Helminth Parasites of Wisconsin Muskrats and Literature Review of North American Muskrat Parasites and Zoonotic Diseases

Abstract

This paper seeks to develop a comprehensive review of internal helminth parasites and zoonotic diseases of muskrats in the United States in addition to a survey of current internal helminth parasites of muskrat trapped in Wisconsin. Zoonotic diseases in muskrats are of concern primarily because of the high risk of transmission to recreational trappers. Although few zoonotic diseases are of real concern, the presence of Leptospira spp., Pasteurella spp., and Francisella tularensis, the causative agents of leptospirosis, pasteurellosis, and tularemia respectively, in North American muskrats are risk factors for those that may encounter muskrats or frequent areas where they are common. The community of parasites infecting muskrats has been well-studied throughout North America and their new range as invaders in Europe and Asia. However, the specific community of parasites in Wisconsin muskrats has not been recently studied. External parasites are rare in muskrats, because of their semi-aquatic lifestyle, but small mites are relatively common. Digenean trematode parasites are most diverse in muskrats, followed by nematodes, cestodes, protists, and acanthocephalans. The most common trematodes include Alaria mustelae, Echinostoma spp., Notocotylus urbanensis, Quinquiserialis quinqueserialis, and Wardius zibethicus. The most common nematodes are Capillaria hepatica, C. michiganensis, and Strongyloides ratti. The most common cestodes are Hymenolepis spp. and Taenia taeniaeformis. In this survey of parasites from Wisconsin muskrats, 49 muskrats were trapped from three locations during the 2010 and 2011 trapping seasons. Carcasses were frozen until dissection. After thawing, internal organs were removed for examination for parasites and cysts under a dissecting microscope. The contents of the intestinal tract were washed through three consecutively smaller sieves, the smallest with a mesh diameter of 500 μm. Any parasites found were preserved in AFA and/or 70% ethanol and kept in vials for identification. Only six helminth parasite species were discovered from the muskrats examined. Echinostoma sp. and Quinqueserialis quinqueserialis were very common and found in high abundances in those infected. Notocotylus urbanensis was isolated from two muskrats, and Hymenolepis sp., Taenia taeniaeformis, and an unidentified trichostrongyloid nematode were each isolated from single muskrat hosts. Analysis was employed to discover any significant differences between the descriptive host variables and parasite infection prevalence (i.e., the % of hosts infected with a parasite species) and intensity (i.e., the number of individual parasites of a particular species in a host). The descriptive variables were location or site of capture, mass/length ratio, sex, and maturity (i.e., juvenile or adult). These variables were tested against overall parasite intensity, Echinostoma sp. prevalence and intensity, and Quinqueserialis quinqueserialis prevalence and intensity. While there was quite a bit of variation between locations and individual muskrats, only two significant effects were discovered: a negative relationship between the maturity of the muskrat and overall parasite intensity and a similar link between maturity of the muskrat and Echinostoma sp. intensity. Both of these tests found juveniles more heavily parasitized than adults.