High level of treatment failure with commonly used anthelmintics on Irish sheep farms

Abstract

BackgroundIn 2013 a Technology Adoption Program for sheep farmers was established to encourage the implementation of best management practices on sheep farms in Ireland. There were 4,500 participants in this programme in 2013. As part of this programme, farmers had the option to carry out a drench test to establish the efficacy of their anthelmintic treatment.ResultsFlock faecal samples were collected before and after treatment administration and gastrointestinal nematode eggs enumerated. In total there were 1,893 participants in the task, however only 1,585 included both a pre- and post-treatment faecal sample. Of those, 1,308 provided information on the anthelmintic product that they used with 46%, 23% and 28% using a benzimidazole (BZ), levamisole (LEV) and macrocyclic lactone (ML) product respectively. The remaining farmers used a product inapplicable for inclusion in the task such as a flukicide or BZ/LEV combination product. Samples were included for analysis of drench efficacy if the pre-treatment flock egg count was ≥200 eggs per gram and the interval post-sampling was 10–14 days for BZ products, 4–7 days for LEV products and 14–18 days for ML products. These criteria reduced the number of valid tests to 369, 19.5% of all tests conducted. If the reduction post-treatment was ≥95% the treatment was considered effective. Only 51% of treatments were considered effective using this criterion. There was a significant difference in efficacy between the anthelmintic drug classes with BZ effective in only 30% of treatments, LEV effective in 52% of cases and ML effective in 76% of cases.ConclusionsGastrointestinal nematode anthelmintic treatments, as practiced on Irish farms, have a high failure rate. There was a significant difference between the efficacies of the anthelmintic classes with BZ the least effective and ML the most effective.

Widespread anthelmintic resistance in European farmed ruminants: a systematic review

“…Insufficient data were available to estimate mean prevalence for other anthelmintic classes and cattle. The prevalence of AR has also been estimated elsewhere, for example, treatment failure has been identified on 51 per cent of Irish sheep farms surveyed (Keane and others 2014) and 64 per cent of Scottish sheep farms surveyed (Bartley and others 2003). These studies provide valuable prevalence estimates, but the differences in sample (farm) selection methods introduce potential sample selection bias and may affect estimates and comparability between regions.…”

A real-time PCR approach to identify anthelmintic-resistant nematodes in sheep farms

“…For example, in the UK, Bartley et al (2006) observed a similar range of low efficacy of IVM (66% to 92% of egg reduction) in 6 of 17 naturally grazing flocks in south/central Scotland. Moreover, in a largescale survey, Keane et al (2014) observed low efficacy of macrocyclic lactones in 24% of 1308 studied farms in Ireland. This is in contrast with data obtained in some Mediterranean climates such as in Campania region (southern Italy) where all tested anthelmintic drugs including IVM remained totally effective (Rinaldi et al 2014).…”

“…Increasing issues of anthelmintic resistance (AR) are encountered in tropical countries (Almeida et al 2010;Mahieu et al 2014), but recent studies demonstrated that most European countries were more and more facing this issue (Rose et al 2015). In almost all sheep markets in Europe, AR to benzimidazoles (BZ) has been described (Papadopoulos et al 2012); however, ivermectin (IVM) and moxidectin (MOX) resistances are still less frequent in Europe than in the southern hemisphere with the noticeable exception of the UK (Bartley et al 2006) and Ireland (Keane et al 2014). BZ resistance has been frequently described in mainland France (Chartier et al 1998;Geurden et al 2014).…”

An independent validation study of loci associated with nematode resistance in sheep

“…; Keane et al . ). Selective breeding for resistance to nematode infection is a complementary and sustainable method for controlling the effects of nematodes on ruminants (Riggio et al .…”