Abstract
Infectious bronchitis virus (IBV) causes a major disease problem for the poultry industry worldwide. The currently used live-attenuated vaccines have the tendency to mutate and/or recombine with circulating field strains resulting in the emergence of vaccine-derived variant viruses. In order to circumvent these issues, and to develop a vaccine that is more relevant to Egypt and its neighboring countries, a recombinant avirulent Newcastle disease virus (rNDV) strain LaSota was constructed to express the codon-optimized S glycoprotein of the Egyptian IBV variant strain IBV/Ck/EG/CU/4/2014 belonging to GI-23 lineage, that is prevalent in Egypt and in the Middle East. A wild type and two modified versions of the IBV S protein were expressed individually by rNDV. A high level of S protein expression was detected in vitro by Western blot and immunofluorescence analyses. All rNDV-vectored IBV vaccine candidates were genetically stable, slightly attenuated and showed growth patterns comparable to that of parental rLaSota virus. Single-dose vaccination of 1-day-old SPF White Leghorn chicks with the rNDVs expressing IBV S protein provided significant protection against clinical disease after IBV challenge but did not show reduction in tracheal viral shedding. Single-dose vaccination also provided complete protection against virulent NDV challenge. However, prime-boost vaccination using rNDV expressing the wild type IBV S protein provided better protection, after IBV challenge, against clinical signs and significantly reduced tracheal viral shedding. These results indicate that the NDV-vectored IBV vaccines are promising bivalent vaccine candidates to control both infectious bronchitis and Newcastle disease in Egypt.
Highlights
Infectious bronchitis (IB) is an acute, highly contagious viral disease of chickens
Construction of recombinant avirulent Newcastle disease virus (rNDV) and analysis of Infectious bronchitis virus (IBV) S protein expression All the three forms of IBV S gene were inserted into the full-length cDNA clone of Newcastle disease virus (NDV) strain LaSota between the P and M genes, and their corresponding recombinant viruses, rLaSota/wt.S, rLaSota/S(Y1145A) + Fct12 and rLaSota/SΔct + Fct12, were successfully rescued
Immunofluorescence analysis showed only intracellular expression of IBV S protein in DF-1 cells infected with rLaSota/ wt.S; whereas, both intracellular and surface expression of IBV S protein were observed in cells infected with rLaSota/S(Y1145A) + Fct12 and rLaSota/SΔct + Fct12
Summary
Infectious bronchitis (IB) is an acute, highly contagious viral disease of chickens. IB affects chickens of all ages and based on the organ system affected the disease is manifested in three major clinical forms—respiratory, renal and reproductive. Infectious bronchitis virus (IBV) is a member of the genus Gammacoronavirus in the family Coronaviridae. The viral genome is a single-stranded, positive-sense RNA of about 27.6 Kb. The S protein of IBV is heavily glycosylated and plays a major role in eliciting protective immune responses. The S protein of IBV is heavily glycosylated and plays a major role in eliciting protective immune responses It is present as trimers on the surface of the virion and contains conformation dependent epitopes [4].
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