The flu is caused by the influenza virus (the family Orthomyxoviridae), which targets the respiratory tract by binding to the surface of cells. Then the virus releases ribonucleic acid , its genetic information (RNA) into the cell's nucleus to replicate ...

Phase 1 - no viruses circulating among animals have been reported to cause infections in humans. Phase 2 - an animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered ...