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Take Caution When Selecting Flukicide

25 November 2010

UK - Leading experts are urging farmers to limit their use of triclabendazole (TCBZ) for treating liver fluke in cattle, because over-use can result in increased risk of parasite resistance to the drug, and therefore reduced usefulness for treating sheep.

Dr Theo De Waal BVSc, PhD, Senior Lecturer at the School of Agriculture, Food Science and Veterinary Medicine at University College Dublin, says: “Triclabendazole (TCBZ) is particularly useful for treating the early immature and immature stages of liver fluke. These stages are especially critical for sheep because they can suffer acute disease or death as the early fluke stages travel in large numbers through the liver. Generally, in cattle it is the mature fluke which cause more of a problem, as these stages cause subclinical or production disease, leading to a loss of condition and an increase in finishing time for producers.

“Fluke can become resistant to TCBZ the more frequently they are exposed to the flukicide There have already been reports of triclabendazole-resistant fluke in sheep in Ireland and parts of the UK over recent years. As it is the same fluke which can infect both cattle and sheep, it is possible that where cattle and sheep are grazing the same pastures cattle can become infected with resistant fluke picked up from the pasture. More importantly it is also possible that by treating cattle with TCBZ the risk of developing resistant fluke is increased and these resistant fluke can then infect sheep.”

Professor David Logue, Professor of Food Animal Disease at the University of Glasgow, agrees that there is a problem. “Triclabendazole resistance certainly seems to be increasing in sheep flocks,” says Professor Logue.

“It is the most effective flukicide against the early immature stages of the parasite, which can cause acute or sub-acute disease and death in sheep. Using TCBZ less frequently is likely to slow the development of resistance and preserve its usefulness in situations where acute infection is likely.

“The use of a flukicide other than triclabendazole is sensible wherever it is thought likely that the infection causing the illness or poor performance is due to mature or late immature stages of fluke. It is exactly the same principle as applies to the rotation of roundworm products to reduce the build-up of resistance. This kind of caution should be applied to use of TCBZ in both cattle and sheep.”

Dr de Waal urges caution particularly in the use of triclabendazole with cattle. He says: “Routine use of TCBZ in cattle is likely to increase the pressure of resistance build-up in fluke, thus reducing or negating its efficacy in sheep.”

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