Fish-carried liver trematods of Manitoba mammals
Evans, William Stuart
The commercial fisheries of Manitoba make up the fifth most important primary industry of the province. Thus it is necessary to know what parasites the freshwater fish are carrying and which of them are pathogenic to man or fish-eating animals. It has been a known fact for many years that fish harbour larval forms of helminths. The most common of these worms, parasitizing both man and animals, are the Dibothriocephalus tapeworms and the liver flukes Clonorchis sinensis and Opisthorchis felineus. The definitive host becomes infected by eating raw or under-cooked fish. However most people cook fish sufficiently, therefore cases of human infection in Manitoba are unlikely to occur. Raw fish has been and still is an important part of the diet of dogs, cats, mink, fox, and other carnivores, both wild and domestic. Fur production is Manitoba's fourth most important primary industry and many of the above mentioned carnivores are important to it... The realization that Metorchis conjunctus is present in Manitoba freshwater fish and that it has caused deaths of sledge dogs in the northern portion of the province on at least two occasions has prompted this research... Populations of liver flukes obtained experimentally showed much variation in certain characteristics used for differentiation of species of the genus Metorchis. An adequate differentiation of these species necessitated thus a thorough study of the individual variability of the morphological characters regarded by some authors as characteristic of species. This is why the present work consists of two parts. The first is the search for the secondary intermediate hosts of the opisthorchids in Manitoba, and the second, a study of the variability of the morphological characteristics used for separating the species of Metorchis.