Evidence that moxidectin is a greater risk factor than ivermectin in the development of resistance to macrocyclic lactones by Ostertagia spp in sheep in south eastern Australia

Abstract

Use of MOX for > or =2 of the preceding 5 years was associated with a higher prevalence of resistance to ML by Ostertagia spp on sheep farms in south eastern Australia than the use of IVO.

A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep

“…However, as the anthelmintic concentration slowly subsides to sub-lethal concentrations, both homozygousand heterozygous-resistant parasites are able to establish within the host, while homozygous-susceptible parasites still cannot establish, thereby accelerating the development of AHR (Sutherland and Scott, 2010). While several studies have investigated the role of long-acting formulations as a putative risk factor for AHR (Le Jambre et al, 1999;Sutherland et al, 2000;Leathwick et al, 2006;Rendell et al, 2006;Hughes et al, 2007), only two studies were suitable for quantitative data extraction and synthesis (Rendell et al, 2006;Hughes et al, 2007); the pooled estimate showed a marginally significant positive association between the use of long-acting formulations (either as moxidectin or macrocyclic lactone capsules) and AR (Fig. 5).…”

“…Another factor frequently investigated was the use of long-acting anthelmintic drugs (Le Jambre et al, 1999;Sutherland et al, 2000;Leathwick et al, 2006;Rendell et al, 2006;Hughes et al, 2007). These drugs have a persistent action, either because of an innate drug characteristic (e.g.…”

“…Similarly, the removal of Rendell et al (2006) from the MA for use of long-acting formulations significantly reduced the overall pooled estimate (OR = 1.55; 95% CI = 0.75, 3.23) and the observed heterogeneity (I 2 = 0%). No other significant changes were observed when the analyses for the other three factors were repeated.…”

“…5). The odds of AHR in flocks that used long-acting formulations was 2.85 (95% CI: 0.79, 10.24) times higher than those in flocks that either did not use any anthelmintic (Hughes et al, 2007), or only used short-acting ivermectin drench (Rendell et al, 2006). The heterogeneity between the studies was high (I 2 = 70%; p = 0.04 for test of heterogeneity).…”

Prevalence of anthelmintic resistance on sheep farms in New Zealand

“…While Ostertagia spp are implicated as the parasite most likely to be resistant to ML, it is by no means the only genus involved, as shown similarly by Hughes and McKenna (2005) (Rendell et al 2006).…”