Answer:
Lacks the right key to unlock many cells.
Explanation:
Avian influenza (H5 N1) rarely transmitted from poultry to humans because it lacks the right key to unlock many cells in the upper respiratory tract so due to this action the virus is rarely transmitted to humans. Sometimes it is lethal to humans due to absence of antibodies for this type of virus. It is rarely spread from person to person due to inability to enters the other human body.
