What are mud snails?
The mud snail (Galba truncatula) is small in size at 7-12mm, but large and increasing in population. Prolific in undrained waters like marshes, streams and ditches, but also very much at home in boggy gateways and around feed and water troughs it is the intermediate host of parasitic fluke, Fasciola hepatica. Just one fluke egg hatching to a miracidium on pasture infecting the snail can produce 600 infective metacercariae, putting your stock at risk.
Miracidia (motile, resembling small tadpoles) are released when eggs hatch in the correct conditions (classically spring) and the snail must be penetrated quickly. The life cycle then continues beneath its shell to produce infective cysts on grass; these are then eaten by the grazing cattle and sheep.
What are the signs of Liver Fluke?
It can take a few months for sheep to show signs of fluke and there are two forms of the disease: acute and chronic. In both cases, sudden death can be one of the first indications it is there. Attacks of acute fluke often occur in late summer and autumn, caused by immature flukes that have migrated from the small intestine and then through the liver, as shown below:
Image 1 – Migrating immature fluke travelling from the small intestine to the liver
Chronic fluke is the result of adult F. hepatica in the bile ducts, these are blood feeders, drinking up to 0.5ml a day, which could have been picked up three months before symptoms present. Typically, this infestation becomes evident in winter, however this can occur all year round due to the survival of the mud snails
Image 2 – Adult fluke causing bile duct damage in the liver
How can I protect my flock?
To protect sheep and cattle from chronic liver fluke is to protect them from signs like diarrhoea and anaemia, but more importantly production loss, AHDB estimates liver fluke costs the beef industry £8-9.5 million / year – loss of productivity could be as much as £25 to £30 per beef animal and estimated at £3 to £5 per infected sheep. FSA data show that 6.6% of all sheep livers were rejected due to liver fluke in 2014.
Bottle Jaw (Image 3) is often a well recognised sign in sheep: a swelling appears below the jaw to often indicate low blood protein levels due to the blood feeding adult fluke.
Image 3 – Bottle jaw can occur with Chronic Fluke
The challenge is that the number of mud snails is ever-increasing. Increased rainfall and warmer conditions means this tiny species is able to thrive in our current climate. However, even though wet conditions are optimal, mud snails can also survive dormant for long periods in dry conditions and even under blankets of snow.
In order to tackle the fluke on your farm, there are a number of helpful actions to take. This includes the use of flukicides, but it is vital the correct product is used to target the likely age of the fluke in the stock, it must also be done at the appropriate time, depending on the risks and time of year:
Figure 4; Adapted from: Fairweather, I and Boray, JC (1999) Mechanisms of fasciolicide action and drug resistance in Fasciola hepatica. Chapter 7 In Fasciolosis, Ed JP Dalton. CAB International. pp 225-276 Early immature: 1-5 weeks; Late immature: 6-9 weeks; Adult: >9 weeks Ref: VICH Guideline 12, Efficacy of anthelmintics: specific recommendations for bovines. EMEA, 1999
A risk after treatment is returning the sheep to their original pasture, as no flukicide is persistent. So, drenched sheep should be moved to new pastures to avoid re-infection from mud snails.
A more physical measure includes fencing off areas that the snail thrives in. Sheep and cattle are less at risk where they can’t reach even the muddied edge of shallow waters, which can also house snails. In addition, any bought-in sheep and cattle must be automatically quarantined. They may be infected without showing symptoms, yet spread it to other stock on the farm via your uninfected mud snails.
It is then important to monitor closely all efforts to prevent or contain diseases like fluke:
– Consider the season
– Avoid high risk areas
– Look out for the signs of fluke and utilise abattoir feedback
– Develop a whole farm fluke treatment plan with your vet, SQP or advisor.
For further information have a look at this chart from SCOPS. Got a question about fluke? Maybe you want to know more about protecting your stock? Or just want to stay up-to-date with the latest news about how you can protect your sheep? Tweet and follow us on Twitter: @sheep_farmers and let us know!
For further information, please contact your veterinary surgeon or Zoetis UK Ltd, Walton Oaks, Tadworth, Surrey, KT20 7NS. www.zoetis.co.uk. Customer support: 0845 300 8034. Use medicines responsibly (www.noah.co.uk/responsible).