Focus - December 2020
Fluke forecast from Department of Agriculture, Food and the Marine
Each year, the Department of Agriculture, Food and the Marine (DAFM), in collaboration with Met Éireann, predicts the risk of disease caused by Fasciola hepatica/liver fluke infection in livestock. This year’s forecast is based on meteorological data gathered between May and October 2020 by Met Éireann. This report is published here, in full, as a useful resource for all large-animal veterinary professionals
After an initially drier start in May, the monthly index values for June to September show widespread maximum values due to the wet conditions that occurred. This has resulted in rather high values nationwide which range from 403 to 484 (see Figure 1). This indicates a widespread prevalence of the disease.
Identifying the risk and timing of infections
The regional veterinary laboratory (RVL) Liver Fluke Abattoir ELISA Survey
Blood samples collected by DAFM staff from a selection of lambs born in 2020 (n=478 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. Some positive and inconclusive results were found in counties outside of the west and northwest in the August testing, possibly associated with a high summer rainfall level. By October, as well as a lot of positive and inconclusive results in counties on the western seaboard, there was substantial evidence of fluke exposure in lambs from the border areas, midlands and other parts of Leinster.
See www.animalhealthsurveillance.agriculture.gov.ie/ for further details and maps of test results.
Animal Health Ireland
The Beef HealthCheck programme, run in partnership with Meat Industry Ireland, collects and reports liver fluke information in cattle at slaughter from participating factories. In 2020 (to date, 18-11-2020) an average of 51% of herds showed at least one animal with liver damage due to liver fluke at slaughter and live liver fluke parasites were seen in 14% of herds. This year’s levels of liver fluke challenge are very similar to those reported in 2019 but in the second half of this year, live liver fluke detections were higher than those seen last year. It is important for farmers to know whether liver fluke is present on the farm and to treat accordingly to avoid production losses.
The Beef HealthCheck reports are available on the Irish Cattle and Beef Federation (ICBF) website. Visit
http://animalhealthireland.ie for further details on how to access this information.
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 (eg. around gates, troughs) are particularly important in relation 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.
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 must 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 carcases be referred by a PVP to an RVL for post-mortem examination/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.
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 liver fluke antibodies may be useful in dairy herds to monitor variation in exposure.
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.
Figure 1: Ollerenshaw Summer Index values 2020 and the risk of disease due to liver fluke