Genotyping of the infectious bursal disease virus (IBDV) based on the hypervariable region of the vp2 gene in broiler chickens from the State of Rio de Janeiro, Brazil

ABSTRACT: Infectious bursal disease virus (IBDV) causes immunosuppression in broilers by affecting the bursa of Fabricius. IBDV strains were classified into seven genogroups based on the amino acid composition of the hypervariable region of the VP2 capsid protein. This study aimed to detect and genotype IBDV strains in bursal samples from broilers in Rio de Janeiro and evaluate the genetic variability of the vp2 gene. Sixty-five bursal tissue samples from broilers suspected to have IBD were collected from four farms in Rio de Janeiro and stored in RNAlater. RNA was extracted using TRIzol reagent, and genotyping was performed using RT-qPCR. The VP2 hypervariable region was amplified using conventional PCR, purified, and sequenced. Phylogenetic analysis was conducted using the maximum likelihood method with the Kimura 2-parameter substitution model. IBDV was detected in 75.38% (49/65) of the samples, with 8.16% (4/49) classified as very virulent (vvIBDV) and 91.84% (45/49) as non-vvIBDV strains. This study seems to be the first report of G-3 infection in the state of Rio de Janeiro. Sequence comparison identified multiple missense mutations, including 20 in genogroup 4 and eight in genogroup 3, relative to the reference strain Edgar-USA. The genetic distances among the isolates suggest potential viral evolution and adaptation. These findings highlight the genetic diversity of IBDV in this region and reinforce the importance of continuous molecular surveillance of the virus. The detection of vvIBDV in a previously unreported area underscores the need for monitoring strategies to mitigate the impact of emerging strains on poultry production. Further studies focusing on antigenic variation and vaccine efficacy are essential to ensure effective control of IBDV.