Molecular characterization of infectious bursal disease viruses from Pakistan

Abstract

Since the first report of infectious bursal disease in Pakistan in 1987, outbreaks have been common even in vaccinated flocks. Despite appropriate administration of vaccines, concerns arise if the circulating strains are different from the ones used in the vaccine. Here, we sequenced the hypervariable region (HVR) of the VP2 gene of circulating strains of infectious bursal disease virus (IBDV) originating from outbreaks (n = 4) in broiler flocks in Pakistan. Nucleotide sequencing followed by phylogeny and deduced amino acid sequence analysis showed the circulating strains to be very virulent (vv) and identified characteristic residues at position 222 (A), 242 (I), 256 (I), 294 (I) and 299 (S). In addition, a substitution at positions 221 (Q→H) was found to be exclusive to Pakistani strains in our analysis, although a larger dataset is required to confirm this finding. Compared to vaccine strains that are commonly used in Pakistan, substitution mutations were found at key amino acid positions in VP2 that may be responsible for potential changes in neutralization epitopes and vaccine failure.

Molecular Characterization of Infectious Bursal Disease Virus From Commercial Poultry in Pakistan

“…Some of US variant and French vvIBDVs matched the similar ongoing change [9,41]. Shabir and co-workers reported that Histidine, amino acid (H) is located at position 221 [33] is characteristic for Pakistani strains. Present studies differ from reported information.…”

“…The research analysis showed that there is wide difference between present circulating IBD viral load and the attenuated viruses, incorporated in commercial vaccines. The study was designed to characterize the existing IBDV strains [32,33] responsible for causing economic losses.…”

Sequence and Structural Analysis of Synthetic VP2 Antigenic Protein as a Subunit Vaccine Candidate against Very Virulent Strains of Infectious Bursal Disease Virus

“…Multiple sequence alignment of synthetic VP2 hypervariable region (HVR) with those of vvIBDV strains representing various regions of the world together with two vaccine strains revealed the same epitopic sites in HVR of synthetic VP2 gene as documented in the HVR of vvIBDVs from various continents of the world. HVR consists of neutralizing antigens and is a major domain in VP2 protein (Shabbir et al, 2016). The synthetic VP2 hyper variable region, 145 amino acids (aa) in length covering positions 206-350 of the protein, exposed aa residue A at position 222, I at 242, 256, 294 and S at 299.…”

“…Strains belonging to serotype I specifically infect the chickens whereas IBDV strains in serotype II have more prevalence in turkeys (Reddy et al, 2017). Serotype I of IBDV includes three pathotypes viz classical virulent (cv) viruses, antigenic variants and very virulent (vv) IBDVs (Shabbir et al, 2016). Chicken bearing bursal damage due to infection by classical virulent strains showed 20-30% mortality (Lukert and Saif, 2003).…”

“…The antigenicity of VP2 protein is conformation-dependent because loss of cross-reactivity of neutralizing antibodies has been depicted in Western blots against denatured VP2 (Schnitzler et al, 1993). A 145 amino acid (aa) long hyper-variable region (HVR) of VP2 protein is documented as the major antigenic site (Shabbir et al, 2016). This hyper-variable region contributes towards molecular typing of diverse IBDV isolates as it varies greatly among the pathotypes of serotype I and also between two IBDV serotypes.…”