Bird flu, or avian flu, is an infectious viral illness that spreads among birds. In rare cases it can affect humans.

There are many types of bird flu, most of which are harmless to humans. However, two types have caused serious concern in recent years. These are the H5N1 (since 1997) and H7N9 (since 2013) viruses.

Although these viruses don't infect people easily and are usually not transmitted from human to human, several people have been infected around the world, leading to a number of deaths.

Other bird flu viruses (particularly H7N7 and H9N2) have also infected people, but these have rarely caused severe illness. 

Bird flu affects many species of birds, including chickens, ducks, turkeys and geese. It can be passed between commercial, wild and pet birds. Birds do not always get sick from infection, so seemingly healthy birds may still pose a risk to people who come into contact with them.

Signs and symptoms

Like other types of flu, bird flu symptoms often include a high temperature, aching muscles, headache and respiratory symptoms such as a cough or runny nose. Most people with the condition rapidly develop more severe respiratory problems.

Diarrhoea, vomiting, abdominal (tummy) pain, chest pain, and bleeding from the nose and gums have also been reported as early symptoms in some people.

Within days, potentially fatal complications such as acute respiratory distress syndrome and multiple organ failure may develop.

Having flu-like symptoms is extremely unlikely to mean you have bird flu, unless you have been in recent close contact with birds in an area where outbreaks have been reported.

Read more about the symptoms of bird flu and diagnosing bird flu.

Human cases

The World Health Organization (WHO) has confirmed that by July 2013, 633 people had been infected with the H5N1 virus and 377 had died. These cases occurred in Azerbaijan, Bangladesh, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Laos, Myanmar, Nigeria, Pakistan, Thailand, Turkey and Vietnam. Indonesia, Egypt and Vietnam experienced most cases and fatalities.

Since March 2013, there have been reports of people being infected with the H7N9 virus in eastern China. By July 2013, there were 134 confirmed cases and 43 deaths.

Most cases were among middle-aged to elderly men. With the exception of one person, who travelled to Taiwan while infected, there have been no reports of human infections outside mainland China.

For both viruses, there have been some reports of limited human to human transmission, usually as a result of very close contact between family members.

People who have had bird flu generally developed the virus after coming into close and prolonged contact with infected birds. Millions of birds have been killed during outbreaks to prevent the disease spreading and being passed on to people.

How bird flu spreads to humans

Bird flu is spread through direct contact with infected birds (dead or alive), an infected bird's droppings, or secretions from their eyes or respiratory tract.

Close and prolonged contact with an infected bird is generally required for the infection to spread to humans. For example:

• touching infected birds that are dead or alive
• inhaling or being in contact with dried dust from the droppings or bedding of infected birds
• inhaling or being in contact with droplets sneezed by infected birds
• culling, slaughtering, butchering or preparing infected poultry for cooking

Bird flu is not transmitted through cooked food. Poultry and eggs are safe to eat in areas that have experienced outbreaks of bird flu.

There have been few reports of bird flu passing from person to person.

Read more about how bird flu spreads to humans.

Preventing bird flu

Although it is difficult to prevent the spread of bird flu between birds, there are a number of things you can do to reduce your risk when you visit areas where outbreaks have been reported, such as:

• avoid visiting live animal markets and poultry farms
• avoid contact with surfaces that are contaminated with bird droppings
• don't pick up or touch birds (dead or alive)
• don't eat or handle undercooked or raw poultry, egg or duck dishes
• don't bring any live poultry products back to the UK, including feathers
• always practice good personal hygiene, such as washing your hands regularly

There are no restrictions on travel to countries that have been or are currently affected by bird flu.

Read more about preventing bird flu and treating bird flu in humans.