Symptoms & Treatment of Liver Fluke

Given the wet conditions during the first half of the summer there is a high risk of liver fluke this autumn. Liver fluke infection is caused by the parasite Fasciola hepatica; it lives in the bile ducts of a ruminant's liver. The disease affects both cattle and sheep and is estimated to cost the cattle industry £23 million annually.

The fluke life cycle involves a water snail as an intermediate host. This snail relies on there being sufficient moisture and an adequate temperature (above 7 - 10oC) during the summer to survive and breed, dictating the risk of your animals being affected by the fluke. Therefore, a warm, wet summer like we've had so far will be ideal!

The fluke eggs are passed in the cow or sheep's dung. They then develop through 5 larval stages, including two through the water snails. The penultimate stage is released from the snail between August - October and form into the infective metacercariae. These can survive on pasture for several months where they are then picked up from the grass as the animal grazes. Once inside the animal the metacercariae develop into immature fluke; these migrate to the liver reaching the bile ducts where they develop into adult fluke.

Disease is seen from late autumn onwards. There are three different clinical presentations of fluke infestation (fasciolosis):

Acute Fasciolosis

Affecting sheep, the acute infection causes sudden death in previously healthy sheep from August - October. This is caused by haemorrhage and liver damage as the immature fluke migrate to the bile ducts. Inspection of other animals in the flock will reveal depressed animals with poor grazing activity and lethargy due to pain. Sudden deaths from acute fluke can affect up to 10% of a group at one time.

Subacute Fasciolosis

Again, usually only affecting sheep, these animals usually present with rapid weight loss and poor fleece quality. As with the acute disease, some animals will be depressed, lethargic and reluctant to graze. Deaths typically occur from November onwards.

Chronic Fasciolosis

Seen in both cattle and sheep, this presentation is normally characterised by slow but excessive weight loss, with or without diarrhoea. Production is also affected, with dairy cows giving a reduced milk yield (loss of up to 1kg/day) and having poor fertility (increasing calving interval by 20 days). Infection of spring calving beef cows and pregnant ewes can be particularly severe as the fluke exacerbates the metabolic demands of advanced pregnancy. This can result in the birth of weak calves and lambs from dams with little milk and resulting high perinatal deaths. Weight gain in growing cattle can also be depressed by up to 1.2kg/week.

Diagnosis of acute and subacute fluke infestation is best performed through post mortem of any animals that die, to rule out other causes of sudden death. If that is not possible, bloods can be taken from depressed animals in the group to assess disease exposure and liver damage.

Chronic fluke is can be diagnosed by the clinical signs and history. This can then be confirmed by blood, faecal or milk samples. In milking herds a routine bulk milk sample can be taken to monitor the percentage of infection within your herd.

Treatment is by using a flukicide product, not just a normal wormer. There are many products available - some of which only treat adult fluke and not the migrating immature parasites and some which treat both fluke and worms.

Sheep with acute fasciolosis need to be treated with a product that kills immature fluke. The best option is Triclabendazole (e.g. Fasinex, Tribex) as it kills immature fluke from 2 days old through to adult fluke. However, there is increasing resistance to this product so its use should be avoided if possible.

Nitroxynil (Trodax 34%), Closantel (Closamectin) and Clorsulon (Ivomec Super,Virbamec Super) only treat adult flukes so should be used for chronic fasciolosis. Clorsulon and Closantel are usually in products alongside ivermectin so can be used for treating worms as well so their use should be taken into account with your worming regimes.

A typical annual fluke treatment protocol in a low risk area would be as follows:
- October           Trodax         To kill adult fluke at housing
- January           Trodax         To kill any further adults developed during winter

A typical annual fluke treatment protocol in a high risk area would be as follows:
- Housing            Fasinex      To kill all fluke at housing/wintering
- January            Trodax        To kill any further adults developed during winter
- May                  Trodax        To kill any overwintered fluke
- September       Fasinex      To kill developing fluke if indicated from clinical signs

The recovery of animals from fluke can often be slow depending on the damage to the liver, to help recovery their feed ration should be increased to allow weight gain. Once treated, animals should be moved to pastures clean of fluke (again, this should also depend on your worming regime - discuss this with one of us if concerned).

Any animals introduced to the farm should be treated with Triclabendazole as part of their quarantine protocol.

Any fluke control programme should include prevention if possible to reduce the potential parasitic load, including removal of snail habitats from the cattle or sheep's grazing area. This could be achieved by draining wet areas or fencing off areas of standing water.

1st October 2012

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