Comparison of the regions of the organism infected by the virus of human influenza and the virus of avian influenza. The virus of human influenza is mainly présent into the upper respiratory system : nasal mucosa, sinus, pharynx, trachea and main bronchi (in green). So, it can easily transmit itself to the family circle, via the droplets of cough. The virus of avian influenza (H5N1) preferentially colonize the depth of the lung : bronchioli and pulmonary alveoli (in blue). So, it is little contagious, as it does not rise enough into the respiratory system to be expelled with the cough.
