Different Replication Profiles in Specific-Pathogen-Free Chickens of Two H7 Low Pathogenic Avian Influenza Viruses Isolated from Wild Birds

During an active wild bird survey conducted in Belgium from 2007 to 2011, two low pathogenic avian influenza (LPAI) H7 viruses were isolated from wild birds: an H7N1 virus from a common shelduck (Tadorna tadorna) and an H7N7 virus from a Canada goose (Branta canadensis). The H7 sequence analyses and intravenous pathogenicity indices indicated that they were both low pathogenic isolates and genetically related to other recent European H7 LPAIs isolated from wild birds. Interestingly, the two isolates showed different replication profiles in specific-pathogen-free (SPF) chickens, but poultry can be at risk from both. Indeed, the H7N1 isolated from the common shelduck had the ability to infect and to replicate efficiently in SPF chickens as indicated by high oropharyngeal and cloacal excretions compatible with efficient transmission as well as strong immune responses. On the other hand, the H7N7 isolated from the Canada goose presented a lower replication profile because the inoculated chickens excreted less virus, mostly via the oropharyngeal route, and only three chickens seroconverted. None of the chickens showed clinical signs during the entire infection. Our study using an SPF chicken model underlines that the mechanisms of adaptation of LPAIs in poultry remain unpredictable and are still poorly understood but it represents a powerful tool to gain a better evaluation of the risks of LPAI circulation in poultry.