Anthelmintic drug resistance in the UK

Abstract

The term 'anthelmintic drug resistance' describes the heritable ability of some nematode parasites to survive treatment with anthelmintic drugs at the recommended therapeutic dose levels. Genes for resistance appear to be present in many of the important pathogenic nematodes of ruminants and horses. Under intensive management systems, where heavy reliance is placed on anthelmintic drugs for worm control, the selection of resistant genotypes may result in increased reports of the drugs failing to control the nematode populations against which they are aimed. Anthelmintic resistance has been reported from many parts of the world, and in some countries multiple drug-resistant strains have emerged. In the UK, recent investigations indicate an increasing level of resistance to benzimidazoles among nematodes of sheep and horses. The incidence, diagnosis, epidemiology and implications of anthelmintic resistance are discussed.

Anthelmintic resistance: The state of play revisited

“…It has been observed that frequent usage of the same group of anthelmintic may result in the development of AR Barton, 1983;Coles, 1986;Waller, 1987;Taylor and Hunt, 1989). There is evidence that resistance develops more rapidly in regions where animals are dewormed regularly.…”

“…However, these actions result in the next helminth generation that consists almost completely of worms that survived therapy and, therefore, might contribute to the development of AR (Smith, 1990;Taylor and Hunt, 1989). For an example, Coles et al (1995) reported problem of AR in the helminths of sheep and goats on some small Greek islands which suffered from extended drought with, in contrast, no AR developed under similar management and deworming practices on the mainland.…”

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

“…It has long been recognised that treating ewes with anthelmintic at this time could be selective for anthelmintic resistance (Brunsdon et al 1983), especially in situations where nematode eggs passed by the ewes contribute signifi cantly to subsequent infection in lambs (Cawthorne and Whitehead 1983;Michel 1985;Taylor and Hunt 1989). In line with this, a modelling study by Leathwick et al (1995) showed that an anthelmintic treatment administered to adult ewes at lamb-docking time could be highly selective for resistance where it both pre-selected larval challenge to lambs and removed a source of unselected nematodes in refugia.…”

Duration of Anthelmintic Effect of Three Formulations of Ivermectin (Oral, Injectable and Pour-on) Against Multiple Anthelmintic-Resistant Haemonchus contortus in Sheep

“…Chemotherapy using broad-spectrum anthelmintics remains the mainstay of control of GI nematodosis. Furthermore, the intensification of animal production systems has lead to increasing dependence on anthelmintics (Taylor and Hunt, 1989) and regular suppressive dosing of susceptible livestock has resulted in the development of resistance in GI nematodes throughout the world. In India, GI parasites are currently controlled by four major groups of anthelminticsbenzimidazoles, imidazothiazoles, salicylanides and avermectins.…”