Liver Fluke Control in Sheep

Liver Fluke Control in Sheep

Liver fluke infestation (fasciolosis) has always been a problem during the late autumn and winter in the wetter western areas of the UK. More recently, liver fluke has been reported increasingly in eastern areas of the country due to the introduction of infested sheep.

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Causal parasite: Fasciola hepatica infects the liver in both cattle and sheep. For part of its life cycle it inhabits the snail, Limnea truncatula. This important stage of the parasite life cycle necessitates wet and warm conditions (above 7-10C) during the summer months.

·         Liver fluke causes 3 types of disease… acute, sub-acute and chronic. Essentially, late spring early/summer infestation of snails result in the autumn fluke challenge to sheep with immediate acute disease, sub-acute disease over the following weeks or chronic disease apparent three months later depending upon level of challenge.

·         Clinical presentation;

1) Acute fasciolosis: affected sheep die suddenly from haemorrhage and liver damage, with the first evidence of a problem being sudden deaths in previously healthy sheep from August to October. Inspection of others in the group reveals lethargy and reduced grazing activity. Sheep are reluctant to run caused by avoidance of pain. Sudden deaths may affect up to 10% of sheep at-risk.
Other causes of sudden death… clostridial disease, tick diseases, Pasteurellosis or septicaemic disease and louping ill.

2) Sub-acute fasciolosis: the major presenting clinical findings are rapid loss of body condition and poor fleece quality despite adequate flock nutrition. Typically, some sheep present with severe depression, inappetance, weakness and may be unable to stand. Losses typically occur from Dec onwards but may be much earlier (Oct) with severe challenge.

3) Chronic fasciolosis: the major presenting clinical findings are very poor body condition and poor fleece quality and in many sheep, bottle jaw. Affected sheep may die in an emaciated state especially when infestation is compounded by the metabolic demands of advanced pregnancy/early lactation. Loss of the ewe and her lambs can severely affect farm profits.
Poor condition affecting many of your sheep may also result from: inadequate flock nutrition, chronic parasitism including anthelmintic-resistant strains, virulent footrot, Johne’s disease, poor dentition and chronic severe lameness.

·         Diagnosis:

Acute/Sub-acute fasciolosis; based on the epidemiological data and vet blood samples which reveals raised liver enzymes. Immature flukes are demonstrated in the bile ducts and gall bladder at necropsy.

Chronic fasciolosis; is diagnosed by demonstration of fluke eggs in faecal samples. Mature flukes are demonstrated in the bile ducts and gall bladder at necropsy.

·         Treatment: Triclabendazole is highly effective at killing all stages of flukes responsible for acute fasciolosis. Drenched sheep should be moved to clean pasture or re-treated every 3 weeks for the next 3 months. Nitroxynil and Oxyclosanide are less effective against immature flukes and should only be used for treatment of sub-acute and chronic fasciolosis. Once again, treated sheep must be moved to clean pastures. Improved nutrition is essential.

·         Prevention/Control: Fluke infestations are controlled by strategic drenching based upon advice written in the flock health plan. During low risk years, triclabendazole is administered in advance of the predicted challenge during October and January, with another flukacide drug administered in May. In high risk years, flukacide drugs are given in Nov and Feb too. While eradicating the flukes from pasture may be possible, there are considerable risks from not drenching as the appearance of clinical disease in a few sheep represents serious losses in the whole flock.