Pathogenicity of Bordetella avium under immunosuppression induced by Reticuloendotheliosis virus in specific-pathogen-free chickens.

Multiple infections of Bordetella avium (B. avium) with virus, especially immunosuppressive virus, have become more and more severe in chickens in China. The increasing morbidity and mortality of its complications have amplified concerns about the impact of B. avium on animal health. To evaluate the pathogenicity of B. avium under immunosuppression status, we developed four types of Reticuloendotheliosis virus (REV) infection models. After a comparison of body weight, relative immune organ index, Newcastle disease virus antibody titers and lymphocyte ratio, we chose the early age with low dose infection as our immunosuppressive model. To investigate the pathogenicity of B. avium under this model, a study was completed in which chickens were inoculated with REV-only, B. avium-only, both agents (REV -B. avium) or first inoculated with REV and 5 d later with B. avium (REV/B. avium). Results revealed that antibody titers to B. avium, concentrations of IFN-γ and SIgA were decreased in coinfected chickens when compared to the B. avium-only chickens, but the changing trend was similar between REV/B. avium and B. avium-only groups. Overall, REV did enhance the pathogenicity of B. avium. However, B. avium-only did not cause severe immune dysfunction unless chicks were coinfected with REV. REV preceding infection with B. avium showed mild impairment, which needs further exploration.