Understanding Avian Influenza Avian (or bird) flu: a disease caused by avian influenza viruses that occurs naturally among birds. They cause disease in infected birds that ranges from mild or asymptomatic to severe illness and death. In rare cases, it can be transmitted from birds to humans.
Pandemic Flu A pandemic flu is a new influenza virus that could be a much more serious flu virus than seen in a typical flu season. Different from the typical strains of flu, humans would have no or little natural resistance to a new strain of influenza.
Seasonal Flu Influenza is a contagious respiratory disease caused by a virus which infects many parts of the body, including the lungs. Someone who has the flu spreads the virus by sneezing, coughing, or even talking. Flu may be transmitted by direct hand contact.