Only a handful of people are believed to have caught bird flu from another person, and only in instances of extreme close contact. What scientists worry about is the virus mutating into a strain that passes easily from person to person.

The Impact

The most immediate threat is to the poultry industry in affected areas because governments are likely to slaughter stocks to prevent further spread of the virus.

Authorities also want to stamp out any outbreak swiftly to prevent opportunities for the virus to mutate into a form that could become dangerous to humans and spark a human influenza pandemic. The farther the virus spreads the more of it there is in the environment and the more opportunities it has to mutate.

Danger of H5N1 to Humans

Although 117 people have been infected with the strain since the outbreak began in Asia two years ago and 60 of them have died, H5N1 does not easily infect humans, experts say. People who have become infected are mostly those who have been in very close contact with birds, such as poultry farmers.

A handful of people are believed to have caught the virus from another person, but again, only in instances of extreme close contact. What scientists worry about is the virus mutating into a strain that passes easily from person to person.

How Does H5N1 Compare to Other Bird Flu Strains?

H5N1 is one of more than 100 possible strains of bird flu. Some are more deadly than others.

There can be a highly deadly strain of H5N1, or a less lethal strain. British turkeys were found with an H5N1 strain in 1992, but that was not related to the particularly deadly Asian H5N1 strain.

H5N1 and Food Safety

Experts say that eating cooked chicken is not risky. The virus is killed in seconds at temperatures of 70 degrees celsius. It is not thought to survive in frozen raw chicken either, said Peter Roeder, an animal health expert at the UN's Food and Agriculture Organization.

Hygiene precautions surrounding the handling of raw poultry should be taken, as they normally are to prevent infection from bugs such as salmonella. However, many countries have banned imports of raw poultry from affected areas.

Regular Flu Vaccinations

Regular seasonal flu vaccination is not thought to protect people against H5N1.

One of the main reasons authorities recommend the vaccination in areas affected by bird flu is to prevent the two viruses mixing inside a person and spawning a dangerous hybrid that could spark a human pandemic.