Recombinant canarypox virus expressing the VP2 protein of infectious bursal disease virus induces protection in vaccinated SPF chickens

Abstract

Infectious bursal disease virus (IBDV) is the causative agent of an immunosuppressive disease that causes important economic losses to the poultry industry. Current attenuated viral vaccines pose drawbacks and risks and thus the development of safe and effective novel vaccines becomes indispensable. The efficacy of canarypox virus (CNPV) as vector to express heterologous antigens from mammalian pathogens has been well established; however, there is little data about its evaluation as immunogen for chickens. In this work we evaluated both the non-replicative status and the protective efficacy of a recombinant CNPV (CN048-VP2) expressing the viral protein 2 of IBDV.We observed that CN048-VP2 developed nodular lesions smaller than fowl pox vaccine when applied via wing web and the viral DNA was only detectable at the site of inoculation for 24 h after intramuscular injection. To evaluate the efficacy induced by CNPV-based vector one-day old specific pathogen free chickens were subcutaneously immunized with a single dose of 106 plaque forming units (PFU) of CN048-VP2 or CNPV. After 50 days, the chickens were orally infected with an IBDV strain of intermediate virulence and 5 days after the infection the bursae were inspected. The bursae of CN048-VP2-vaccinated birds showed low levels of mononuclear cell infiltration and displayed apparently normal histology. Furthermore, the challenge virus was undetectable in the bursae of this group. Conversely, the bursae of CNPV-vaccinated birds displayed the characteristic histopathological lesions and high IBDV titers.Taken together, these results suggest the CN048-VP2 vector has a promising future as vaccine candidate against IBDV.