SEQUENCE COMPARISONS OF THE VARIABLE VP2-REGION OF 8 INFECTIOUS BURSAL-DISEASE-VIRUS ISOLATES

The VP2 gene is part of the genomic segment A of infectious bursal dis ease virus (IBDV). It has been identified as the major host-protective antigen of IBDV and is known to contain conformationally dependent pr otective epitopes., A 643-base pair segment covering the hypervariable region of this gene from three recent serologic variant IBDV isolates from tile southeastern United States, two variants from the Delmarva Peninsula, and three serologic standard viruses were amplified and seq uenced using the reverse transcription polymerase chain reaction and c ycle sequencing techniques. This was done to determine the molecular s imilarity among isolates that differ antigenically and pathologically. Sequence analysis suggested that rile Arkansas (Ark) and Mississippi (Miss) isolates evolved closely and separately from the Delmarva varia nts (GLS and DELE), in contrast ro the other southeastern variant Geor gia (Ga), which is more closely related (98.32%) to Delaware E. (DELE) . All variants, except for Miss, underwent a shift in amino acid numbe r 222 from proline to threonine. The sequence of Univax ED virus, a co mmercially available intermediate vaccine, was markedly different, evo lving from a separate lineage than the others. Restriction enzyme site s could differentiate most isolates. Except for Miss, variants do not have EcoRII site at the larger hydrophilic domain. All variants lost t heir HaeIII, StuI, and StyI cutting sites with a change in base number 856. The TaqI site is in DELE, whereas tile SpeI sire is absent in th e standard vaccine viruses. The SWASASGS heptapeptide is conserved in all virulent viruses, including APHIS, bur not in the attenuated (Univ ax ED and Bursa Vac 3) and published (D78 and PBG38) vaccines.