Abstract
Haemonchus contortus is widely distributed in the world, which is seriously harmful to small ruminants and has serious resistance to common anthelmintics. Over time, the prevalence and intensity of host infection with this parasite have gradually increased, so it is necessary to study the phylogenetic and genetic changes of single anthelmintic resistant strains. This study is the first to analyze the genetic diversity and population structure about IVM-resistant H.contortus (L3,egg, adult, n = 30 ) in Inner Mongolia, China. The H.contortus were identified to IVM resistance and cultured by fecal egg count reduction test, larval development inhibition test and larval locomotor behaviour test. The complete sequence of ITS2 ( second internal transcribed spacer ) and partial sequence of nad4 ( nicotinamide dehydrogenase subunit 4 gene ) in L3, adult and egg were amplified. At the same time, compared with the ITS2 and nad4 partial sequences of H.contortus reported in NCBI database to carry out phylogenetic analysis and haplotype determination, so as to further study the variation and population genetic diversity of IVM-RR samples. The samples were identified as H.contortus resistant to IVM. Phylogenetic analyses of ITS2 of IVM-RR and other H.contortus showed that they were from the same branch, genetic relationship was close, the intraspecific was relatively conserved, and no significant correlation with AR. There was no significant difference between different stages of development of the samples. In addition, from the 30 nad4 gene sequences of IVM-RR samples obtained 13 haplotypes, and the 169th base site in 70% of the nad4 gene was mutated. The nucleotide diversity was 0.00623 and haplotype diversity was 0.926. IVM-RR compared with five countries' H.contortus nad4, found that the genetic differentiation level of the IVM-RR population was relatively low with the China and Pakistan populations, and the Fixation index (Fst) were 0.10957 and 0.17262, respectively. The genetic differentiation levels with Bangladesh, Greece and France populations were higher, and the Fst values were 0.46978,0.61825 and 0.98101. Perhaps the population structure differentiation were correlated with regional localization and anthelmintic frequency treatment. In this report, we analyzed the genetic diversity and population differentiation of IVM resistant H.contortus at different developmental stages, and obtained resistant samples' haplotypes, hoping to provide a new direction for the study of AR and vaccine research.