Figure 5.

The reverse zoonosis of influenza predicted by glycosylation patterns of H1N1 HA and NA. The glycosylation patterns of HA and NA for human and swine species isolated between 1918 and 2015 were analyzed. A gradual increase in glycosylations in cluster II was observed in swine HA in recent years, except for the year 1939 when glycosylation occurred in all three clusters (A). The position 71 glycosylation in HA and the position 434 glycosylation in NA were simultaneously identified from 1986 to 2009 in human isolates (B). The cosegregation of the two independent mutations could be considered as a genetic characteristic of adaptation to humans. The swine isolates had a glycosylation at position 71 in HA and position 434 in NA in 2005, indicating “reverse zoonosis” from humans into swine.