Autumn and Winter liver fluke forecast for Northern Ireland 2014-2015

Staff at the Veterinary Sciences Division (VSD) of the Agri-Food and Biosciences Institute (AFBI), using a forecasting system based on climate data, have predicted that the overall risk of liver fluke infection during this autumn and winter in Northern Ireland will be lower than in recent years.

A lower risk is predicted because of the relatively low rainfall during June and July.

The mean monthly rainfall for May and August was higher than the Northern Ireland average with June and July having a mean monthly rainfall 25 to 30% lower than the Northern Ireland average.  Although August proved to be the wettest month of the summer, September was exceptionally dry with a rainfall of 3.55 mm compared to the Northern Ireland average of 94.5 mm. This is likely to have reduced the pasture contamination by infective larval stages of the parasite.

The mean monthly temperatures for May, June, July and September were on average 1.5°C higher than the Northern Ireland average. Daily mean temperatures of 10°C or higher are necessary for the intermediate host, the snail Galba truncatula, to breed and for the development of fluke within the snail to occur. This is also the temperature at which fluke eggs will develop and hatch. It is only when mean temperatures rise to approximately 15°C and are maintained above this level that significant multiplication of snails and fluke larval stages ensues.

Although the mean temperature for the period June to August was 14.6°C, the drier conditions during June and July would have allowed many areas to dry out. This would have reduced the ability of the intermediate host to breed and for the development of fluke within the snail to occur. However, the mild weather during the winter of 2013-14 may have allowed survival of snails and fluke eggs on the pasture, and increased the likelihood that low levels of infection might have been picked up early in the season.

In areas which are poorly drained and remain wet all year round multiplication of snails will have continued unabated due to the near ideal daily temperatures. If these areas had been grazed by infected sheep in the spring the likelihood of liver fluke infection in the autumn will remain high.

Liver fluke disease can occur in either acute or chronic forms.  The acute form occurs in sheep and is caused by the migration of large numbers of immature flukes through the liver. Acute liver fluke is often a fatal disease and has serious welfare implications. Signs 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. Flockmasters and veterinary surgeons also need to be aware of the predisposition to Black disease caused by migrating liver fluke. Cattle and sheep with access to flukey pastures should be fully vaccinated against this disease.

All farmers should review their fluke control measures at this time of year. Access to snail habitats (wet and poorly drained areas) should be reduced or sheep taken off the land and housed or moved to new clean pasture. However, in most cases, control will be based on the strategic use of anthelmintics, employing a product effective against the life cycle stages likely to be present in the flock or herd at the time of treatment. 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. At this time of year a product effective against immature and mature forms is needed. Use of such a product on out-wintered sheep once or twice in autumn and maybe in January, coupled with a treatment effective against adult flukes in early spring,  should significantly reduce the fluke burden on individual farms.

Treatment of chronic (adult) 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 the timing of housing and the effectiveness of particular anthelmintics against the fluke present on your farm. However the flukicide programme used has to be on a ‘know-your-farm’ basis and no one set of recommendations will cover all flocks or herds.

Farmers need to be aware that resistance to fluke treatments is an emerging problem and has been detected in Northern Ireland.  On some premises, products containing triclabendazole (the only flukicide currently licensed in UK and Ireland that is effective against the immature stages of liver fluke, causing acute fasciolosis in sheep) have been used almost exclusively for a number of years. On such farms it is possible that triclabendazole-containing products may now be less effective in controlling fluke infection, and for treating acutely-ill animals.  However, no other products are effective for treating acute fasciolosis, so triclabendazole should be considered for use in emergency situations in conjunction with closantel, in an attempt to partially reduce acute fluke burdens and save animals. The effectiveness of anthelmintic treatment on individual farms should be checked by taking dung samples 3-4 weeks after treatment and submitting them, through your veterinary surgeon, for laboratory examination.

In recent years, stomach (rumen) flukes have become common in sheep and cattle in NI. The intermediate snail host of these flukes deposits infective metacercaria larvae on wet pasture land. Adult rumen flukes are less damaging to sheep and cattle than liver flukes, but heavy infections of immature worms may cause diarrhoea, ill-thrift and, exceptionally, death in young animals. If you suspect that stomach fluke infection may be a problem on your farm, you should contact your veterinary surgeon to arrange for appropriate laboratory testing, and to discuss treatment options.

Remember that liver flukes, particularly in acute infections, are potentially a much more serious risk to the welfare and productivity of animals than stomach flukes. The choice of flukicides to use in autumn must reflect this. Treat first with liver fluke in mind and second for rumen fluke; if need be, use different treatments for each parasite.

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.  Please note that some fluke treatments are not suitable for use in dairy animals both while milking and whilst in calf. Given the importance of flukicides at this time of the year, it is pertinent to remind farmers of the need to avoid unacceptable residues of anthelminitics, and indeed of all veterinary medicinal compounds, in food of animal origin.  Farmers are reminded to apply the appropriate dosing and withdrawal periods, as outlined in the manufacturer’s product data sheet. Monitoring for residues takes place throughout the year.
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.

Further information on liver fluke disease in cattle and sheep may be found at www.afbini.gov.uk/adds-articles-diseases

by Hillary Edgar, Jason Barley and Bob Hanna (AFBI)
 

Notes to editors: 

AFBI carries out high quality technology research and development, statutory, analytical, and diagnostic testing functions for DARD and other Government departments, public bodies and commercial companies. 

AFBI's Vision is “Scientific excellence in Northern Ireland …  serving the world”.

All media enquiries to AFBI Press Office.

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