Sequence analysis of VP2 hypervariable region of the field isolates of infectious bursal disease viruses from southern region of India

VP2 gene sequencing based Geno-grouping of infectious bursal disease viruses isolated from Gujarat and Maharashtra state (India)

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), has recently been reported in chickens vaccinated with classical or intermediate types of vaccines from various regions of India due to the emergence of novel very virulent strains of infectious bursal disease virus (vvIBDV). In the present study, suspected samples of IBD were collected from poultry flocks of districts of Gujarat and Nagpur (Maharashtra), identified using PCR and grouped as per traditional and new genogrouping pattern. Out of 54 bursa samples, 21 (38.89%) yielded the expected amplicon of 743 bp (701-1444 bp), and were found positive for IBDV. Among these 21 positive flocks, 11 (52.38%) were already vaccinated. Upon nucleotide sequencing of amplicon and its deduction into amino acids, it was found that all the sequences of present study were related to vvIBDV according to old classification pattern. Considering the new genogrouping pattern, nine and four sequences of this study fell within G3a and G3b lineage, respectively. These sequences revealed important differences at key amino acid positions with respect to classical (G1 genogroup), variant (G2 genogroup) type of IBDV and classical vaccines. Further divergence from prototypic vvIBDV strains was revealed as, D-N at 212 position (N = 9) and 279 position (N = 1). In sequences from Maharashtra (group 2 of G3a lineage), occurrence of V instead of P/T/A at 222 position was recorded as a novel and conspicuous substitution in the immunodominant peak A of VP2 hypervariable region. Additional changes at 270 (3 sequences) and 272 positions (4 sequences) could be attributed to reverse mutation or recombination with vaccine strains. In conclusion, both point mutation and genetic reassortment with intermediate type of vaccines were found to be responsible for generation of novel vvIBDV strains in this area which belonged to G3a and G3b genogroups.

Identification and genetic analysis of infectious bursal disease viruses from field outbreaks in Kerala, India

Recurrent infectious bursal disease (IBD) outbreaks were reported in different regions of Kerala, India. This paper reports the comparative genetic analysis of the hypervariable region of the VP2 gene of IBD virus isolates from the field outbreaks in Kerala. In phylogenetic analysis, the obtained field isolates fall into genogroup 1 and 3. In genogroup 3, all vvIBDV isolates shared a common ancestor with other south Indian isolates but isolates 9/CVASP/IBDV, 10/CVASP/IBDV, 12/CVASP/IBDV, 14/CVASP/IBDV and 17/CVASP/IBDV are most recently evolved and are diverged from the south Indian isolates. The amino acid sequence of 22 isolates was analysed, out of which 18 had conserved amino acids which were characteristic of vvIBDV. All the vvIBDV isolates obtained in the study had phenylalanine and valine at the position 240 and 294, respectively, similar to recently evolved Indian IBDV isolate (MDI14). But we observed T269A and S299N mutations in the isolate 6/CVASP/IBDV, and it is the first report of such mutations at these positions in India IBDV isolates. The isolate 11/CVASP/IBDV had a unique mutation of V225A which is not yet reported in IBDV isolates. Two isolates (15/CVASP/IBDV and 18/CVASP/IBDV) were 100% amino acid similar to intermediate plus vaccine strain. The isolates 8/CVASP/IBDV/VP2 and 19/CVASP/IBDV had amino acids unique for the intermediate vaccine with mutations observed at H253Q and V256I in 19/CVASP/IBDV, T270A and novel mutation N279Y in isolate 8/CVASP/IBDV. These two isolates had non-virulent classical heptapeptide sequence 'SWSARGS'; nevertheless, they produce field outbreaks of IBD. This is the first report of genetic characterisation of IBDV in Kerala, India.

Molecular characterization of field isolates of infectious bursal disease virus from three decades, 1987-2018, reveals a distinct genotypic subgroup in Vietnam

The complete nucleotide sequence of the viral protein 2 (VP2) ORF was determined for 26 Vietnamese infectious bursal disease isolates collected from clinical outbreaks in vaccinated flocks from 1987 to 2018 and two commercial vaccine specimens. These sequences were compared for molecular classification with 42 reference strains representing all four main classes of serotype 1, including very virulent (vvIBDV), classical (cvIBDV), antigenic variant (avIBDV) and attenuated (atIBDV) strains, and serotype 2 strains. Amino acids at nine key positions in the VP2-HVR in 20 Vietnamese isolates, A222, I242, Q253, I256, D279, A284, I294, S299, A329, which are typical of the vvIBDV class, were found to be identical in all of the isolates. Eighteen of these isolates had a unique change at residue 212 (D212N) located in the P_AB loop. Phylogenetic analysis revealed a distinct lineage/subclade with strong nodal support (96%) that included recent Chinese IBDV strains that were distinct from typical vvIBDVs. Six isolates contained the amino acid substitutions P222, V242, Q253, V256, D279, A284, I294, N299, A329, which are present in two vaccine strains derived from strain 2512 and these isolates were also closely related to the classical virulent STC strain. Data from this study show that there is considerable genetic diversity among vvIBDVs, which vary according to geographic region. Antigenic drift and differences in genetic characteristics between virulent strains and IBDV vaccine strains may be the cause of vaccine failure. Better antigenic matching of vaccines to the strains circulating in Vietnam is therefore required.