Multiple resistance in Trichostrongylus and Teladorsagia (Ostertagia) in goats to oxfendazole, levamisole and moxidectin, and inefficacy of trichlorphon

Authors: Pomroy WE, Leathwick DM, West DM
Publication: New Zealand Veterinary Journal, Volume 52, Issue 5, pp 298-299, Oct 2004
Publisher: Taylor and Francis

Animal type: Goat, Livestock, Production animal, Ruminant
Subject Terms: Alimentary system/gastroenterology, Animal remedies/veterinary medicines, Anthelmintics, Parasite control, Parasites - internal, Nematode, Treatment/therapy
Article class: Correspondence

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Abstract: We wish to report the identification, from a flock of commercially- traded goats, of nematode worms that we have been unable to kill using the anthelmintic groups currently registered for use in sheep in New Zealand.
There is now considerable concern that these highly-resistant worms could spread to sheep on this property, making conventional worm control difficult, if not impossible, in that host as well. Such highly-resistant worms clearly raise serious problems for the trading of livestock and the future of goat farming in New Zealand. Kidding does indoors and rearing their kids away from pasture may allow the safe introduction of kids onto a farm, but there is no simple way of separating multiple-resistant worms from a host once an infection is established. Extrapolating from the longevity of Trichostrongylus infections in sheep, animals would have to be housed off-pasture for many months before the adult worms in the host would die off naturally, thus making it both difficult and expensive to introduce adult animals without introducing resistant nematodes.
Our key concern is that veterinarians need to be aware that such multiple-resistant worms exist on commercial farms in New Zealand and may be dispersed with traded livestock. The continued movement of goats from this and similar farms will inevitably lead to their presence on other farms and their likely cross-infection into sheep. Farmers should be warned of the risks of introducing goats onto their properties and that quarantine drenching, even when using all three action families, may not necessarily prevent the introduction of resistant nematodes.

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