Molecular analysis of 4/91-like variants of avian infectious bronchitis virus (IBV) obtained after the introduction of a 4/91 live-attenuated vaccine in Costa Rica during 2017.

Abstract

Avian infectious bronchitis virus (IBV) belongs to family Coronaviridae, genus Gammacoronavirus and is one of the most predominant causes of respiratory disease in poultry. Its high mutation rate constantly leads to the emergence of novel variants that complicate disease control. In 2016, a GA13-like IBV outbreak occurred in Costa Rica, prompting the introduction of the 4/91 live-attenuated vaccine. The objective of this research was to perform a molecular characterization of IBV variants circulating in the country six years after the introduction of the 4/91 vaccine. A total of 177 samples from symptomatic birds were analyzed, with 43 testing positive for IBV. Seven complete S1 sequences were obtained and clustered within the GI-13 lineage by phylogenetic analysis. Sequence analysis showed high genetic similarity to the 4/91 vaccine strain, with nucleotide and amino acid sequence identities over 99.13% and 97.96%, respectively, despite these samples being taken from unvaccinated birds. Post-translational modification analysis of the S1 protein revealed conserved N-glycosylation and palmitoylation sites, while two serine phosphorylation changes were predicted between the obtained sequences and the vaccine strain. Selective pressure analysis identified 10 sites under positive selection, mainly located within the receptor-binding domain and hypervariable regions of the S1 subunit. The presence of 4/91-like variants in unvaccinated birds needs attention, and its relation to observed pathology requires further research. Continuous surveillance is essential to monitor for potential vaccine escape mutants and mitigate their impact.

Supplementary information: The online version contains supplementary material available at 10.1007/s13337-025-00910-4.