Genetic diversity and morphotypes of Haemonchus contortus in sheep in Thailand: A combined morphological and molecular approach

Haemonchus contortus is a highly pathogenic gastrointestinal nematode of small ruminants, yet molecular information on sheep-derived isolates in Thailand remains limited. This study aimed to characterize H. contortus recovered from sheep in Nakhon Pathom Province using integrated morphological and molecular approaches. Adult nematodes collected post-mortem from the abomasum were examined morphologically, and the internal transcribed spacer 2 (ITS2) region of ribosomal DNA was amplified and sequenced. Morphological examination identified males with characteristic copulatory bursae and females exhibiting linguiform, knobbed, and simple vulvar morphotypes. ITS2 sequences showed 95.26–98.11% identity with reference H. contortus sequences deposited in GenBank. Molecular and phylogenetic analyses supported the identification of the examined sheep-derived isolates as H. contortus. These findings provide baseline morphological and ITS2 sequence data for H. contortus in sheep from Nakhon Pathom Province. Broader sampling across farms and geographical regions, together with additional mitochondrial and nuclear markers, would help clarify genetic diversity and population structure in Thai sheep.