![]() ![]() The cercariae leave the snail and encyst on vegetation as metacercaria. The miracidium penetrates a suitable snail intermediate host (most commonly a species of the genus Lymnaea), in which a sporocyst, then rediae, then cercariae develop. In an aquatic or semi-aquatic environment, a miracidium (first larval stage) develops in each egg, which then hatches. The hermaphrodite adult flukes live in the biliary system. Fasciola hepatica infection is increasingly recognized as an important zoonosis in many parts of the world, not including Canada, with major impacts on human health. In some cases the fluke infection, especially in sheep, is complicated by the bacterium Clostridium novyi, the causative agent of "black disease" In some areas of the world where fascioliasis is endemic in ruminants, wildlife are significant reservoirs for the parasite. Acute fluke disease can be associated with notable morbidity and mortality. ![]() Sheep also develop a similar chronic disease, but more important in this host is acute fascioliasis caused by immature pre-adult flukes migrating through the liver parenchyma. In cattle disease is associated primarily with the adult flukes in the biliary system, where they cause chronic inflammation which eventually interferes with hepatic function, as well as blood loss. hepatica is a major pathogen of cattle and sheep. While some animals with this liver fluke show few if any ill effects, in many parts of the world F. Infection of the definitive host is by ingestion of this vegetation. These leave the snail and encyst as infective metacercariae on aquatic vegetation. The life cycle is indirect and requires a snail intermediate host in which the cercariae develop. Currently in Canada the parasite occurs only in cattle and is restricted to dairy cattle around Quebec City and an isolated and inexplicable focus in central Alberta. Summary The trematode Fasciola hepatica (the common liver fluke of ruminants) infects cattle and sheep, and less commonly a range of domestic and wildlife species, around the world. ![]()
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