This is a subscriber-only article
Using a forecasting system based on climate data, staff at the Agri-Food and Biosciences Institute (AFBI) have predicted that the overall risk of liver fluke infection during this autumn and winter will be high across all areas of Northern Ireland.
This year the levels of rainfall during the months of June through to September were considerably higher than the NI average. July and September saw rainfall levels 60% above average, with June and August being 12% and 33% above average respectively.
With these conditions, the ground remained damp throughout the summer, ideal for the survival of the intermediate host, the snail Galba truncatula.
Although in May and June the mean monthly temperatures were higher than the NI average, the mean temperature for the period from July to September, at 13.2°C, was 0.5 °C lower than average.
Mean temperatures of 10°C or higher are necessary both for the breeding of the intermediate host, the snail Galba truncatula, and for the development of fluke to occur within the snail.
A temperature of 10°C is also the minimum at which fluke eggs will develop and hatch.
In areas which are poorly drained and remain wet all year round, multiplication of snails will have continued, and the likelihood of liver fluke infection in the autumn and winter is particularly high.
Forms of the disease
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, 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 ‘bottle jaw’ (swelling under the jaw).
Reduction in production
Fluke infection can cause a reduction of 5-15% 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 leave them predisposed 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.
Measures
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, 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
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.
Resistance
Farmers need to be aware that resistance to fluke treatments is an emerging problem and has been detected in NI. 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.
The effectiveness of anthelmintic treatment 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.
Rumen flukes
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 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.
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 on the AFBI website www.afbini.gov.uk.
SHARING OPTIONS: