Abstract
Viral vectored vaccines are desirable alternatives for conventional infectious bronchitis virus (IBV) vaccines. We have recently shown that a recombinant Newcastle disease virus (rNDV) strain LaSota expressing the spike (S) protein of IBV strain Mass-41 (rLaSota/IBV-S) was a promising vaccine candidate for IBV. Here we evaluated a novel chimeric rNDV/avian paramyxovirus serotype 2 (rNDV/APMV-2) as a vaccine vector against IBV. The rNDV/APMV-2 vector was chosen because it is much safer than the rNDV strain LaSota vector, particularly for young chicks and chicken embryos. In order to determine the effectiveness of this vector, a recombinant rNDV/APMV-2 expressing the S protein of IBV strain Mass-41 (rNDV/APMV-2/IBV-S) was constructed. The protective efficacy of this vector vaccine was compared to that of the rNDV vector vaccine. In one study, groups of one-day-old specific-pathogenic-free (SPF) chickens were immunized with rLaSota/IBV-S and rNDV/APMV-2/IBV-S and challenged four weeks later with the homologous highly virulent IBV strain Mass-41. In another study, groups of broiler chickens were single (at day one or three weeks of age) or prime-boost (prime at day one and boost at three weeks of age) immunized with rLaSota/IBV-S and/or rNDV-APMV-2/IBV-S. At weeks six of age, chickens were challenged with a highly virulent IBV strain Mass-41. Our challenge study showed that novel rNDV/APMV-2/IBV-S provided similar protection as rLaSota/IBV-S in SPF chickens. However, compared to prime-boost immunization of chickens with chimeric rNDV/APMV-2, rLaSota/IBV-S and/or a live IBV vaccine, single immunization of chickens with rLaSota/IBV-S, or live IBV vaccine provided better protection against IBV. In conclusion, we have developed the novel rNDV/APMV-2 vector expressing S protein of IBV that can be a safer vaccine against IB in chickens. Our results also suggest a single immunization with a LaSota vectored IBV vaccine candidate provides better protection than prime-boost immunization regimens.
Highlights
Infectious bronchitis (IB) is a highly contagious viral disease of poultry [1]
The transcription cassette containing the S gene of Infectious bronchitis virus (IBV) was inserted between the P and M genes in two individual plasmids containing cDNA of the full length antigenomic RNA of Newcastle disease virus (NDV)-avian paramyxovirus (APMV)-2 or LaSota-527. recombinant Newcastle disease virus (rNDV)-APMV-2 expressing IBV S protein and rAPMV-1 strain LaSota (rLaSota)-527 expressing IBV S protein were recovered from cDNAs successfully
The plaque morphology assay showed that either rNDV-APMV-2 or rNDV-APMV-2/IBV-S did not form visible plaques in DF1 cells under Dulbecco’s minimal essential medium (DMEM) containing 0.8% methyl cellulose over layer (Figure 1C)
Summary
Infectious bronchitis (IB) is a highly contagious viral disease of poultry [1]. It is predominantly a respiratory disease, but it can affect renal and reproductive tracts. Respiratory distress, poor carcass weight, substandard egg quality, and decreased egg production resulting from IB cause huge economic losses for the poultry industry worldwide [1,2]. Infectious bronchitis virus (IBV) is a member of the family Coronaviridae. The genome of IBV is a non-segmented, positive-strand RNA of about 27.6 kilobase (kb) in length. The genome consists of five basic and four accessory genes in the order 50-leader-replicase-UTR-S(spike)-3a,3b-M(membrane)-E(envelope)
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