Bird flu

“Flu”, or influenza, is caused by the influenza virus. Outbreaks occur in humans every winter. It is spread by breathing in droplets of water in the air containing the virus that have been coughed or sneezed out by another person. The usual symptoms in adults are fever, muscle aches and cough, and are usually bad enough to make you stay in bed for 2 or 3 days.

There are many flu viruses, which can be type A, B or C. Within these three types, there are many different subtypes depending on what is on the surface of the virus. The things found on the surface are proteins, and these can be a protein called haemagglutinin (H) or a type called neuraminidase (N). Different types of H and N are given different numbers, and these numbers are what give the types of flu their names (e.g. H5N1).

Many animals can get the flu. The illness caused in birds, “bird flu”, is also called “avian influenza”. While all birds can be infected with bird flu, many wild birds can have a virus without any signs of being ill. Other birds, including chickens, ducks and geese, become sick when infected with the same bird flu viruses. In poultry, bird flu viruses can cause two different types of disease. One is fairly common and is a mild illness, and the other is rare and deadly.

Flu viruses normally only infect one species and do not cause infection in other species. However, human cases of bird flu have now been seen.

From what has been seen so far, it is difficult for humans to catch the H5N1 virus.

As far as we know, the way that humans get infected with the H5N1 bird flu virus is only by very close contact with dead or sick birds (for example butchering and preparation of infected birds for eating, or playing in an area with waste from free-ranging poultry).

Most cases of human bird flu have occurred in rural households where small flocks of poultry are kept and very few cases have been detected in the groups thought to be at high risk (for example commercial poultry workers and vets). No direct human to human spread has been confirmed.

In many patients, the disease caused by the H5N1 virus makes the patient ill very rapidly. Initial symptoms include:

• high fever (usually higher than 38°C)
• severe aches and pains all over the body

And possibly:

• breathlessness
• diarrhoea
• vomiting
• abdominal pain
• chest pain

There may be more symptoms than those listed and not all patients have the symptoms above.

Unfortunately, the current flu vaccine that many people take each year does not protect against bird flu and there is no vaccine currently available for bird flu. Anti-viral drugs can be used for bird flu, for example oseltamivir (known as Tamiflu®). Anti-virals may be given to help prevent infection with bird flu if taken before a person is infected or to help improve survival from bird flu if given within 48 hours of the first symptoms. In the absence of a vaccine, anti-virals are the only medical intervention for prevention and treatment.

Scientists fear that the H5N1 and simialr bird flu viruses could change into a form that can easily infect and spread between people, which would result in an extremely contagious and lethal disease. If this were to happen, the resulting virus would probably be something humans have never been exposed to before. With no immune defences, the infection could cause terrible illness, such as occurred in the 1918–1919 Spanish flu pandemic, which killed an estimated 40–50 million people worldwide.

This material was compiled with the help of ERS expert, Mark Woodhead.