Ireland Prepare for High Liver Fluke Levels

IRELAND, UK - Although no cases of acute liver fluke disease have yet been detected this autumn at the AFBI laboratories in Omagh and Stormont, the weather during the critical summer period of May to August was unusually wet, and therefore high levels of infection are to be expected in the late autumn. Farmers should now be on the alert for this condition.
calendar icon 12 November 2008
clock icon 4 minute read

Snail hosts for liver fluke on a muddy pasture, says Hillary Edgar and Bob Hanna, Veterinary Sciences Division Agri-Food and Biosciences Institute (AFBI). Using a forecasting system based on rainfall data, AFBI staff have predicted that the overall risk of liver fluke infection during this autumn and winter in Northern Ireland will be higher than the average in recent years, but similar to the situation last year. This year the summer rainfall was more than 50% higher than expected in Northern Ireland, and there was also severe flooding in many areas.

Calculations based on the amount and distribution of rainfall and the level of evaporation throughout May, June, July and August confirm the risk of a high incidence of acute fluke this autumn, particularly in counties Tyrone, Fermanagh and Londonderry.

Bearing in mind the extensive flooding that occurred, farmers and veterinary surgeons should be aware that the snail population may have spread to areas not usually associated with fluke. These snails may have carried fluke infection from elsewhere, or become infected from fluke eggs already present on the pasture in dung of cattle or sheep grazing earlier in the year. The metacercarial cysts, which emerge from the snails after a period of development and which are the infective stage for cattle and sheep, may therefore be present in locations where they are not usually found.

Liver fluke disease can occur in either acute or chronic forms. The acute form occurs in sheep and is caused by the passage of large numbers of immature flukes from the gut to the liver. Symptoms of severe infections include distended painful abdomen, anaemia and sudden death. In less severe cases poor production and growth, coupled with reduced appetite and abdominal pain are apparent. Chronic liver fluke disease is more common than the acute form and occurs in both sheep and cattle, usually during the winter and spring although infection can persist throughout the year. Affected animals may exhibit anaemia, ill thrift, reduced production or ‘bottle jaw’ (swelling under the jaw).

Fluke infection can cause a reduction of 5-15 per cent in the milk yield of dairy cows and loss of growth in fattening lambs and cattle. It is therefore a source of considerable unseen financial loss to the agricultural industry in Northern Ireland. Fluke infections in dairy cattle can also predispose to metabolic conditions such as ketosis and infectious diseases such as salmonellosis. The same is likely to be true for sheep.

All farmers should review their fluke control measures at this time of year.

While access to snail habitats (wet and poorly drained areas) should be reduced, the widespread contamination of land will mean that in most cases control will be based on the strategic use of anthelmintics, preferably with a product that is active against both immature and mature fluke. This is particularly important in autumn when acute fluke infection occurs in sheep and pick-up of infection by sheep and cattle is still taking place. Using such a product on out-wintered sheep on three or four occasions (once or twice in autumn, January and April) should significantly reduce the fluke burden on individual farms.

Treatment of chronic infections in cattle as well as sheep during the winter or early spring is important to help reduce pasture contamination with fluke eggs. Use of an anthelmintic with activity mainly against adult flukes may be sufficient in these circumstances, but if the recent trend of mild winters continues, out-wintered sheep will be liable to pick up acute infection much later than expected. Treatment of cattle will depend on when the timing of housing and the effectiveness of particular anthelmintics against the fluke present on your farm. The use of all currently available anthelmintics for the control of fluke in lactating dairy cows requires milk to be withheld. Treatment at drying off may therefore be more cost-effective.

Advice on the most suitable anthelmintic and other control measures can be obtained from your veterinary surgeon. The AFBI veterinary laboratories at Stormont and Omagh can assist your veterinary surgeon by testing dung and blood samples from livestock for evidence of fluke infection and associated liver damage.

Farmers also need to be aware that resistance to fluke treatments is an emerging problem. In this regard, the effectiveness of anthelmintic treatment may be checked by taking dung samples 3-4 weeks after treatment and submitting them, through your veterinary surgeon, for laboratory examination.

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