Antigenic and molecular characterization of isolates of the Brazilian genotype BR-I (GI-11) of infectious bronchitis virus supports its recognition as BR-I serotype

ABSTRACT

The antigenic and molecular characteristics of BR-I infectious bronchitis viruses (IBVs) isolated from Brazil are reported. IBVs isolated from commercial flocks with different clinical manifestations between 2003 and 2019 were submitted to antigenic and molecular characterization. The complete S1 glycoprotein gene of 11 field isolates was amplified and sequenced. The virus neutralization (VN) test showed 94.75% neutralization with a BR-I isolate and 30% or less against other worldwide reference strains. The nucleotide and amino acid sequence analyses revealed 84.3–100% and 83.5–100% identity among them, respectively. The identity values ranged from 57.1 to 82.6% for nucleotides and from 46.6–84.4% for amino acids compared with those of other genotypes. By phylogenetic tree analysis, the Brazilian isolates were branched into the BR-I genotype (lineage GI-11), which was differentiated from foreign reference strains. Selective pressure analyses of BR-I IBVs revealed evolution under purifying selection (negative pressure) for the complete S1 gene but four specific sites (87, 121, 279, and 542) under diversifying selection (positive pressure). Profiles of cleavage sites and potential N-glycosylation sites differed from those of other genotypes. The low molecular relationship among the Brazilian viruses and foreign serotypes was concordant with the VN test results. The low antigenic relatedness (ranging from 5.3–30% between Brazilian genotype BR-I and reference IBV serotypes of North America, Europe, and Asia) indicates that the BR-I genotype is a different serotype, referred to for the first time and hereafter as serotype BR-I.

RESEARCH HIGHLIGHTS

• Strains of the BR-I genotype presented robust antigenic and molecular similarity.

• BR-I strains evolved under purifying selection mode (negative pressure).

• The BR-I genotype originated in Brazil and dispersed to other countries.

• BR-I genotype viruses can be referred to as the BR-I serotype.

KEYWORDS:

• Infectious bronchitis virus
• BR-I serotype
• virus neutralization
• phylogenetic analysis
• selective pressure
• N-glycosylation
• recombination
• phylodynamics

Ethical statement

This study was approved by the Ethics Commission on Animal Use of the School of Veterinary Medicine, University of São Paulo (FMVZUSP), under CEUAVET protocol no. 5916141217.

Acknowledgements

The authors would like to thank the postgraduation students of the Laboratory of Avian Pathology, University of São Paulo, for their collaboration and Drs V. Palya and L. Sesti for providing the European antisera.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was financed in part by the CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior–Brasil)–Finance Code 001. A.J.P.F. is a recipient of CNPq (Conselho Nacional de Pesquisa e Desenvolvimento Tecnológico) fellowship 1D.