Why doesn bird flu spread easily from human to human?
Both bird and human flu viruses infect people by attaching themselves to cells in the respiratory tract. Currently, bird and human strains do this in two different locations. Bird viruses prefer to bind with molecules located deep within the lungs. This remote location inside the body makes it more difficult to spread the bird flu virus by coughing or sneezing. But scientists warn that the H5N1 virus could adapt and affect cells much higher up in the airway, where human flu viruses typically bind. If that occurs, the chances of a pandemic could be greatly increased.
