Pathological changes, shedding pattern and cytokines responses in chicks infected with avian influenza-H9N2 and/or infectious bronchitis viruses.

Avian influenza H9N2 (AIV-H9N2) and Infectious bronchitis (IB) viruses are the most commonly isolated viruses from poultry flocks suffering from respiratory signs with mortalities. The outcome of co-infection with both viruses hasn't been yet well understood. 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 or IBV or co infected with AIV-H9N2 followed by IBV three days post inoculation respectively. Chicks were monitored for clinical and pathological changes, virus shedding and both Interleukin-6 (IL6) and Interferon gamma (IFNγ) cytokines immune responses. Clinical signs varied from mild to moderate respiratory signs in all challenged groups but were more severe in group 4 with mortalities in groups 3 and 4. Tracheal shedding of both viruses washigher in group 4 than group 2 and 3. Mean AIV-H9 virus titer in lung and kidney was higher in group 4 than group 2 in all time points. IFNγ mRNA gene expression in lung was significantly lower in groups3 and 4. In conclusion, this study reports that co-infection of chicks with both viruses enhances the pathogenicity, increases both viruses shedding and extend AIV-H9 replication with impairment of IFNγ stimulation in lung.