Avian flu is caused by influenza viruses that occur naturally among wild birds. “Low pathogenic avian flu” is common in birds and causes few problems. “Highly pathogenic avian flu” is deadly to domestic fowl, can be transmitted from birds to humans, and is deadly to humans. There is virtually no human immunity, and human vaccine availability is very limited.
Bird flu is commonly used to refer to avian flu. Bird flu viruses infect birds, including chickens, other poultry, and wild birds such as ducks.
Pandemic flu is virulent human influenza virus that causes a global outbreak of serious illness. The illness typically extends over a wide geographic area, spreads rapidly, and affects a large portion of the population at the same time. Because there is little natural immunity, the disease can be spread easily from person to person.
H1N1 flu (also called swine flu) is a new type of flu first detected in the United States in April 2009. It was originally referred to as swine flu because the virus that causes it is similar to one found in pigs. However, the H1N1 virus is also similar to other flu viruses found in birds and humans, and it cannot be contracted through eating or handling pork products. The virus spreads from person to person, probably in much the same way that regular seasonal influenza viruses spread.
Seasonal flu (also called common flu) is a respiratory illness that can be transmitted from person to person. Most people have some immunity, and a vaccine is available.