Co-circulation of three HA and two NA subtypes of avian influenza viruses in Huzhou, China, April 2013: implication for the origin of the novel H7N9 virus

We detected three avian influenza HA subtypes (H7, H9 and H5) and two NA subtypes (N9 and N2), as well as H7N9-related reassortant intermediates H9N9, co-circulating among poultry in Huzhou, China, during April 2013. The co-circulation not only reveals that Huzhou is one of the geographic origins of the novel H7N9 virus, but also poses a potential threat to humans in the future.