Amino acid changes in the variable region of VP2 in three infectious bursal disease viruses with different virulence, originating from a common ancestor.

ABSTRACT

An infectious bursal disease virus (IBDV), Hyd(C), from an outbreak was isolated and plaque-purified in BGM-70 cells. From the moderately virulent plaque-purified virus, two IBDVs with relatively high and low virulence were obtained by passaging the virus in specific pathogen free chickens and BGM-70 cells 10 and seven times, respectively. Comparison of amino acid sequences of the VP2 variable region of these viruses revealed that three amino acids at positions 279, 284 and 300 (Asp, Thr and Glu, respectively, in the plaque-purified virus) were changed. In in vitro- passaged virus, amino acid residues 279, 284 and 300 were Asn, Thr and Glu, whereas these were Asp, Ala and Gln in the in vivo -passaged virus. Change of residue 284 (Thr -->Ala) had a critical role in cell culture infectivity, whereas the change in residue 279 (Asp -->Asn) was associated with attenuation of the virus. No correlation could be observed between amino acid changes at position 300 and virulence or cell culture infectivity. Moreover, residue 330 (Arg) in heptapeptide motif SWSAR 330 GS was not found to be associated with the cell culture infectivity or virulence.