Anthelmintic Resistance in Haemonchus contortus of Sheep and Goats from Asia-A Review of In Vitro and In Vivo Studies

The potential of Haemonchus contortus is quite impressive to acquire resistance to anthelmintic drugs. Asian field populations of H. contortus are reported to exhibit resistance to most of the anthelmintic drug families, including closantel, imidazothiazoles, macrocyclic lactones and benzimidazoles. This review paper comes up with a comprehensive overview of haemonchosis with anthelmintic resistance (AR), with particular attention to studies conducted in regions of Asia. It also confers the prevalence and mechanisms in H. contortus for anthelmintic resistance, indicating the necessity for alternative approaches to control the pathogen. Several SNPs identified in gene isotype-1 beta-tubulin gene have been discussed that are associated with benzimidazole resistance and are prevalent in H. contortus populations in Asia. The methods used by H. contortus to withstand the effects of these medications are examined together with the history of how resistance to different anthelmintics in this species has developed. The approaches for diagnosing resistance are also compiled in this review. Such diagnosis currently largely relies on the fecal egg count reduction test, which has cost and sensitivity issues. Past and present efforts to use less expensive and time-consuming phenotypic assays with free-living life stages are also described with the developmental progress of molecular assays to provide sensitive resistancedetection tests. Overall, this paper provides valuable perception into the current understanding of AR in Haemonchus spp. and the challenges faced in the management of this disease in Asia.