Protective Effect of In ovo Vaccination with IBV-Spike-Recombinant DNA and Chicken Interferon as an Adjuvant

Infectious Bronchitis Virus (IBV) can cause high mortality, poor weight gain and low feed efficiency of infected chickens, which leading to considerable economic losses to the poultry industry. In this study, a plasmid DNA pTracer-CVM2-IBVS (abbr: pCMV-S) that expresses the immunogenic S glycoprotein genes of IBV serotype Massachusetts 41 was inoculated in ovo into 18-days-old embryonating Specific-Pathogen- Free (SPF) chicken eggs as a vaccine. Recombinant chicken interferon type I alpha (rChlFN-a) was added as an adjuvant to enhance the immunogenicity of the vaccine. After hatch, birds were challenged at 4 weeks of age with a homologous pathogenic Massachusetts 41 field type IBV. Birds receiving a single dose of pCMV-S vaccine in ovo showed mild clinical signs and were protected at the level of 66%, whereas groups receiving a combination of the pCMV-S with 2000 IU or 500 IU of rChlFN-a showed protection at the level of 83 and 89% respectively. The pCMV-S + 500 IU rChlFN-a vaccinated group, when boosted with a live attenuated commercial IBV vaccine at 2 weeks of age indicated a significant protection (> 92 %) against IBV challenge. At 5 days post challenge, no clinical signs were seen from the birds vaccinated with 5 ug of pCMV- +500 IU rChlFN and the birds received booster with commercial IBV vaccine. RT-PCR based diagnostic test indicated detecting IBV infection was reduced in birds received pCMV-S with 2000 IU or 500 IU of rCHIFN-a. This study indicates that the application of rChlFN-a as an adjuvant with pTracer-CMV-IBVS vaccine expressing S glycoprotein gene was somewhat effective in controlling IBV infection. Additionally an increase in protection against the homologous IBV challenge was observed in birds boosted with the live attenuated IBV commercial vaccine.