Rose Young, BVM BVS MRCVS
Recent estimates suggest fluke costs the industry £20 million annually; approximately £3-£5 per affected ewe and £30-£200 per beef animal (AHDB data) with approximately 20% of cattle livers and 5% of sheep livers condemned at slaughter due to fluke.
Live fluke life cycle
Fasciola Hepatica, or ‘Liver Fluke’ is an internal parasite affecting primarily the liver and bile system of a wide variety of mammals. Symptoms can vary from production loss to sudden death, depending on season, species, duration and level of infection. Weather conditions play a major role in fluke risk; the NADIS forecast (www.nadis.org.uk/parasite-forecast.aspx) makes monthly predictions about the likely parasite populations in different areas of the country, based on rainfall and temperatures.
As temperatures rise in spring, fluke start hatching and looking for snails to inhabit; they spend five to twelve weeks inside the snail, after which point the pasture starts to become contaminated with infectious cysts.
Acute form (approximately May-Sept)
After ingestion by the animal, larvae hatch in the intestine and travel through the abdomen to their final destination, the liver and bile ducts. After around four weeks, larvae are
large enough to cause tissue damage; if large numbers of larvae migrate over a short period, this damage can be severe, causing:
• Blood loss, leading to anaemia and pale membranes
• Dull, weak, inappetant
• Abdominal pain
• Sudden death and ‘Blacks Disease’ (sheep)
Chronic form (approximately July-March)
Ingested flukes take a number of weeks to reach maturity inside the animal. After the initial risk period for acute disease, fluke spend a further six-eight weeks inside the liver before they reach maturity and are able to produce eggs. The adult fluke can survive inside the animal for considerable periods of time (up to two years), which results in protein loss from the blood and scarring to the liver tissue causing:
• Production loss
• Weight loss and ill-thrift
• Bottle jaw
• In some cases diarrhoea (cattle)
It is advisable to monitor the presence and levels of fluke in a herd or flock, look at abattoir reports, assess local risk factors such as climate and geography, and treat strategically during
the year to prevent problems developing.
• Faecal fluke egg sampling
• Faecal fluke coproantigen – suitable for individual cases
• Blood/bulk milk fluke antibody
• Abattoir feedback
Different treatments or ‘flukicides’ act on different life stages of fluke, so when and how often to treat groups will depend on the season and likely pathogen load. Treatment of dairy cattle is also somewhat complicated, since some products are not permitted for use in animals producing milk for human consumption. This would also apply to sheep or goats producing milk for human consumption where additional withhold rules apply.