Pathogenicity and cytokine response in birds experimentally infected with H9N2 avian influenza virus in a single or mixed infection with IBV

Abstract

Avian influenza H9N2 and Infectious bronchitis virus (IBV) are considered of major significance and have a great economic impact because they are able to induce disease state independently or in association with each other, they have been frequently reported from different broiler chicken flocks in Egypt. Co-infection of AIV-H9N2 and IBV was one of the most common causes of respiratory problems and mortalities in the Egyptian poultry flocks during last few years. The lack of vaccination against AIV-H9N2 with its potential immunosuppressive effect may be the main reason for the high prevalence of respiratory infections. The present study was designed to investigate the pathogenicity and immunogenicity of AIV-H9N2 and IBV in SPF chicks in single and mixed infections. In this study, eighty 1-day-old specific pathogen free chicks were divided into four distinct groups. Group 1 remained uninfected as negative control group; groups 2, 3 and 4 were inoculated with either AIV-H9N2 at 14 days old or IBV at 17 days old or co infected with AIV-H9N2 followed by IBV three days postinoculation respectively. Chicks were monitored for clinical and pathological changes, virus shedding and both Interleukin-6 (IL6) and Interferon gamma (IFNγ) cytokines immune responses. Experimentally infected chicks of group 2 showed no clinical signs, however mild respiratory signs were shown in group 3.Death of one bird was observed in groups 3 and 4 in addition to severe clinical signs. Post mortem examination of infected chicks of group 2 showed mild congestion in lung. In group 3, lesions were found in lungs and kidneys while in group 4, lesions were more severe and extended for longer period than group 3.