Bird flu (avian influenza) is an infection with strains of influenza that normally occur in wild birds, domestic poultry, and sometimes pigs.
Bird flu is caused by several strains of influenza A virus that normally infect wild birds. The infection can be easily spread to domestic birds and sometimes pigs. However, it rarely spreads from animals to people. It spreads to people mainly when the genetic material of the virus changes (mutates), enabling the virus to attach to cells in the human respiratory tract. Nearly all people who have been infected with bird flu have had close contact with an infected bird, usually one that is sick or dead. Bird flu almost never spreads from person to person. However, experts are concerned that additional mutations could enable the virus to spread more easily from person to person. Then, bird flu could spread rapidly and widely, causing a major worldwide epidemic (a pandemic).
Human infection with the avian flu strain H5N1 (see Influenza types and strains) first occurred in Hong Kong in 1997 and then spread to Vietnam, then to Indonesia, Cambodia, China, Thailand, Turkey, Azerbaijan, Djibouti, Egypt, and Iraq. Since 2003, there have been more than 600 cases of human H5N1 infection, with 391 deaths, in 15 countries in Asia, Africa, the Pacific, Europe, and the Near East.
In 2013, an outbreak began in southeastern China. It involved the avian flu strain H7N9. As of mid 2014, there have been 423 cases of human H7N9 infection in China and 4 cases in Taiwan. The infection has occurred mainly in communities that consume poultry from live poultry markets.
Other strains of the avian flu virus have also caused sporadic outbreaks of infection in people. However, in these outbreaks, the virus has not spread from person to person. In April 2014, one person in the Sichuan province of China died after getting H5N6 bird flu, but the virus has not spread to other people.
Symptoms in people vary depending on which strain of the virus is the cause. H5N1 and H7N9, which cause most cases in bird flu in people, have similar effects.
People may have extreme difficulty breathing and flu-like symptoms (such as fever, cough, sore throat, and muscle aches). Some people have conjunctivitis or pneumonia.
The risk of death has been high: 30% in one outbreak and more than 60% in another.
If people have flu-like symptoms and have had contact with birds in an area where birds are known to carry the infection or contact with a person infected with bird flu, they should contact a doctor.
The doctor can send a sample taken by swabbing the nose or throat to be tested.
Infected people are given oseltamivir or zanamivir (antiviral drugs that are used to treat influenza—see Influenza (Flu) : Treatment), which are usually effective.