[Construction and immunological characterization of recombinant Marek's disease virus expressing IBDV VP2 fusion...

A transfer plasmid vector pUC18-US10-VP2 was first constructed by inserting the gene of the enhancer green fluorescent protein(eGFP) fused to the VP2 gene of very virulent Infectious bursal disease virus (IBDV) JS strain into the US10 fragment of the Marek's disease virus (MDV) CV1988/Rispens. The recombinant virus, designated as rMDV, was developed by co-transfecting CEF with the transfer plasmid vector and simultaneously infecting with the CVI988/Rispens virus. The PCR and IFA results indicated that the rMDV is stable after 31 passages. Chickens vaccinated with rMDV were protected from challenge with 100LD50 of IBDV JS. The protection ratio of the chickens vaccinated with the 1000PFU, 2000PFU, 5000PFU of the rMDV were 50%, 60%, and 80% respectively. It is interesting that the average histopathology BF lesion scores of chicken group immunized with 5000PFU of rMDV by one-time vaccination was close to that of chicken group vaccinated with IBDV live vaccine NF8 strain for twice (2.0/1.5). There is no difference in protection between the groups (P > 0.05) but significent difference between groups immunized with 5000 PFU of rMDV and with normal MDV. This demonstrated that rMDV expressing VP2 fusion protein was effective vaccine against IBDV in SPF chickens.