Liver fluke or fasciolosis is the disease caused by Fasciola hepatica, a trematode or flat worm.
Fluke can occur in a variety of animals and can even be zoonotic and cause disease in man.
Fluke infection is estimated to cost the UK agriculture industry about £300 million a year. Liver condemnations alone cost £3.2 million in 2010.
How is the disease transmitted and spread?
Liver damage occurs when the juvenile (immature) fluke migrate through the liver of the animal. This results in scaring of the liver tissue which can be seen at the abattoir or post mortem. This migration through the liver is just one part of a complicated life cycle involving stages outside the animal as well as inside the animal. Severity of disease depends on the number of parasites that infect the animal.
What are the clinical signs?
Cattle typically develop chronic disease and classically show loss of weight, condition and become anaemic. Sometimes cattle develop diarrhoea, but whether this is a direct consequence of fluke infection or due to other reasons, such as co-infection with Salmonella Dublin is not clear.
Animals become infected after ingesting the infective stage (known as metacercaria), which contaminates grass and other vegetation. These hatch in the small intestine and migrate across the gut wall and directly into the liver. The juvenile flukes migrate through the liver tissue, feeding and growing until they reach the bile ducts. The migrating flukes cause liver damage, destruction of tissue and haemorrhage. In sheep, this causes acute disease and commonly the death of animals, but acute disease is seen rarely in cattle in the UK.
Evidence from various sources suggests that the prevalence of infection has increased considerably in recent years for a variety of reasons including:
- changing climate
- changing farming practices
- increased animal movements.
Prevention & control of the disease
There are growing concerns about anthelmintic resistance, particularly to triclabendazole.
Fluke has also been shown to modulate the host’s immune system; this affects diagnosis and susceptibility to other infectious agents, including bovine tuberculosis.
Control of fluke in cattle requires a thorough understanding of the biology of the parasite, its life cycle and epidemiology and the control options available for each individual farm.
An industry wide project know as Sustainable worm control strategies for cattle has made available a techincal guide for veterinary practitioners and advisors on aspects of liver fluke control along with ten key actions to management cattle to minimise risk of infection.