Genetic and Antigenic Diversity of Infectious Bronchitis Virus in South America

Infectious bronchitis virus (IBV) is one of the economically most important diseases affecting the South American poultry industry. The extensive genomic heterogeneity of IBV is a consequence of high mutation rates and recombination events followed by selection. Nucleotide heterogeneity is much higher in the S1 coding region of the relevant spike protein; thus, the S1 sequence is widely used for the IBV genetic classification in genotypes and lineages. Two main lineages (GI-11 and GI-16) extensively circulate in South American chicken flocks. The GI-11 lineage, found exclusively in South America, emerged in the 1950s and is currently the predominant lineage in Brazil and Uruguay. The GI-16 lineage emerged around 1979 and is now circulating in most South American regions. All South American countries include Massachusetts-type strains (GI-1 lineage) in the IBV vaccination programs. The GI-11 and GI-16 lineages display very low antigenic relatedness to Massachusetts vaccine strains. Because these vaccine strains may not confer complete protection against South American lineages, other vaccination strategies have been reported to control GI-11 and GI-16 outbreaks. Analysis of the few full-length genomes of South American strains highlights a complex recombination history of IBV in the continent. A broader geographic and temporal sampling is needed to understand the pattern of genetic variability and the evolutionary history of IBV variants in South America.