Molecular Characterization and Detection of Brachyspira pilosicoli Associated with Intestinal Dysbiosis of Layer Chickens on the Indian Subcontinent.

Avian intestinal spirochetosis, caused by Brachyspira species, significantly impacts chicken flocks worldwide, leading to economic losses due to mortality, reduced egg production, and lower-quality eggs. Despite India's substantial poultry population, the importance of Brachyspira has been overlooked. This study investigated the significance of Brachyspira spp. in layer chicken flocks in India. This is a primary report to determine the incidence of Brachyspira pilosicoli from layer flocks in the country. The study sampled 25 layer chicken farms between March and December 2023 from which 250 cecal swabs were processed for Brachyspira isolation, molecular confirmation made using PCR and its phylogenetic analysis. The results showed that two out of 25 farms were positive for B. pilosicoli by culture and PCR. The positive flocks, aged between 50 and 72 wk, reared in a cage system in open-sided houses. The litter conditions were semisolid, with an abnormal odor and brownish color, indicating dysbiotic changes. The affected flocks experienced a drop in egg production of up to 12%-15%, fecal-stained eggs up to 0.4%-0.6%, and pasty vents and mortality rates of 1.5% and 5.7%, respectively. Postmortem examination revealed ballooning of the ceca with yellowish-light brown moist contents and inspissated, amorphous yolk material in the abdominal cavity. The histopathological examination of the cecum showed loss of villi and crypts along with infiltration of inflammatory cells. Sequencing and phylogenetic analysis showed 99.73% to 100% identity of the Indian B. pilosicoli sequences with the reference sequences from Australia, France, and the United States.