Continuous circulation and mutation at the hypervariable region of the VP2 gene of very virulent infectious bursal disease virus in Nigeria

Abstract

Infectious bursal disease (IBD) is a highly contagious viral disease of poultry with huge economic consequences. First reported in Nigeria in 1973, the disease has since become endemic across the country. Inspite of routine vaccine administration, outbreaks are frequently reported in vaccinated flocks which questions the effectiveness of the vaccine to confer adequate protection against the circulating strains of the virus. In this study, suspected IBD outbreaks from 9 poultry farms spanning 2015 – 2016 were investigated. The hypervariable region (HVR) of the VP2 gene of infectious bursal disease virus (IBDV) from these outbreaks was sequenced. Based on the phylogenetic tree and deduced amino acid sequences, the viruses clustered with African very virulent (vv) types (VV2-1) with markers typical for vvIBDV at positions 222A, 242I, 256I, 294I and 299S. Also, unique substitutions were identified at the hydrophilic peak A (215Q→P) and minor peak 2 (280N→Y) in addition to that previously unreported at position 308I→L. These results demonstrate continuous circulation and mutations at the HVR of the VP2 which underscores the need for constant monitoring of IBDV in Nigerian poultry. Further study is required to establish the biological function(s) of these mutations on the pathogenicity and antigenicity of the virus.

Keywords: very virulent infectious bursal disease virus, VP2 gene, mutation, poultry, Nigeria