three subtypes of hemagglutinin (H1, H2, and H3) and two subtypes of neuraminidase (N1 and N2) have caused sustained epidemics in the human population. Birds are hosts for all influenza A subtypes ...

hemagglutinin and neuraminidase. There are 16 different hemagglutinins and nine different neuraminidases, and reassortment of these two antigens determines the influenza A virus subtype (e.g ...