Molecular characterization of a novel variant of infectious bronchitis virus from field outbreaks in backyard chicken population of North East India

Abstract

Infectious bronchitis virus (IBV) causes considerable economic impacts on global poultry production. Since its emergence in early 1930, IBV continues to evolve and now exists in a wide range of antigenically and genetically distinct variants, that makes the prevention and the control of the disease both complex and challenging. Although IBV has been reported regularly from different corner of India, information about the molecular epidemiology of circulating strain in relation to clinical form of the disease is not available. We have studied the clinico-pathology and confirmed eight distinct field outbreaks of the disease from poultry population of Mizoram, India. The clinical disease in affected birds resulted sever pathological lesions involving respiratory, gastrointestinal, and urinary system together. The complete S1 nucleotide sequences and protein analyses have revealed a distinct variant of genotype I-IBV (GI), designated as GI-24 circulating in India. The S1 protein of the field strains displayed unique additional eighteen amino acids at C terminal end when compared with M41strain. Comparison of the S1 protein among all the 27 lineages of GI revealed five mutations that are exclusive to only the Indian strains. All the field strains have also possessed the amino acid mutations at highly variable region 2 (HVR2) of S1 receptor-binding domain (RBD) that are considered characteristic of nephropathogenic strains. The circulating GI-24 strains displayed potency for a wide range of tropism from respiratory epithelium to GIT and urinary system. This study provides insight on recently emerging IBV outbreaks in NER, India, which might be causing huge economic losses to the poultry farmers in the region.

Keywords: Backyard poultry; Genotype GI-24; India; Mizoram; Phylogenetic analyses; S1 protein.