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Natural and Experimental Ophidiomycosis

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Title: Natural and Experimental Ophidiomycosis
Author: McKenzie, Christina
Department: Department of Pathobiology
Program: Pathobiology
Advisor: Jardine, ClaireNemeth, Nicole
Abstract: Ophidiomycosis (snake fungal disease) is caused by the fungus Ophidiomyces ophiodiicola and is the most common cause of skin lesions in snakes in North America. Reports of this disease in the wild have been increasing over the past 10 years, including in Ontario. To better understand this disease, we examined naturally infected snakes (nine carcasses, 12 biopsies) submitted to the Canadian Wildlife Health Cooperative-Ontario/Nunavut node in 2012-2018. Affected species included the eastern foxsnake (Pantherophis vulpinus; n = 15), gray ratsnake (Pantherophis spiloides; n = 3), eastern massasauga (Sistrurus catenatus; n = 2) and queensnake (Regina septemvittata; n = 1). Lesion severity varied from incidental microscopic skin lesions to fatal, necrotizing, and ulcerative facial lesions. Although the dermal lesions of ophidiomycosis in free-ranging snakes are well described in numerous species, there are many knowledge gaps in our understanding of transmission, pathogenesis, morbidity and mortality, and the effects of brumation and temperature on disease development. We sought to fill some of these gaps by developing an experimental model using subcutaneous injection of O. ophiodiicola conidia in juvenile red cornsnakes (Patherophis guttatus). We then co-housed inoculated and non-inoculated snakes during brumation. Every inoculated snake developed gross and/or microscopic ophidiomycosis lesions. These consisted primarily of heterophilic and granulomatous inflammation with intralesional fungal hyphae in the dermis, subcutaneous tissue, and muscle. We also observed embolic fungal granulomas in 21/23 (91 %) inoculated snakes throughout the liver and within the coelomic connective tissue. Quantitative PCR for O. ophiodiicola was positive for 21 % of skin swabs, 37 % of exuvia and 100 % of liver samples for inoculated snakes. A single post brumation skin swab from a co-housed, non-inoculated snake tested positive using quantitative polymerase chain reaction. This snake had microscopic lesions consistent with ophidiomycosis, suggestive of horizontal transmission. Over the 70-day experiment, 87 % of inoculated snakes died of ophidiomycosis. No control snakes developed ophidiomycosis lesions or tested qPCR positive. Overall, our description of ophidiomycosis in Canadian free-ranging snakes combined with the knowledge gained from our experimental work offers insight into the pathogenesis and ecology of this important disease of free-ranging snakes in North America.
Date: 2020-08
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Embargoed Until: 2021-08-21

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