Each year, the Department of Agriculture, Food and the Marine (DAFM) in collaboration with Met Éireann advises farmers of the predicted risk of disease caused by liver fluke (Fasciola hepatica) infection in livestock. This forecast is based on meteorological data gathered between May and October by Met Éireann.
The Disease Forecast Summary
Based on the Ollerenshaw Summer Index (Figure 1), Ulster, Connacht, north Leinster and coastal Munster are most at risk of higher losses with more moderate losses expected in south Leinster and the remainder of Munster. However, farmers in lower-risk areas should still remain vigilant for signs of disease.
Figure 1. Ollerenshaw Summer Index values 2019 and the risk of disease due to liver fluke
Other Tools for Identifying the Risk of Liver Fluke Infections
The Regional Veterinary Laboratory (RVL) Liver Fluke Abattoir ELISA Survey
Blood samples collected by DAFM staff from a selection of lambs born in 2019 (928 flocks) across 25 counties were tested for the presence of antibodies to liver fluke by the DAFM Laboratory Service to determine the level of exposure of lambs in these flocks. Data from this survey indicates that the majority of infected flocks are from counties on the western seaboard. A particularly large number of positive results were reported from flocks located in Mayo and Donegal. In these counties, exposure to liver fluke was detected in June, while animals in the southwest were apparently not exposed before August. By October, there was evidence of fluke exposure in lambs from the midlands and large parts of Leinster. Please see http://www.animalhealthsurveillance.agriculture.gov.ie/ for further details and maps of test results.
Animal Health Ireland
Preliminary data from the Animal Health Ireland Beef HealthCheck programme indicates that nationally the frequency of liver fluke detected in cattle at slaughter has remained at low levels over the summer months and into the autumn, although fluke-damaged livers were seen consistently throughout this period, particularly in cattle from north western and western counties. Trends from previous years suggest that levels of liver fluke are likely to increase over the winter months. The Beef HealthCheck programme now provides a high level of coverage of cattle nationally and work is ongoing to analyse the information it provides.
In order to assess the risk of liver fluke disease on any particular farm, various environmental factors, particularly climate, landform and soil type (whether soils are heavy or free-draining) must be taken into account. This is because the intermediate host of the parasite which is a mud snail (Galba truncatula), tends to be located in soil that is slightly acidic and muddy. Thus, areas of fields with rushes or wet patches (e.g. around gates, troughs) are particularly important with regard to liver fluke risk. In addition, livestock owners should also factor in prior liver fluke history on the farm as this is an important indicator of future disease risks.
Monitoring of Disease
Liver fluke infection tends to be chronic in cattle, resulting in ill-thrift and poor performance. In sheep, chronic disease can occur but infection may also result in more acute clinical signs, causing sudden death in cases of heavy challenge.
Livestock owners should continue to be vigilant for any signs of illness or ill-thrift in their animals and should consult with their private veterinary practitioner (PVP) if they are concerned about liver fluke infection or other potential cause(s) of these clinical signs. It is recommended that carcasses be referred by a PVP to an RVL for necropsy in cases where the cause of death is not obvious.
Information from abattoir examination of livers of previously sold fattened stock is also a valuable source of information for livestock owners of the prevalence of liver fluke infection on their own farm or on the efficacy of their control programme.
Treatment and Control
In areas of high risk and on farms where liver fluke infection has been diagnosed or where there is a prior history, livestock owners should consult with their PVP to devise an appropriate treatment and control programme.
When using flukicides to control and treat liver fluke infection, particular attention should be given to dosing cattle at the time of housing or shortly thereafter, and sheep in autumn or earlier in the year where indicated by faecal examination results or prior disease history. For sheep, a drug effective against early immature as well as late immature and mature flukes should be used to protect against acute disease. In addition, sheep should be moved from affected pasture to prevent re-infection. If the flukicide given to cattle at housing is not effective against early immature fluke, then faecal samples should be taken six to eight weeks after housing and tested for the presence of liver fluke eggs. This will determine whether a follow-up flukicide treatment is necessary.
Given that flukicides do not have a persistent activity, any cattle or sheep that are out-wintered are at risk of further infection post-treatment and follow-up flukicide treatments may be necessary. This is especially so if they remain on high-risk pastures and it is advised to always monitor livestock for the occurrence of re-infection.
Advice should always be sought on treatment protocols and on the appropriate interval at which such treatments should be given. Testing faecal samples for the presence of liver fluke eggs can help determine both the need and success of flukicide treatments. This is especially important given that resistance to flukicides is becoming an increasing concern. In addition, bulk milk testing for antibodies can be used in dairy herds to monitor year-to-year variation in exposure (please note that bulk milk tests cannot be used to judge the success of any treatment given).
Where feasible, and as a long-term control option, areas of farms that provide suitable habitat for the mud snail such as wet muddy areas should be either fenced off or drained. This will result in a permanent reduction of snail habitat.
What about Rumen Fluke?
The rumen fluke, Calicophoron daubneyi, which has become more prevalent in Ireland over the last number of years in both cattle and sheep, infects the same intermediate host as the liver fluke. The pathogenicity of rumen fluke is mainly due to the activity of the juvenile stages in the intestine, while the presence of adult flukes in the rumen is not normally associated with clinical signs.
If clinical signs such as rapid weight loss or diarrhoea are seen, or if there is a history of previous disease from rumen fluke on the farm, livestock owners should consult with their PVP as to whether treatment for rumen fluke is required. The finding of rumen fluke eggs in faecal samples of animals that are thriving and producing well does not indicate that treatment for rumen fluke is necessary.
Further Information Sources
Further details on liver fluke and its control and information on flukicide selection for cattle along with information on the Beef Health Check programme are available at http://animalhealthireland.ie/?page_id=405.
Information on the names and specifications of flukicides licensed for sheep may be accessed at https://www.teagasc.ie/media/website/publications/2018/Products-licensed-for-control-of-parasites-in-sheep.pdf.