Morphological and morphometric differentiation of dorsal-spined first stage larvae of lungworms, (Nematoda: Protostrongylidae) infecting muskoxen (Ovibos moschatus) in the Central Canadian Arctic

Authors: KAFLE, PRATAP - University Of Calgary; LEJEUNE, MANDIGAN - University Of Calgary; VEROCAI, GUILHERME - University Of Calgary; Hoberg, Eric; KUTZ, SUSAN - University Of Calgary

Submitted to: International Journal for Parasitology: Parasites and Wildlife
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2015
Publication Date: 6/10/2015
Citation: Kafle, P., Lejeune, M., Verocai, G., Hoberg, E.P., Kutz, S.J. 2015. Morphological and morphometric differentiation of dorsal-spined first stage larvae of lungworms, (Nematoda: Protostrongylidae) infecting muskoxen (Ovibos moschatus) in the Central Canadian Arctic. International Journal for Parasitology: Parasites and Wildlife. 4(3):283-290.

Interpretive Summary: Lungworm parasites in ungulates respond to accelerated climate warming and environmental disruption, with changes in host and geographic distribution contributing to disease outbreaks in free-ranging and domestic host species. Umingmakstrongylus pallikuukensis and Varestrongylus eleguneniensis are the two most common protostrongylid nematodes infecting muskoxen in the North American Arctic and Subarctic. First stage larvae (L1) of both these lungworms have a characteristic dorsal spine originating at the level of proximal fold of the tail extension, and considerable morphological similarity that makes their differential diagnosis very difficult. Accurate identification of these and related parasites is of critical importance as a basic foundation to recognize changing patterns of distribution in space and time. Using light microscopy, we studied in detail and identified the key differences in morphological and morphometric features of L1 of these two species and evaluated these features for larval identification; limited comparisons to a third species, Cystocaulus ocreatus, the putative sister of Uminmgakstrongylus were also considered. Species identities were confirmed based on the ITS-2 region of the nuclear ribosomal DNA. We documented key differentiating features and developed a laboratory guide for L1 unequivocal identification that was successfully applied by experienced scientists and those with minimal training. The main utility of our protocols is in rapid and accurate monitoring of rapidly changing distributions and range expansion for these parasites in the subarctic and Arctic. This type of study enabling species-level parasite identification is also critical for defining biodiversity, detecting mixed infections, and understanding host-parasite interactions. Morphological identification is a simple, reliable and cost-effective alternative to labor and equipment intensive molecular methods and can easily be performed in low resource settings. These comparative methods can have broad utility among parasitologists, disease ecologists, and wildlife and conservation biologists in laboratories across the government and academic sectors, and among NGO's with interests in biodiversity, climate and animal disease.

Technical Abstract: Umingmakstrongylus pallikuukensis and Varestrongylus eleguneniensis are the two most common protostrongylid nematodes infecting muskoxen in the North American Arctic and Subarctic. First stage larvae (L1) of both these lungworms have a characteristic dorsal spine originating at the level of proximal fold of the tail extension, and high morphological similarity that makes their differential diagnosis very difficult. Using light microscopy, we studied in detail and identified the key differences in morphological and morphometric features of L1 of these two species and evaluated these features for larval identification; limited comparisons to Cystocaulus ocreatus, the putative sister of Uminmgakstrongylus were also considered. Thirty L1 of each species from naturally infected muskoxen were studied in to identify morphological and morphometric features on which they could be differentiated. Species identities were confirmed based on the ITS-2 region of the nuclear ribosomal DNA. Key differentiating features include: length and morphology of the tail extension, curvature of the body of heat fixed larvae, ventral post-anal transverse cuticular striations, and total body length. A lab guide for L1 differentiation based on these species-specific characters was prepared and used by an experienced observer to identify an additional 35 L1 extracted from a different set of fecal samples from free-ranging muskoxen with mixed infections. The identities of these L1 were confirmed by sequencing of the ITS-2 region. Accuracy of morphological identification was 100 percent, reflecting the reliability of the proposed guide for differentiation. Using the guide, three minimally trained lab assistants fixed and accurately identified 10 of 10 L1 each. The main utility of this study is to monitor the overlapping range expansion of both parasites in the Canadian Arctic. This type of study enabling species-level parasite identification is also critical for defining biodiversity, detecting mixed infections, and understanding host-parasite interactions. Morphological identification is a simple, reliable and cost-effective alternative to labor and equipment intensive molecular methods and can easily be performed in low resource settings.