Other names: Bird flu, or avian flu
Bird flu, or avian flu, is an infectious type of influenza that spreads among birds. In rare cases, it can affect humans.
More than a dozen types of bird flu have been identified, including the two strains that have most recently infected humans — H5N1 and H7N9. When bird flu does strike humans, it can be deadly.
A new strain of bird flu was identified in China in 2013. The influenza A virus is termed H7N9 (H7N9 Chinese bird flu). The identification of the virus (H7N9) was reported Mar. 31, 2013; the strain is antigenically different from the H5N1 bird flu virus. Unfortunately, the H7N9 strain of bird flu seems to be genetically unstable. Since its discovery, at least 48 different subtypes of H7N9 have been identified. Because some H7N9 viruses are persistent in some chicken flocks in China, researchers are concerned that the strains will continue to swap genes with other flu viruses and may start a new pandemic.
Signs and symptoms of bird flu may begin within two to eight days of infection, depending on the type. In most cases, they resemble those of conventional influenza, including:
- Sore throat
- Muscle aches
- Shortness of breath
- Diarrhoea, vomiting, abdominal (tummy) pain, chest pain, and bleeding from the nose and gums have also been reported as early symptoms in some people.
These symptoms can come on suddenly. The time from infection to the start of symptoms (incubation period) is usually three to five days, although in some cases it can be up to seven days.
Bird flu is caused by strains of the influenza virus that have evolved to be specially adapted to enter avian cells. There are three main types of influenza: A, B, and C.
Bird flu occurs naturally in wild waterfowl and can spread into domestic poultry, such as chickens, turkeys, ducks and geese. The disease is transmitted via contact with an infected bird's feces, or secretions from its nose, mouth or eyes.
Open-air markets, where eggs and birds are sold in crowded and unsanitary conditions, are hotbeds of infection and can spread the disease into the wider community.