In assessing the risk of liver fluke disease on any particular farm, variation between individual farms in their soil type (whether soils are heavy or free-draining) must be taken into account, in addition to weather and landform.
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 (around gates, troughs) are a particularly common location for mud snails to be found.
Aside from local conditions on the farm and prior weather conditions, it is important that livestock owners also factor in prior liver fluke history on the farm. This can be 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, and can cause 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 veterinary practitioner for diagnosis of liver fluke infection or other potential cause(s) of these clinical signs. It is recommended that carcasses be referred by a veterinary practitioner 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 to inform 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 veterinary practitioner 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, and sheep in autumn or earlier in the year if there are concerns based on 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, and sheep should also be removed 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.
Advice should always be sought on treatment protocols and 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 necessity and success of flukicide treatments.
This is especially important given that resistance to flukicides is becoming an increasing concern. In addition, bulk milk tests for antibodies to the parasite in dairy herds can be useful in monitoring year-to-year variation in exposure (please note that bulk milk tests cannot be used to judge the success of any treatment given).
Where it is feasible, and as a long-term control option, areas of fields which are suitable habitats for the intermediate host (wet muddy areas often containing clumps of rushes) should be either fenced off or drained. This will result in a permanent reduction of snail habitat.
What about Rumen Fluke?
This parasite, Calicophoron daubneyi, which shares the same intermediate host as the liver fluke, has become more prevalent in Ireland over the last number of years in both cattle and sheep. The pathogenicity of rumen fluke is mainly due to the activity of the juvenile stages in the intestine, while adult flukes in the rumen are 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, consult with your veterinary practitioner 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.