Chicken anaemia virus enhances and prolongs subsequent avian influenza (H9N2) and infectious bronchitis viral infections.

Immunosuppressive viral diseases have a great economic importance in the poultry industry due to the increased susceptibility to secondary infections. Chicken anaemia virus (CAV) is one of the major immunosuppressive diseases in chickens. In addition, low pathogenic avian influenza (LPAI) of subtype H9N2 and infectious bronchitis (IB) viruses are among the most frequently reported respiratory viral diseases in poultry worldwide. In the present study, specific pathogen free chickens were used to understand the impact of CAV on secondary infection with LPAI-H9N2 or IB viruses. Clinical outcomes, viral shedding dynamics, and cytokine levels wereassessed. The results exhibit that chickens previously infected with CAV produceconsiderablyhigher titresof LPAI-H9N2 or IB viruses in the oropharyngeal swabs (P < 0.05), tracheas and kidneys. In addition, the immunologic effect of CAV provokedthe development of clinical signs of LPAI-H9N2 and IB virus infections. Moreover, results suggested that pre-infection with CAV directly correlated with elevated levels of IL-6 and IFNγ. These findings underline the importance of CAV pre-infection on LPAI-H9N2 or IB infection in chickens, and indicate that co-circulation of CAV can contribute to the spread and evolution of LPAI H9N2 and IB viruses.