Development of Vaccines for Poultry Against H5 Avian Influenza Based on Turkey Herpesvirus Vector

Avian influenza (AI) remains a major threat to public health as well as to the poultry industry. AI vaccines are considered a suitable tool to support AI control programs in combination with other control measures such as good biosecurity and monitoring programs. We constructed recombinant turkey herpesvirus (HVT) vector vaccines expressing the hemagglutinin gene of AI virus H5 subtype (rHVT‐H5) and evaluated their characteristics and efficacy against AI. We found that the cytomegalovirus (CMV) promoter is the most suitable for expression of the hemagglutinin gene among three promoters we evaluated. The rHVT‐H5 vaccine did not cause any adverse reactions and did not revert to virulence after passages in chicken. Finally, efficacy of the rHVT‐H5 vaccine was evaluated. We demonstrated that it provided protection against diverse AI H5 viruses belonging to different clades and reduced virus shedding from the challenged chicken. We also proved that efficacy provided by the rHVT‐H5 vaccine was not significantly affected by presence of maternally derived antibodies (MDA) against AI virus. Furthermore, the rHVT‐H5 vaccine could be applicable to the differentiating infected from vaccinated animals (DIVA) strategy. In summary, we successfully developed a HVT vector AI vaccine that possesses features that could be beneficial to AI control

Serological Evaluation of Turkey Herpesvirus Vector Vaccines Expressing the Hemagglutinin Gene of Avian Influenza Virus H5 Subtype under Three Different Promoters

Marek’s disease virus, including turkey herpesvirus (HVT), have been utilized as vectors to express foreign antigen genes and induce immunity against the antigens in chickens. Selection of promoters in developing such vector vaccines is one of the most important factors influencing efficacy of vector vaccines. In this study, in order to find a suitable promoter for expressing the hemagglutinin gene of avian influenza virus H5 subtype in HVT vector vaccines, three HVT vector avian influenza virus H5 subtype (HVT-AI) viruses expressing the hemagglutinin gene were constructed using three promoters; the cytomegalovirus (CMV) promoter, the chicken β-actin (Bac) promoter, and CMV/Bac chimera (Pec) promoter. Of those three vector vaccines, HVT-AI with the CMV promoter induced significantly higher avian influenza virus (AIV) hemagglutinin inhibition titers than the other HVT-AI vaccines with the Bac or the Pec promoters, after inoculation into chickens at one day old. When evaluated with two of commercially available AIV enzyme-linked immunosorbent assay kits, the HVT-AI vaccines did not induce positive titers, indicating that these HVT-AI vaccines may be utilized for easy differentiation of vaccinated chickens from ones infected with field AIV