by Paul-Emile Kajugu, Jason Barley and Bob Hanna
Disease, Surveillance and Investigations Branch, Agri-Food and Biosciences Institute
THE Agri-Food and Bio-sciences Institute (AFBI) wishes to bring to the attention of farmers the need to consider a medium to high risk of liver fluke infection in sheep and cattle this autumn and winter in Northern Ireland.
Using a forecasting system based on climate data, staff at the institute have predicted that the risk of liver fluke infection during this autumn and winter will be moderate to high in the central, south and east of the Province and that high prevalence of disease is likely in the west.
In comparison to last year, the total NI rainfall in spring was lower, and the summer rainfall was significantly lower (189.4mm in 2021 compared to 398.4mm in 2020, for the months of June to August).
However, the mean summer tem-perature in 2021 was higher than that in 2020 (15.1°C and 14.0°C respectively).
The mean temperature for the period May to September 2021 was 13.7˚C compared to 13.0˚C for the same period last year.
Although the average precipitation from May to September 2021 was 4.3 per cent less than the NI rainfall average for the period, the average temperature for the same period was 6.0 per cent higher.
A mean temperature of 10˚C or higher is necessary both for the intermediate host to breed and for the fluke larvae to develop within the snails. A temperature of 10˚C is also the minimum at which fluke eggs will develop and hatch.
Since the mean temperature for the period May to September was 13.7˚C, in those areas 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 infection is often fatal and has serious welfare implications. Signs of severe infection include distended painful abdomen, anaemia and sudden death. In less severe cases, poor production and growth, coupled with reduced appetite and ab-dominal 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 known as 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 occurs across 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 likely that triclabendazole-containing prod-ucts 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.
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 rumen flukes 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.