A Recombinant La Sota Vaccine Strain Expressing Multiple Epitopes of Infectious Bronchitis Virus (IBV) Protects Specific Pathogen-Free (SPF) Chickens against IBV and NDV Challenges.

Tan Tan,Meng Meng,Qiu Qiu,Shi Shi,Song Song,Wen Wen,Sun Sun,Shao Shao,Liao Liao,Yuan Yuan,Liu Liu,Ding Ding

doi:10.3390/vaccines7040170

Abstract

Infectious bronchitis (IB) and Newcastle disease (ND) are two major infectious diseases that are a threat to the domestic poultry industry. In this study, we successfully generated a recombinant LaSota candidate vaccine strain, rNDV-IBV-T/B, which expresses a short, synthetic, previously identified IBV S1 multi-epitope cassette using the reverse genetic system. The recombinant virus was propagated in nine-day-old embryonated chicken eggs for 20 passages and genetic stability was confirmed by whole genome DNA sequencing. The recombinant virus had a hemagglutination (HA) titer of 210, mean death time (MDT) of 118 hours, and intracerebral pathogenicity index (ICPI) of 0.05. None of these were significantly different from the parental Newcastle disease virus (NDV) LaSota strain (p > 0.05). Vaccination of white leghorn chickens at one day of age with 106 EID50 rNDV-IBV-T/B provided 90% protection against virulent IBV M41 challenge at three weeks of age, which was significantly higher than the protection of the control group vaccinated with phosphate-buffered saline (PBS) (p < 0.05). The ciliostasis scores of rNDV-IBV-T/B-vaccinated and LaSota-vaccinated groups were 4.2 and 37.6, respectively, which indicated that rNDV-IBV-T/B vaccination reduced the pathogenicity of IBV toward the trachea. Furthermore, real-time RT-PCR assay showed that the rNDV-IBV-T/B vaccination resulted in low levels of viral load (647.80 ± 49.65 RNA copies) in the trachea four days post-challenge, which is significantly lower than groups vaccinated with PBS (8591.25 ± 311.10 RNA copies) or LaSota (7742.60 ± 298.50 RNA copies) (p < 0.05). Meanwhile, the same dose of rNDV-IBV-T/B vaccination provided complete protection against velogenic NDV F48E9 challenge. These results demonstrate that the rNDV-IBV-T/B strain is a promising vaccine candidate to control both IB and ND simultaneously. Furthermore, epitope-based live vector vaccines provide an alternative strategy for the development of cost-effective and, broadly, cross-protective vaccines.

Highlights

Avian infectious bronchitis (IB) is an acute and highly contagious viral respiratory disease of chickens
Infectious bronchitis (IB) is caused by the infectious bronchitis virus (IBV) which belongs to the order Nidovirales, family
Novel serotype and variant IBV have emerged due to rapid mutation rates, viral recombination, and host selection pressure, which have resulted in IB prevention becoming a global challenge [11,12]

Summary

Introduction

Avian infectious bronchitis (IB) is an acute and highly contagious viral respiratory disease of chickens. Novel serotype and variant IBV have emerged due to rapid mutation rates, viral recombination, and host selection pressure, which have resulted in IB prevention becoming a global challenge [11,12]. Vaccination is the best method to control the disease, and the current widely used commercial IBV vaccines are live-attenuated or inactivated viruses with adjuvants derived from classical or variant serotypes [13], live-attenuated IBV vaccine strains have some limitations, including genetic instability, reversion to virulence, and recombination between vaccine and wild-type viruses [14]. Chicken flocks suffer co-infection with IBV and avian orthoavulavirus-1 (AOAV-1), which is a member of the genus

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