Human influenza virus mainly affects the receptor subtype alpha 2.6 of the nasal cavity and throat, while H5N1 virus usually affects the lower respiratory tract receptor subtype alpha 2.3. This difference makes it difficult for avian influenza virus to spread through saliva droplets. However, the latest genetic sequencing consequences have shown that the Turkish bird flu virus is more likely to bind to receptor subtype alpha 2.6. The text is intended to explain:. ['Identification of different viruses.', 'Increased infectivity of avian influenza virus.', 'How does bird flu virus affect the human body.', 'Differences between human and avian influenza viruses.']