The neuraminidase of bat influenza viruses is not a neuraminidase

Influenza A viruses are classified into subtypes according to their two viral glycoproteins, hemagglutinin (HA) and neuraminidase (NA). These viruses are known to infect multiple animal species, including humans, pigs, horses, dogs, sea mammals, chickens, ducks, and other birds. Although humans are sporadically infected with avian influenza virus strains belonging to multiple subtypes, only H1, H2, and H3 HA subtypes and N1 and N2 NA subtypes have been documented to cause pandemics and annual epidemics of influenza in humans. By contrast, all H16 and N9 subtypes of influenza A viruses are found circulating in birds. The recent discovery of influenza A viruses clearly distinct from any known avian influenza A virus subtype in little yellow-shouldered bats from Guatemala has been the first example of an influenza A virus subtype not found in avian species (1). Bat influenza viruses have glycoproteins related to the HA and NA of influenza A virus, which prompted to the classification of these viruses as H17N10 influenza A virus. The crystal structure of the N10 glycoprotein is now solved independently by Li et al. (2) and Zhu et al. (3) in PNAS, and these works provide important clues on the characteristics of these newly discovered influenza viruses.