Herpesvirus of turkey recombinant viruses expressing infectious bursal disease virus (IBDV) VP2 immunogen induce protection against an IBDV virulent challenge in chickens.
Two recombinant turkey herpesviruses (HVT) expressing the VP2 protein of infectious bursal disease virus (IBDV) were constructed: vHVT001 and vHVT002. The VP2 open reading frame was inserted at the locus of the small subunit of ribonucleotide reductase gene (HSV-1 UL40 homologue) without exogenous promoter in vHVT001 and at the locus of gI gene (HSV-1 US7 homologue) under the control of the human cytomegalovirus immediate-early promoter in vHVT002. The isolation of these recombinant viruses indicated that the deleted genes were not required for replication of HVT in chick embryo fibroblasts. Efficacy of these recombinant viruses against IBDV strain 52/70 and Marek's disease virus (MDV strain RB1B) virulent challenges was examined in chickens vaccinated at 1 day of age. After IBDV challenge, vHVT002 showed good protection against mortality and bursal gross lesions: 100% with 105 PFU dose and 60% with 104 PFU dose; in contrast, only a weak protection was found after vaccination with vHVT001. Protection levels against MDV challenge obtained with vHVT001 and vHVT002 were low (around 10%) compared to that induced by the parental HVT (84%). In spite of the low protection level against MDV, this is the first report which describes induction of full protection against IBDV with a single inoculation of a recombinant virus.