Evidence for the F200Y (TAC) mutation conferring benzimidazole resistance in a southern USA cattle population of Haemonchus placei spreading from a single emergence

The benzimidazoles are one of the most important broad-spectrum anthelmintic drug classes for the control of parasitic nematodes of domestic animals and humans. They have been widely used in the livestock sector, particularly in small ruminants for over 40 years. This has resulted in the development and wide spread of resistance in small ruminant gastrointestinal nematode parasite species, including Haemonchus contortus. Recently, resistance to benzimidazole drugs has been reported in Haemonchus placei, but there is relatively little information on its prevalence. It is important to develop a molecular tools to identify resistance mutations in H. placei early in their development in order to understand the emergence and spread. Our previous study demonstrated the F200Y (TAC) mutation at their early stage in 6/9 H. placei populations derived from southern USA, albeit at low frequencies between 2 and 10%. The present study analysis the phylogenetics of the isotype-1 {beta}-tubulin locus to suggest that F200Y (TAC) mutation has been spread from a single emergence in H. placei; likely by the anthroprogenic movement of ruminant livestock in southern USA. Population genetic data of H. placei using a panel of microsatellite markers revealed little genetic sub-structure, consistent with a high level of gene flow in this region. Overall, these results provide clear genetic evidence for the spread of F200Y (TAC) benzimidazoles resistance mutation to multiple different locations from a single emergence in H. placei.