RECENT wet conditions are possibly set to contribute to an increase in liver fluke, a parasite that costs $100 million in lost production in Australian livestock industries yearly. Experts recommend that cattle producers in fluke-prone areas should be planning the autumn treatment of their herds now – and with research suggesting widespread resistance to the most popular treatment, product choice is now a bit more complicated.
Nick Sangster is a specialist in veterinary parasitology and head of the animal and veterinary sciences school at Charles Sturt University, Wagga Wagga. He is currently involved in research that has found triclabendazole-resistant liver fluke in multiple locations.
“We’ve been out to properties and confirmed that fluke have survived treatment with triclabendazole. We’ve encountered this on the New South Wales South Coast, around Lismore and on the Murray River. In every area we’ve conducted research, we’ve found pockets of resistance.”
Professor Sangster says the best approach is to tackle resistance head on. This means first of all confirming the presence of liver fluke ahead of treatment and then introducing a parasiticide rotation program.
“It’s worth spending the money on proper diagnosis before investing in treatment, and when you are treating, rotation of products really is the best advice. It makes sense that you’re less likely to see the development of resistance issues if you switch between product classes each season.”
Alternatives to triclabendazole for use in cattle include products containing albendazole, clorsulon and/or nitroxynil. There is currently only one product on the market that is non-triclabendazole based and matches its capacity to control all stages of liver fluke – Virbac’s Nitromec injection.
Nitromec contains a combination of nitroxynil and clorsulon, which function synergistically, working together to create a particularly potent impact.
Nitromec is an all-stage liver fluke treatment that can control flukes as young as two weeks old. Traditionally, 'all-stage' treatments have obtained an early immature control claim based on testing against four week old flukes, but studies have shown they perform less well against two week old flukes. However, controlling the earlier stages is very important since these young flukes cause a great deal of damage as they migrate through the animal’s liver, destroying the tissue.
New research suggests that treatments that eliminate very early immature flukes can dramatically improve finishing weights. There has been a demonstrated penalty in the order of 8kg for animals not treated with products that can kill very immature flukes (from two weeks old).
“The earlier you can kill them, the better you’re able to close the window of infection and reinfection,” Professor Sangster said.
Professor Sangster added recent wet weather may lead to a spike in fluke infection but it will be some time before the effects are seen, as the impact of liver fluke can lag a long while behind infection.
“More water means more snails, which are essential in the fluke’s lifecycle, so it’s possible there will be more flukes. With animals more likely to be kept together, because some pastures are too wet for instance, increased infection is likely. But the effects lag well behind infection, even up to a year, so it can be difficult to pinpoint the source. It’s fair to say, though, that water and liver fluke go together.”
Now is the key time for fluke treatment, Professor Sangster says. “You want to treat going into winter so there are no flukes and therefore no eggs accumulating in the environment. That way you can break the cycle and minimise production loss, plus it’s better to go into winter with healthy animals.”
Professor Sangster’s research project is being run in conjunction with Professor Terry Spithill at La Trobe University. Together with Virbac, Professors Sangster and Spithill are hoping not only to identify areas of resistance but also to develop a new and more reliable diagnostic test.
Currently, faecal egg counts are used to confirm fluke and to check for treatment efficacy, but Professor Sangster says the correlation between egg counts and fluke burdens is not reliable. The new test is a faecal antigen test that identifies fluke protein.
“In diseased animals, faecal egg counts can be misrepresentative. For example, as the disease progresses, ‘claypipe’ liver develops, making it harder for the eggs to be released. So, there can be a high fluke burden with a low egg count. We believe that the faecal antigen test will give more reliable results and is sensitive enough to pick up one fluke across several cattle.”
Liver fluke causes infected cattle to show lower growth rates and lower feed conversion rates. The young flukes penetrate the liver capsule and migrate through liver tissue for up to seven weeks before entering the bile ducts to become adult flukes.
The resulting damage can cause death, blood loss, lowered appetite and, in some cases, bottle jaw (swelling under the jaw). Animals suffering from acute liver fluke disease may die with little notice even before showing any signs of illness, making it even more important to treat livestock effectively.