Genetic diversity and population structure of <i>Haemonchus contortus</i> isolates from sheep across Xinjiang, China

<i>Haemonchus contortus</i>, a highly pathogenic gastrointestinal nematode, significantly impacts small ruminant production, causing substantial economic losses in sheep and goat farming. This study examined the genetic diversity and population structure of 171 <i>H. contortus</i> isolates collected from the abomasa of sheep slaughtered across 8 distinct regions in Xinjiang, China. Using sequence analysis, phylogenetic reconstruction and population genetic analyses of the mitochondrial <i>nad4</i> gene, we identified 163 haplotypes, with haplotype diversity ranging from 0.995 to 1.000 and nucleotide diversity from 0.02007 to 0.03145. The Tacheng population displayed the highest nucleotide diversity. Analysis of molecular variance revealed that 91.83% of genetic variation occurred within populations, with minimal differentiation among them (Fst: -0.01296 to 0.04274). Neutrality tests (Tajima's D and Fu's Fs) indicated no recent population bottlenecks. Phylogenetic and haplotype network analyses showed no distinct geographic clustering, suggesting extensive gene flow, likely facilitated by host movement. These findings provide critical insights into the genetic structure of <i>H. contortus</i> in Xinjiang, informing strategies for managing anthelmintic resistance and controlling this economically significant parasite.