpi and/or metatarsi of 34 moose and one caribou for parasitic lesions. Samples were collected from animals killed by subsistence hunters or animals found dead in the Northwest Territories (NT), Canada and Alaska (AK), USA from 2005 to 2012. Genomic DNA lysate was prepared from nematode fragments collected from two moose. The nd5 region of the mitochondrial DNA was amplified by PCR and sequenced.


Subcutaneous nodules were found in 12 moose from the NT and AK, and one caribou from AK. 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 intralesional microfilariae and adults, often necrotic and partially mineralized. Lesions in the caribou included periosteitis with chronic cellulitis, eosinophilic and lymphoplasmacytic infiltrate, and abundant granulation associated with intralesional adult nematodes and larvae. Sequences of the nd5 region (471bp), the first generated for this species, were deposited with Genbank (JN580791 and JN580792). Representative voucher specimens were deposited in the archives of the United States National Parasite Collection.


The geographic range of O. cervipedis is broader than previously thought, and extends into subarctic regions of western North America, at least to latitude 66°N. The host range is now recognized to include two additional 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.

Alces; Caribou; Legworm; North America; Onchocerca cervipedis; Moose; Rangifer; Subarctic; Vector-borne diseases