Resistant liver fluke found in Welsh flock

By Farmers Weekly staff

LIVER fluke resistant to one of the widely used drugs has been confirmed in west Wales.

In a letter to the Vet Record, 12 February, Islwyn Thomas and Gerald Coles of the University of Bristol, and Carmarthenshire vet Kate Duffus, report the presence of fluke eggs in ewes following treatment with triclabendazole.

Resistance of liver fluke to triclabendazole treatment has previously only been confirmed in Australia and Scotland, it adds.

This case of resistance was in ewes grazing a field with a boggy area, treated with triclabendazole twice last summer and autumn.

But even after a third supervised treatment with the product, faecal samples contained fluke eggs.

But these resistant fluke were easily killed using another flukicide. Seven days after ewes were treated with clostanel (Flukiver), no fluke eggs were found in samples.

Dr Coles is concerned that resistance will spread in the UK. “This could be the tip of the iceberg. I understand resistance in Australia is widespread.

“Producers should be aware that if they use this product, it cannot be guaranteed to remove fluke any more. However, it will still work on most farms.”

But Craig Stevenson of Novartis Animal Health who markets triclabendazole as Fasinex flukicide and together with a wormer in Combinex, says resistance is still rare.

This is only the second case of resistance reported in Britain, and triclabendazole remains the only treatment for fluke at three life-cycle stages.

“The number of resistance cases is low world-wide.

In Australia, liver fluke is a major problem, but cases of resistance are limited to one specific area,” says Mr Stevenson, who is currently working in the UK but is on secondment from Novartis Australia.

He says that other suspected resistance cases have been reported in the UK but have resulted from re-infection or a parasitic worm which also causes bottle-jaw in sheep.

Dr Coles advises producers concerned that fluke are not being killed to stop relying on just one drug.

“If you suspect a problem use a clostanel-based drug and, if animals improve, you can be fairly sure fluke are resistant.”

But he warns there is no evidence that rotating drugs will reduce resistance risks.

However, Mr Stevenson urges producers to contact Novartis through their vet if resistance is suspected, so cases can be investigated.

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