Identification of a Novel Isolate of the Poultry Roundworm Ascaridia galli and Its Egg Embryo Developmental Dynamics In Vitro

Ascaridia galli is a major gastrointestinal nematode of poultry that causes significant economic losses worldwide. In this study, we characterized a new isolate, A. galli AgSC_2025, obtained from Xichuan black-bone chickens in China, using an integrative approach by combining morphology, scanning electron microscopy (SEM) and mitogenomics and then its complete developmental changes in eggs—the primary source of infection—was also documented using a high-resolution auto-microscopic imaging. The adult worms exhibited diagnostic characteristics of A. galli, including three distinct lips and a specific arrangement of male caudal papillae. Molecular analysis showed a 99.84% mitogenome identity with previously reported A. galli and positioned the isolate and A. galli in one branch which was sister to other congeneric species within the Ascaridia clade. Furthermore, the high-resolution auto-microscopic imaging system yielded a detailed and complete in vitro egg developmental dynamics with thirteen distinct stages, ranging from the initial 1-cell stage to the infective third-stage larva (L3); and further developmental timeline emphasized that the infective L3 larvae predominated by day 10, with 100% reaching this stage on day 13. Viability assays demonstrated a 79.8% ± 0.46% larval hatching rate and the high vitality of the liberated larvae among these infective eggs. These findings provide a comprehensive morphological and molecular reference for this A. galli isolate and also establish precise developmental biological parameters for egg embryonation, which should offer valuable insights for species-specific identification and the optimization of sanitation protocols to control avian ascaridiasis.