South-East Asia Regional Conference on Epidemiology

<strong>South</strong>-<strong>East</strong> <strong>Asia</strong> <strong>Regional</strong> <strong>Conference</strong> on Epidemiology | 85
Fig. 2: Amino acid substitutions in HA occurred much less in H1N1pdm virus than seasonal H1N1 viruses.
Therefore, H1N1pdm virus is antigenically similar to Spanish flu virus
Table 1: Virological findings of H1N1pdm
pathogenic properties. The possibility of emergence of a highly pathogenic human virus is a big issue
for the pandemic. For adaptation to humans two factors have been identified (Table 2).
The haemagglutinin (HA) protein of influenza virus binds to target cells. For, the avian virus
specific receptors comprise sialic acid α2,3 galactose (SA α (2-3)Gal), which distribute in bird tissues,
whereas human virus binds preferentially to sialic acid α2,6 galactose (SA α(2-6)Gal) sugar chains
present in mammalian bodies. Avian viruses will infect preferentially bird species and will not infect
humans efficiently. However, this barrier is not absolute, and indeed H5N1 infects humans even less
efficiently. One amino acid substitution, due to a gene mutation at the receptor binding site of HA to
the human virus type, changes the receptor preference and determines the change of the host range.
For H5N1 avian virus to become a human type, such a mutation is likely required.