XK and influenza: Based on the antigenic differences in their surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), influenza A viruses are currently categorized into 18 different HA and 11 different NA subtypes (Tong et al., 2013), but only viruses with HA subtypes H1, H2, and H3 and NA subtypes N1 and N2 are known to cause influenza pandemics in humans (Kilbourne, 2006; Kalthoff et al., 2010; Li and Chen, 2014).