Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A(H5N1), also known as "bird flu", is a subtype of the influenza A virus which can cause lethal infections in humans, birds and animal species as well. Characterized by flu researchers as a highly pathogenic virus, it can evolve naturally or under laboratory conditions, emerging in new genetic structures with more deadly mutations. Recent flu studies led by Dutch virologists have developed a new version of the avian influenza virus making it much more contagious. Learn more about influenza A virus subtype H5N1 in this book.