Avian (or bird) flu is caused by influenza viruses that occur naturally among birds. The highly pathogenic H5N1 variant is deadly to domestic fowl (such as chickens) and can be transmitted from birds to people. The H7N9 strain does not appear to sicken birds, but it has been recently infecting people. (see CDC website for more information)
Seasonal (or regular) flu is a respiratory illness that can be transmitted person to person. Most people have some immunity, and a vaccine is available.
Pandemic flu is a deadly human flu that causes a global outbreak, or pandemic, of serious illness. Because there is little natural immunity, the disease can spread easily from person to person. Currently, there is not pandemic flu in the world.
Influenza A is a family of viruses that affects birds and other animals. Avian influenza (also called "bird flu") refers to the strains of the virus that infect birds. Bird flu can cause widespread illness and death among birds, though there are many different strains, which vary in strength. All known subtypes of influenza circulate among wild birds, which are considered the natural host for influenza A viruses. Not all influenza A strains infect humans, however. Those that do can cause high death rates. There is much concern that a strain that infects people will change and easily transmit from person to person causing a global pandemic that kills millions.
Avian influenza (strain H5N1) was first detected in humans in 1997 in Hong Kong, where it infected both chickens and people. This was the first time the avian influenza virus had ever been found to jump directly from birds to humans. During this outbreak 18 people were hospitalized and 6 died. To control the outbreak 1.5 million chickens were killed. Since then there have been several other outbreaks in Asia and Europe.
How the Avian Flu is Spread
The disease is spread by the saliva, nasal secretions, and feces of infected animals, which other animals or humans then come in contact with. The only way to stop its spread is to kill the infected birds. There are several strains circulating among birds, but the H5N1 strain is also infecting people who have been in close contact with chickens.
Symptoms of avian influenza in humans have ranged from typical influenza-like symptoms, such as fever, cough, sore throat, and muscle aches, to eye infections, pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications. The symptoms may depend upon the infection.
The US Department of Agriculture (USDA) requires the quarantine of any birds, fowl (e.g., chickens and ducks), exotic birds, and pets, before they enter the US It is safe to eat chicken as long as it is thoroughly cooked because cooking kills the virus. Travelers to countries in Asia with documented H5N1 outbreaks are advised to avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with feces from poultry or other animals.