GASTROINTESTINAL STRONGYLES OF RUMINANTS : MECHANISMS OF ANTHELMINTIC RESISTANCE AND CONSEQUENCES ON THEIR MANAGEMENT

The management of gastrointestinal strongyle infestations in ruminants relies mostly an anthelmintics. Only three chemical families are available, and gastrointestinal strongyles resistance is increasing. The resistance mechanisms are relatively well known for benzimidazoles (involving one gene with two alleles), whereas the genetic determinism of the resistance to macrocyclic lactones or imidazothiazoles (levamisole) is still poorly understood, but probably involves multigenic regulation. A double approach (candidate genes and transcriptomic) is proposed for levamisole resistance and the first results are presented. It is very important to understand resistance mechanisms to reduce their occurrences. Examples with benzimidazoles are presented to describe interactions between the type of genetic mechanism and the speed with which resistance appears and expands, the efficacy of selective pressure by treatments, and the role of refugia.