by Paul-Emile Kajugu, Jason Barley and Bob Hanna,
AFBI Veterinary Sciences Division Disease, Surveillance & Investigations Branch
THE Agri-Food and Bio-sciences Institute (AFBI) wishes to bring to the attention of farmers the need to consider the risk of liver fluke infection in cattle and sheep this autumn and winter.
Using a forecasting system based on climate data, staff at the Institute have predicted that the overall risk of liver fluke infection during this autumn and winter will be high across Northern Ireland.
This year saw significant levels of rainfall during the summer months, higher than last year in the months of key importance, June and July, and, in general, considerably higher than in 2019.
Although in May and September rainfall was respectively 51 per cent and nine per cent less than the Northern Ireland average, from June to August rainfall was on average 64 per cent above the Northern Ireland seasonal average.
Mean monthly temperatures were lower than average in July and September (7.4 per cent and 0.1 per cent below average respectively), but were slightly above average in May, June and August (10.6 per cent, 3.5 per cent and 2.3 per cent above NI average temperature respectively). Mean temperatures of 10degC or higher are necessary both for the intermediate host to breed and for the fluke larvae to develop within the snails. A temperature of 10degC is also the minimum at which fluke eggs will develop and hatch. The mean temperature for the period May to September was 13degC.
Therefore in many areas, part-icularly those which are poorly drained and remain wet all year round, multiplication of snails will have continued unabated, and the likelihood of liver fluke infection in the autumn and winter will be particularly 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 fatal and has serious welfare implications.
Signs of severe infections include distended painful abdomen, an-aemia 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 ‘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 reduction of growth in fattening lambs and cattle. It is therefore a source of considerable financial loss to the local agricultural industry. 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.
Migrating liver fluke can also predispose animals to the clostridial infection, Black disease, and care should be taken to ensure that cattle and sheep in fluke-affected areas are 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 both immature and mature forms is needed. Use of such a product on out-wintered sheep once or twice in autumn, with possible follow up 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. 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 early 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 pro-ducts may now be less effective in controlling fluke infection, and for treating acutely-ill animals. In these circumstances, reduction of pasture contamination by eggs from chronically-infected sheep and cattle in the winter and spring is particularly important. The effectiveness of anthelmintic tr-eatment on individual farms can be checked by taking dung samples three to four weeks after treatment and submitting them, through your veterinary surgeon, for laboratory examination.
In recent years, stomach (rumen) flukes have also become common in sheep and cattle in NI, and this is particularly the case in fluke-prone areas. 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 an-imals. 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.