Molecular identification and Genogrouping of chicken infectious anaemia virus from commercial layer flocks of Gujarat, India.

Abstract

This study was conducted to ascertain the positive incidence, genogrouping, and amino acid variations in the VP1 gene of chicken infectious anaemia virus (CIAV) among layer flocks in Gujarat, India. A single pooled sample was collected from each of the 32 farms visited, all of which had a history and post-mortem lesions suggestive of chicken infectious anaemia (CIA) across five districts of the state. Samples were processed, and CIAV was confirmed by PCR targeting the VP3 gene and genogrouped. In histopathological examination, generalised lymphoid atrophy with prominent lymphocyte depletion was observed in both the cortex and medulla of the thymus and bursa of Fabricius. Out of the total 32 pooled tissue samples, 21 (65.63%) tested positive for the presence of CIAV. The effect of vaccination on disease prevention was found to be nonsignificant, as all five vaccinated flocks (100%) tested positive. Upon phylogenetic analysis, these isolates were found to be virulent and of genogroup IIIb (sub-clade G-II-b of clade G-II), but distant to strains of genogroup IIIa and II. The notable amino acid difference of C149M/E was similar to the change reported from South India in 2022. Amino acids were different from IIIa strains at V75I, L125I, K139Q, S287A, and G370S positions, Cux-1 vaccine at V157M, S287T, and G370S, and group I strains at L125I positions. The possession of virulence-determining amino acids, variations from vaccine strains and IIIa field strains, and divergence from other Indian strains might be the cause of escape from vaccinal immunity.