Morpho-molecular characterization and phylogenetic analysis of the Heterakidae nematode isolated from free-range chickens in the Sulaymaniyah Province, Iraq.

Background and Aim: Heterakis gallinarum is a parasitic nematode that commonly infects the ceca of domestic and wild gallinaceous birds, acting as a vector for Histomonas meleagridis, the causative agent of blackhead disease. Despite its significance in poultry health, molecular data from Iraq, particularly Sulaymaniyah province, remain limited. This study aimed to characterize the morphological and genetic features of H. gallinarum isolated from free-range chickens in Sulaymaniyah using mitochondrial cytochrome c oxidase subunit 1 (COX1) gene sequencing. Materials and Methods: A total of 140 free-range adult chickens were purchased from local markets in Sulaimani city between January 2023 and October 2024. Birds were euthanized, and cecal contents were examined for Heterakis spp. Adult worms were morphologically identified under light microscopy. DNA was extracted from representative isolates, and the COX1 gene was amplified using polymerase chain reaction (PCR) and sequenced. Phylogenetic analysis was conducted using the neighbor-joining method based on the Kimura-3 parameter model. Results: Out of 140 chickens examined, 51 (36.43%) were infected with H. gallinarum. Morphological analysis revealed typical features, including unequal spicules in males and barrel-shaped eggs. PCR confirmed a 1325-bp COX1 gene fragment. Basic Local Alignment Search Tool analysis showed 98%-99% similarity with known H. gallinarum sequences. Phylogenetic reconstruction clustered the Iraqi isolate (GenBank: PQ395216.1) with isolates from China, South Africa, Tunisia, and Bangladesh, indicating low genetic divergence across geographic regions. Conclusion: This is the first molecular documentation of H. gallinarum in free-range chickens from Sulaymaniyah, Iraq. The findings highlight the widespread genetic conservation of this parasite and underscore the need for further epidemiological studies to determine risk factors and potential impacts on poultry productivity.