Molecular Characterization of Haemonchus contortus (Nematoda: Trichostrongylidae) from Small Ruminants in Thailand Based on the Second Internal Transcribed Spacer of Ribosomal DNA

The genetic variation of Haemonchus contortus in Thailand was studied including its relationship with Thai samples and relevant sequences. The second internal transcribed spacer (ITS2) of the rDNA sequence of H. contortus, a large stomach worm of small ruminants, was amplified and sequenced from 158 individual worms isolated from small ruminants (goats and sheep) distributed over 11 provinces in Thailand—Chiang Mai, Mae Hong Son, Krabi, Prachuap Khiri Khan, Buriram, Chaiyaphum, Suphanburi, Phra Nakhon Si Ayutthaya, Saraburi, Kanchanaburi and Ratchaburi. The analysis of nucleotide sequences revealed 21 genotypes (G1–G21). G1 and G2, comprising 62 and 55 individual worms, respectively, were predominant in the study. The results showed that genotype diversity was relatively high, with 12 polymorphic sites over 231 bp detected. The pairwise sequence identity of H. contortus was 98.4%. Comparing these sequences with those of H. contortus and H. placei derived from the GenBank database provided average results of 98.5% and 96.9%, respectively. Phylogenetic investigations using the UPGMA method found that H. contortus from the 21 genotypes in Thai populations was divided into two groups—group A and a separate group B containing G5 and G13. On a global scale, all Thai genotypes and sequences from the GenBank database of H. contortus were also related and grouped into the same cluster, The outgroups (H. placei) at both trees—the national and global scale were separated into a distinct cluster. The genetic information obtained in this study will be useful in many areas, including integrated approaches to issues such as farm management and anthelmintic drug treatment for haemonchosis infection.