Evaluating how infectious bursal disease virus (IBDV) infection influences influenza H3N8 challenge in chickens

Infectious bursal disease virus (IBDV) causes an endemic immunosuppressive disease in chickens. Prior exposure to IBDV influences the pathogenesis and shedding of chicken strains of influenza A virus (IAV), but its effect on waterfowl strains is poorly understood. To address this, we inoculated 14-day-old specific pathogen-free chickens with low pathogenicity avian influenza strain A/Mallard/Alberta/156/01 (H3N8) and compared the replication, shedding, pathogenesis, transmission and intra-host evolution between immunocompetent chickens and chickens that had IBDV-mediated immune dysregulation due to a prior infection with strain F52/70 at 2 days of age. The IAV replicated in the upper respiratory tract, and the virus was shed from the oropharyngeal cavity, but there was no shedding from the cloaca and no transmission to sentinel chickens. IAV replication in chickens was associated with amino acid substitutions in the polymerase complex and HA. Prior IBDV infection had no significant effect on IAV pathogenicity, replication or shedding and had a modest effect on IAV diversity, increasing the number of amino acid substitutions from an average of 2.50 substitutions per sample (sd±1.83) in the Mock/IAV group to 4.75 (sd±1.81) in the IBDV/IAV group (P<0.01). Taken together, our data suggest that IBDV is unlikely to play a major role in the spillover or spread of waterfowl IAV strains in chicken flocks, although it could expand IAV diversity. This information is useful for informing preventative measures for controlling IAV in poultry flocks.