Project shows increasing resistance to wormers

RESISTANCE to wormers has increased in Wales since the previous study in 2006, including those products previously considered effective at killing the parasites in sheep.

These are the preliminary results from a project into anthelmintic resistance overseen by Hybu Cig Cymru (HCC) and funded by the Rural Development Plan for Wales. The initial results indicate that the extent of anthelmintic resistance has increased. Anthelmintic resistance means that the wormer loses effectiveness because a proportion of the worms are resistant and survive treatment.

Generally this process occurs over several years but if detected at an early stage, famers can adopt practices to maintain the wormer’s useful life for longer. The Wales Against Anthelmintic Resistance Development (WAARD) project is half way through its surveillance on 45 farms.

The three older wormer groups (1-BZ, 2-LV and 3-ML) have been tested as well as a separate test on Moxidectin (a member of the 3- ML group with persistent action), to see how effective they are. The test involves looking at faecal egg counts (FEC), before and after treatment and calculating the percentage reduction. To be fully effective the count must drop by at least 95 per cent. A reduction of less than 95 per cent suggests that there are resistant worms present.

Of the 24 farms tested so far, 83 per cent have evidence of resistance to White (1- BZ) and 67 per cent to Yellow (2-LV) drenches. While this represents an increase compared to previous surveys, it is no real surprise. Resistance has also been detected on 29 per cent of farms to the Clear (3-ML) wormer group and on 21 per cent of farms tested so far there is evidence of resistance to Moxidectin.

Moxidectin is tested separately because although it is a member of the 3-ML group only rare instances of resistance has previously been recorded, with Moxidectin remaining effective even where other 3-ML products such as ivermectin are failing. “These results are therefore, of concern,” said Eirion Thomas of Techion UK, who is carrying out the research on behalf of HCC.

“Additionally four of these farms have evidence of worms that are resistant to all four of the wormers tested. The challenge will be to help them maintain their worm control in the future.“ HCC technical development executive Lynfa Davies said: “This is an important project providing sheep farmers with valuable information about the level of resistance to these drugs.”

“While the preliminary results are worrying HCC, together with SCOPS, will work to provide clear messages to farmers to help them understand and react to these findings.”

Lesley Stubbings, sheep consultant representing SCOPS, said: “We shouldn’t be surprised by these results because we know that the incidence of anthelmintic resistance has continued to increase in recent years. “The detection of Moxidectin resistance on one in five of the farms, however, is a real concern and a very timely reminder that we must act fast if we are to maintain good worm control on sheep farms.”

The project runs until June 2015 and the remaining farms will be tested in the spring and early summer.

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