Abstract
Fowl typhoid (FT), a septicemic disease caused by Salmonella Gallinarum (SG), and infectious bronchitis (IB) are two economically important avian diseases that affect poultry industry worldwide. Herein, we exploited a live attenuated SG mutant, JOL967, to deliver spike (S) protein 1 of IB virus (V) to elicit protective immunity against both FT and IB in chickens. The codon optimized S1 nucleotide sequence was cloned in-frame into a prokaryotic constitutive expression vector, pJHL65. Subsequently, empty pJHL65 or recombinant pJHL65-S1 plasmid was electroporated into JOL967 and the resultant clones were designated as JOL2068 and JOL2077, respectively. Our results demonstrated that the chickens vaccinated once orally with JOL2077 elicited significantly (p < 0.05) higher IBV-specific humoral and cell-mediated immunity compared to JOL2068 and PBS control groups. Consequently, on challenge with the virulent IBV strain at 28th day post-vaccination, JOL2077 vaccinated birds displayed significantly (p < 0.05) lower inflammatory lesions in virus-targeted tissues compared to control groups. Furthermore, 33.3% (2 of 6) of birds vaccinated with JOL2077 vaccine had shown virus recovery from tracheal tissues compared to 100% (6 of 6) recovery obtained in both the control groups. Against wild-type SG lethal challenge, both JOL2077 and JOL2068 vaccinated groups exhibited only 10% mortality compared to 80% mortality observed in PBS control group. In conclusion, we show that JOL2077 can induce efficient IBV- and carrier-specific protective immunity and can act as a bivalent vaccine against FT and IB. Further studies are warranted to investigate the potential of JOL2077 vaccine in broiler and young layer birds.
Highlights
Infectious bronchitis virus (IBV), one of the prototype viruses of the Coronaviridae family, is an enveloped, single-stranded, positive-sense RNA virus that causes significant economic losses in poultry industry worldwide [1, 2]
The pJHL65-S1 gene construct was electroporated into JOL967 strain and the resultant clone was designated as JOL2077
Our results indicated that JOL2077 vaccinated chickens elicited significantly (p < 0.05) higher IBV-specific CD4+ T cell responses compared to the JOL2068 and the PBS control groups (Figure 3B)
Summary
Infectious bronchitis virus (IBV), one of the prototype viruses of the Coronaviridae family, is an enveloped, single-stranded, positive-sense RNA virus that causes significant economic losses in poultry industry worldwide [1, 2]. Inactivated IBV vaccines are safe, but relatively costlier and less effective than live attenuated vaccines, while use of live attenuated vaccines may result in the emergence of novel variants of the virus [10, 11]. The existence of more than 20 IBV serotypes with little cross protective immunity among vaccine strains results in poor efficacy of the currently available vaccines. The introduction and development of an effective and safe vaccine against each IBV serotype is not an economically viable option for the poultry industry. Novel approaches should be devised that are egg independent and cost-effective, but easy to amplify and can provide efficient protection against the circulating IBV strains
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