Liver fluke (fascioliasis) is caused by the parasite Fasciola Hepatica. Disease can result from the migration of large numbers of immature flukes through the liver, or from the presence of adult flukes in the bile ducts.
The hatching of fluke eggs and the multiplication of snails depend on adequate moisture and temperatures greater than 10ºC. Such conditions usually occur from May–October in the UK although patterns have been changing in recent years. The incidence of fluke is highest in years when rainfall is above average during May–July.
Clinical signs in sheep
Three clinical forms are seen in sheep – acute, subacute and chronic fascioliasis. Which form occurs depends on the level of infection and the period over which they are ingested. Recent milder winters and wetter summers have seen changes patterns in parasite epidemiology and reported disease with earlier seasonal reports of acute disease. Signs of disease include weight loss, scouring, bottle jaw and fatalities. Each form of disease will need different treatment so speak to your veterinary surgeon for advice.
Clinical signs in cattle
Cattle are much more tolerant of infection and usually clinical signs are not seen until the animals are chronically infected. Signs are usually vague and non-specific such as reduced milk yield, poor feed conversion rate and failure to thrive. Liver fluke infection in a herd results in an extra 0.5 services per conception and increases the calving interval by 20 days. Clostridial disease is often associated with fluke as the damage done to the liver gives the ideal environment for Clostridial bacteria to thrive. Cattle are often simply found dead.
Definite diagnosis can be challenging, fluke eggs can be counted from the faeces but animals will often shed sporadically so false negatives are common. Blood tests can give an idea as to whether animals have been exposed to fluke in the past and can give a useful idea as to herd exposure.
Post Mortem exam is often the best way to get a definitive diagnosis, especially in cases of acute disease, and feedback from slaughterhouses also gives us really useful indicators of disease. Over 25% of all cattle livers are condemned because of fluke damage. Abattoirs will also often tell you if damage is historic or active which can indicate the type of treatment needed.
There are numerous treatments for fluke but you need to ensure that the correct treatment is being used for the life cycle stage you are trying to target and the time of year. Speak to your vet about the situation on your farm to work out which treatments are right for you.
All these treatments also contain a milk withdrawal period (and some cannot be used during the dry period) so routine treatment often needs to be targeted at the dry period.
There has been reports of resistance developing to Triclabendazoles (the most commonly used fluke treatment) so extra care needs to be taken to ensure it is being used effectively.
Prevention can be challenging on endemically infected farms:
- avoid grazing boggy areas of land where the snail is likely to live
- isolate any bought in stock and treat with a flukicide before they are allowed to graze to reduce contamination of the pasture
- set in place an effective flukicide treatment protocol