Liver fluke infections in cattle and sheep

Abstract

The trematode, Fasciola hepatica, is a cosmopolitan parasite of temperate regions that can infect a wide variety of wild and domestic mammalian species, including man. Host-responses differ amongst different species and this article focuses on the contrast between cattle and sheep, the two classes of livestock in which fasciolosis assumes the greatest economic importance. In the sheep, acute fasciolosis resulting from parenchymal damage to the liver and haemorrhage caused by migrating juvenile flukes is a severe and potentially fatal disease. In contrast, the parenchymal stages have limited effects in cattle and the acute form of the disease is extremely rare. Though there is no evidence for a functional, acquired immune response to Fasciola hepatica, cattle provide a less hospitable environment, probably due to the profound changes in parasitised bile ducts, which render them as unsuitable habitats for feeding fluke. Consequently, in untreated cattle, many liver fluke die within 18 months of infection, though some can survive for 2 years or more. In the sheep, essentially, the fluke can live as long as the sheep; up to 11 years has been reported. These differences lead to the need for different treatment approaches in cattle and sheep with respect to juvenile fluke, but do also provide some opportunities for novel control approaches, based on the relative tolerance of cattle and their ability to limit parasitic damage to the liver parenchyma.

Chronic Wasting Due to Liver and Rumen Flukes in Sheep

“…In the abomasum the enzyme pepsin weakens the cyst wall along with the enzyme trypsin in the small intestine, after which the parasite may finally emerge from the cyst. The immature fluke is now able to penetrate the gut wall and to move through the peritoneal cavity [ 16 ]. After reaching the liver and traversing its capsule, the juvenile flukes migrate through the parenchyma for up to six weeks [ 14 ].…”