Microsatellite analysis reveals extensive gene flow, and lack of population structure in the farm populations of Haemonchus contortus in northern China.

The parasitic nematode Haemonchus contortus is economically an important parasite of small ruminants across the globe. China is the world's largest producer, consumer, and importer of mutton. With ubiquitous distribution across the country H. contortus is one of the potential candidates to cause huge economic losses to small ruminant farming industry in China. We herein investigated genetic diversity and population structure of six farm populations of H. contortus in northern China, and also compared them to H. contortus isolates from UK and Australia. We first prepared individual DNA samples from 240 adult worms, and generated genotyping data using eight microsatellite markers. Obtained data was then subjected to allelic frequency and population genetic analyses. The overall allelic richness (mean/locus/pop = 7.375 ± 0.844-10.125 ± 1.109), and expected heterozygosity (mean/locus/pop = 0.646 ± 0.040-0.735 ± 0.025) indicated high degree of population genetic variation across the Chinese isolates. Low level of genetic differentiation (Fst = 0.010-0.066) was observed across all the populations. AMOVA results showed high level of variation (93%) within the populations. PCA analysis revealed mixed clustering of all the populations with no visible geographical sub-structuring. Finally the population admixture analysis resulted in extensive admixing of genotypes across all the populations. With these findings we conclude that there is no obvious population genetic structure with extensive gene flow across all the farm populations of H. contortus in northern China.