Title: Infectious bronchitis virus S2 expressed from recombinant virus confers broad protection against challenge Authors
|Toro, Haroldo -|
|Zhao, Wei -|
|Breedlove, Cassandra -|
|Zhang, Zhenyu -|
|Van Santen, Vicky -|
Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2013
Publication Date: March 1, 2014
Citation: Toro, H., Zhao, W., Breedlove, C., Zhang, Z., van Santen, V., Yu, Q. 2014. Infectious bronchitis virus S2 expressed from recombinant virus confers broad protection against challenge. Avian Diseases. 58(1):83-89. Interpretive Summary: Infectious bronchitis (IB), caused by infectious bronchitis virus (IBV) infection, is one of the most prevalent avian diseases in the world’s poultry industry. Effective control of IBV is particularly difficult due to genotype/phenotype diversity and continuing evolution of the virus. In the present study, we developed recombinant Newcastle disease virus (NDV) LaSota (rLS) expressing a distinct spike (S) protein gene of IBV (rLS/IBV.S2). Chickens were primed with rLS/IBV.S2 and boosted with commercial Mass-type vaccine, then challenged with heterotypic virulent Arkansas type IBV. The results showed that this recombinant vaccine prime/boost technology confers cross-protection among different IBV strains. We also experimentally demonstrated that the recombinant construct maintains the biological properties of the parental NDV and provides complete protection against challenge with velogenic NDV.
Technical Abstract: We developed recombinant Newcastle disease virus (NDV) LaSota (rLS) expressing the IBV S2 gene (rLS/IBV.S2). The recombinant virus showed reduced pathogenicity compared to the parental LaSota strain but effectively elicited hemagglutination inhibition antibodies and protected chickens against lethal challenge with virulent NDV/CA02. IBV heterotypic protection was assessed using a prime/boost approach with a commercially available attenuated IBV Massachusetts (Mass)-type vaccine. Specific pathogen free chickens primed ocularly with rLS/IBV.S2 at 4 days of age and boosted with Mass at 18 days of age were completely protected against challenge at 41 days of age with a virulent Ark-type strain. In a 2nd experiment we compared protection conferred by priming with rLS/IBV.S2 and boosting with Mass (rLS/IBV.S2+Mass) versus priming and boosting with Mass (Mass+Mass). We also modified the timing of vaccination to prime at 1 day of age and boost at 12 days of age. Challenge with virulent Ark was performed at 21 days of age. Based on clinical signs both groups seemed equally protected against challenge compared to unvaccinated/challenged chickens. Results of viral load in lachrymal fluids of birds receiving rLS/IBV.S2+Mass showed a clear tendency of improved protection compared to Mass+Mass but the difference did not achieve statistical significance. A significant difference (P<0.05) was determined between these groups regarding incidence of challenge IBV RNA in the trachea; viral RNA was detected in 50% of rLS/IBV.S2+Mass vaccinated chickens while chickens vaccinated with Mass+Mass and unvaccinated/challenged controls showed 84% and 90% incidence of IBV RNA in the trachea respectively. These results demonstrate that overexposing the IBV S2 to the chicken immune system by means of a vectored vaccine, followed by boost with whole virus, protects chickens against IBV showing dissimilar S1.