Genetic analysis of inbreeding of two strains of the parasitic nematode Haemonchus contortus.

Haemonchus contortus is a sheep parasitic nematode that causes severe economic losses. Previous studies have indicated a high degree of genetic heterogeneity, which is hardly affected by selection for drug resistance. As a tool for the analysis of the population dynamics of H. contortus and its response to drug resistance, we designed a strategy to study the inbreeding of a benzimidazole-sensitive and a benzimidazole-resistant strain. After 15 generations, a theoretical inbreeding coefficient of 0.87 was achieved. The different stages of inbreeding were analysed using restriction fragment polymorphism, microsatellite variability and amplified fragment length polymorphism. Model-based clustering of the amplified fragment length polymorphism genotypes showed that the allele frequencies of the benzimidazole-resistant strain were stable during the last eight generations. In the sensitive strain a gradual shift of allele frequencies was observed, which led to a temporary increase of the genetic diversity around the eight generations.