Molecular evidence of Histomonas meleagridis in Ascaridia galli from chickens in Thailand: Possibility of transmission pathways

The poultry industry in Thailand plays a vital role in national food security and economic stability. Ascaridia galli is among the most prevalent and pathogenic nematodes affecting chickens, contributing to significant losses in global poultry production. Histomoniasis, another serious disease, causes severe liver and caecal lesions and high morbidity. Despite the importance of both parasites, the information of the molecular characterization of A. galli and the detection of Histomonas meleagridis within adult A. galli in Thailand is still limited. In this study, cytochrome c oxidase subunit 1 (COI) and 12S ribosomal RNA (12S rRNA) genes were amplified by polymerase chain reaction (PCR) from 20 adult Ascaridia nematodes. Additionally, 18S ribosomal RNA (18S rRNA) gene amplification was performed to confirm H. meleagridis infection. The resulting sequences were aligned and compared with reference sequences of A. galli, H. meleagridis, and other related protozoa. Both COI and 12S rRNA sequences confirmed the identity of the nematodes as A. galli. Notably, H. meleagridis DNA was detected exclusively in female A. galli specimens. These findings suggest that female A. galli may act as a potential reservoir host in the transmission cycle of H. meleagridis in chickens. This study represents the molecular evidence of H. meleagridis DNA within A. galli collected from the intestinal contents of deceased chickens clinically suspected of histomoniasis.