Avian influenza H7N9/13 and H7N7/13: A comparative virulence study in chickens, pigeons, and ferrets

Human cases caused by a novel avian H7N9-virus in China emphasize the zoonotic potential of that subtype. We compared infectivity and pathogenicity of the novel H7N9-virus and a recent European avian H7N7-strain in chickens, pigeons and ferrets. Neither virus did induce signs of disease despite of substantial replication in inoculated chickens and rapid transmission to contact chickens. Evidence for replication of both viruses in pigeons, albeit at lower levels of RNA excretion, was also detected. No clear-cut differences between the two H7-isolates emerged regarding replication and antibody development in avian hosts. In ferrets, in contrast, enhanced replication of the avian H7N9-virus compared to the H7N7-strain was observed with significant differences of viral presence, e.g., in nasal washes, lung and cerebellum samples. Importantly, both viruses showed potential to spread into the brain of mammals. We conclude, that efficient asymptomatic viral replication and shedding as shown for the chickens facilitates spread of H7-viruses, which may harbor a zoonotic potential. Biosafety measures are required in handling poultry infected with avian influenza viruses of the H7 subtype independent of their pathogenicity for gallinaceous poultry.