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Vet's view.

Byline: Iain Carrington

AFTER a wet summer and movement restrictions, it's important to consider a likely rise in liver fluke disease.

In Britain, fascioliasis disease is caused mainly by a trematode parasite called fasciola hepatica. It can lead to two disease conditions, an acute and a chronic form.

Eggs are passed into the faeces of chronically infected animals. These only hatch in a moist environment when the temperature exceeds 10C.

This process normally takes up to four weeks producing an intermediate stage called miracidia which must infect a particular type of snail within three hours. The mud snail called lymnaea truncatula, is found in boggy areas with neutral or alkaline soil conditions. The parasite then undergoes multiplication in the snail for two to four months depending on the temperature, although snails can carry the parasite over winter.

The infective stage is usually released on to the pasture between August and October, when it forms cysts on plants which can survive for several months. Over-wintering of the infection in the host allows infection to occur in April or May.

Acute fascioliasis is seen more in sheep about six weeks after ingestion of cysts over a short period.

Once in the small intestine, the parasite penetrates the gut wall, entering the abdomen where it migrates to the liver. There are often as many as 1,000 immature fluke burrowing through the liver. This causes massive damage and symptoms including weakness, anaemia, abdominal pain and swelling of the abdomen with fluid. Mortality is high, and the animal may die. At this time, no eggs are present in the faeces, as the fluke must first reach the bile ducts before maturing into adults about 10 to 12 weeks after ingestion.

Chronic fascioliasis is seen when the adult flukes are in the bile ducts sucking blood. The liver is damaged by the flukes, and the scar tissue makes the organ hard and fibrous. This is a slow disease with diarrhoea, anaemia and often 'bottle jaw' (a soft fluid swelling under the jaw).

It causes problems in slaughter animals as the livers are condemned. There is also a reduction in carcase weight and a loss in value. If you sell livestock direct to slaughter, find out from the abattoir if they have found evidence of the condition at slaughter.

With liver fluke, limit access to the intermediate host or its habitat. Deal with the boggy areas of ground where snails live, by fencing them off from livestock, or improve drainage if small areas are affected. For larger areas, molluscicides have been used to kill snails, but environmental considerations may make this method unacceptable.

Screening faecal samples for worm and fluke eggs is useful, but a negative result is not always what it seems.

Treatment involves a yearly 'dose' in the autumn in less badly affected areas, but where the problem is severe, a 'dose' in late spring is recommended.

Compounds can come either as a drench or an injection. So far, a pour on has not been available. It is important to check the active ingredient of the product you choose.

Combination fluke and wormers are available, but it is useful to seek advice. Generally, all will remove more than 90% of adult fluke, but results against the immature stages varies. The most effective is triclabendazole which kills fluke a few days after ingestion. Closantel and nitroxynil are effective too, and at normal dose rates will give a good kill from about the six-week stage. Others will only kill adult fluke in the bile duct.

It is also of great importance to ensure the dose given is adequate for the animal's weight, as the wrong dosage leads to resistance.

Iain Carrington is with Intake Vets, Hexham.
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Title Annotation:Business
Publication:The Journal (Newcastle, England)
Date:Oct 6, 2007
Words:620
Previous Article:Focusing on improvement; farming.
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