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Anthelmintic resistance: potential benefits of ‘over-diagnosis’
  1. N. D. Sargison and
  2. P. R. Scott
  1. University of Edinburgh, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Roslin, Midlothian, EH25 9RG

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Neil Sargison and Philip Scott respond to the view expressed by Ian Fairweather in a recent Viewpoint that unconfirmed reports of resistance to triclabendazole may be hampering the control of fasciolosis, suggesting instead that they might help raise awareness of more sustainable management strategies

IAN Fairweather (2011a) reasons that unconfirmed reports of Fasciola hepatica resistance to triclabendazole may be hampering the control of fasciolosis by encouraging farmers to use less efficient products, and recommends more accurate laboratory diagnosis before claims of resistance are made (Fairweather 2011a). In the spirit of entering into constructive discussion, we would like to challenge this viewpoint.

We acknowledge that lack of anthelmintic efficacy is not necessarily synonymous with anthelmintic resistance and that lack of efficacy of triclabendazole against F hepatica sometimes arises following underdosing, putatively brought about by: underestimation of animals' bodyweight; failure to administer the correct dose; poor product storage; or the use of inferior-quality products. Reports of resistance that do not take these factors into account should be questioned, although the relevance of other factors such as the effects of liver disease on the pharmacology and fasciolacidal activity of triclabendazole may be overemphasised (Halferty and others 2009).

The diagnosis of triclabendazole resistance is not straightforward, but we respectfully challenge the contention that only the Sligo isolate of F hepatica (Fairweather 2011b) has been proven to be genuinely resistant. Professor Fairweather …

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