Sequence Comparisons of the Variable VP2 Region of Eight Infectious Bursal Disease Virus Isolates

Abstract

The VP2 gene is part of the genomic segment A of infectious bursal disease virus (IBDV). It has been identified as the major host-protective antigen of IBDV and is known to contain conformationally dependent protective epitopes. A 643-base pair segment covering the hypervariable region of this gene from three recent serologic variant IBDV isolates from the southeastern United States, two variants from the Delmarva Peninsula, and three serologic standard viruses were amplified and sequenced using the reverse transcription polymerase chain reaction and cycle sequencing techniques. This was done to determine the molecular similarity among isolates that differ antigenically and pathologically. Sequence analysis suggested that the Arkansas (Ark) and Mississippi (Miss) isolates evolved closely and separately from the Delmarva variants (GLS and DELE), in contrast to the other southeastern variant Georgia (Ga), which is more closely related (98.32%) to Delaware E (DELE). All variants, except for Miss, underwent a shift in amino acid number 222 from proline to threonine. The sequence of Univax BD virus, a commercially available intermediate vaccine, was markedly different, evolving from a separate lineage than the others. Restriction enzyme sites could differentiate most isolates. Except for Miss, variants do not have EcoRII site at the larger hydrophilic domain. All variants lost their HaeIII, StuI, and StyI cutting sites with a change in base number 856. The TaqI site is in DELE, whereas the SpeI site is absent in the standard vaccine viruses. The SWASASGS heptapeptide is conserved in all virulent viruses, including APHIS, but not in the attenuated (Univax BD and Bursa Vac 3) and published (D78 and PBG98) vaccines.

Sequence Comparison of the VP2 Variable Region of Infectious Bursal Disease Virus Isolates from Vietnam.

“…Among these proteins, the structural protein VP2 has been identified as the major host-protective immunogen of IBDV [2,4]. Sequence analysis of VP2 genes of various isolates showed that changes in the center of VP2 account for antigenic or pathogenic variations of IBDV [3,5,7,9,10,20,27,30,31].…”

“…1, the Vietnamese virulent strain 17a and the classical strain 52/70 had only one amino acid substitution in the hydrophobic matrix (residue 254, serine in 17a and glycine in 52/70). Dormitorio et al [9] reported the only change that could distinguish the variants from the standard isolates is in residue 254, which changed from glycine in the standard isolates to serine in the variants. Further studies on antigenicity of this Vietnamese strain and the others are necessary to elucidate the epidemiology of IBDV in Vietnam.…”

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

“…The trend of mutation is followed naturally in the existing genetic pool of Indo-Pak region [8]. 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.…”

“…Selected sequences were aligned by Neighbour-Joining (NJ) Method. This information provides many important aspects [2,9,10]. Topologically, the phylogenetic tree revealed that IBDVs separated into three main groups, namely vvIBD viruses, classic/variant viruses and attenuated/vaccine strains.…”

“…Under high selection pressure in immune populations there is emergence of new viral strains in targeted poultry flock. VP2, structural protein has a major virus neutralizing conformational epitopes in hypervariable region [8][9][10]. Antigenicity and virulence of the IBDV has been studied extensively on the genetic basis to control IBD [11][12][13][14].…”