Infectious bursal disease virus recovery from Vero cells transfected with RNA transcripts is enhanced by expression of the structural proteins in trans

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Abstract
Positive sense RNA transcripts of infectious bursal disease (IBD) virus genome segments A and B have previously been shown to be infectious [10]. In this study we demonstrate that recovery of IBD virus from the transfection of Vero cells with positive sense RNA transcripts of genome segments A and B was enhanced by expression of the viral structural proteins VP2 with VP3 or by expression of viral polyprotein VP243 from DNA plasmids in trans. Expression of individual viral proteins VP2, VP3, or VP4 alone from DNA plasmids did not enhance IBD virus recovery. Earliest virus recovery from transfection of positive sense RNA transcripts of genomic segments A and B was at 36 h and mean titers were 101.8 pfu/ml. IBD virus was recovered 6 hours after transfection in cells concurrently expressing either VP2 with VP3 or VP243 and mean titers were 108.5 pfu/ml or 109.2 pfu/ml, respectively. Likewise, expression of the viral polyprotein from DNA plasmid increased the permissiveness of Vero cells for infection with non-culture adapted IBD virus. The titer of recovered non-culture adapted virus from 103.3 pfu/ml to 1010.3 pfu/ml with expression of the viral polyprotein. This report is the first to describe a reverse genetics model for IBD virus with high efficiency of virus recovery for non-culture adapted strains.