Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus that causes the disease avian influenza (often referred to as "bird flu"). It is enzootic (maintained in the population) in many bird populations, and also panzootic (affecting animals of many species over a wide area). A/H5N1 virus can also infect mammals (including humans) that have been exposed to infected birds; in these cases, symptoms can be severe or fatal. - Source: Wikipedia
