A parasite of the North American river otter: Potential cause of blindness in burbot?
The North American river otter (Lontra canadensis) is a fur bearing mammal of economic value. Historically they were distributed throughout Canada and United States but their present range is fragmented due to pollution and urbanization. Reintroduction efforts have greatly expanded the distribution of this mammal in the United States and Canada. In spite of these efforts, the North American river otter is considered vulnerable across much of its range. Therefore, it is important to study the diseases and the disease causing agents that this animal is susceptible to. Nonetheless, there have been relatively few studies on parasitic fauna of river otters.
As part of a 6 week wildlife parasitology internship at the Alberta-CWHC, Baptiste Froidefond, a second year DVM student from École Nationale Vétérinaire, Toulouse, France investigated gastro-intestinal parasites of North American river otters (supervised by Dr. Mani Lejeune). Baptiste found the tiny trematode parasite, Enhydridiplostomum alarioides in some of the otters. This parasite belongs to the subfamily: Diplostomatinae (Parasites of birds). The members of this subfamily generally use birds as definitive hosts and aquatic snails as intermediate hosts. The parasitic stages (cercaria) released from the snails encyst (metacercaria) on the eyes of surface and bottom dwelling fresh water fishes and can cause blindness. The life cycle is completed when the definitive hosts feed on the infected, blinded fish.
The specific life cycle for E. alarioides is unknown; however, it is possible that it is transmitted to river otters through burbot or other food fish. A previous Healthy Wildlife blog post reported that 35% of burbot had cataracts associated with parasitic stages (metacercaria) belonging to genus Diplostomum. However it should be noted that parasite species confirmation based only on morphology of metacercaria is difficult and one has to resort to molecular methods for accurate identification. Moreover, burbot are bottom dwellers, and the likelihood of them being fed on by birds is low. These fish are therefore considered to be ‘ecological sinks’ for the parasites if they require bird hosts. Given that E.alarioides appears to be fairly common in river otters, and that burbot are a preferred food source, further DNA-based studies are needed to determine if E.alarioides has a life cycle that includes the predator-prey association between river otter and burbot.
Acknowledgement: Fur Institute of Canada, Vegreville, Alberta for allowing secondary use of tissues collected on necropsy of North American river otter trap assessment project
Submitted by Manigandan Lejeune, CWHC Alberta