Bird flu, or avian influenza, is a viral disease that causes illness in many species of birds. It has been around for more than 100 years. There are 15 types of bird flu.

Is it the same as H5N1?

H5N1 is the strain of bird flu that is currently causing worldwide concern. It has proved lethal to poultry and has infected some people.

Why should we be worried about this strain?

H5N1 bird flu has shown an ability to jump from birds into several other species. Human cases reported so far were infected with the disease after coming into contact with chickens and ducks. We have no immunity to animal viruses.

How is bird flu spread?

Many millions of migratory birds and wildfowl carry the disease, and some species of duck are able to carry the virus without showing symptoms. Illegal bird smuggling and the movement of domestic birds has also helped to spread the disease between countries. Birds pass on the virus through their droppings, feathers, saliva and breath. If an infected duck or other water bird uses the same pond or stretch of water as other birds, the infection can be passed on through faeces or feathers shed in the water.

How do people catch bird flu?

Most of the human cases caught the virus when they were preparing chickens for slaughter, but some contracted it by handling infected birds.

When will bird flu become a human disease capable of spreading from one person to another?

Most experts think that this will happen at some point in the next two years. It is in the nature of the flu virus to mutate regularly. This is how some previous flu pandemics have begun. All that is needed is for someone with human flu to catch H5N1 bird flu from an infected bird and the virus could mutate in such a way that it combines the human flu’s ability to spread with H5N1’s severe symptoms. Alternatively, the bird flu virus could gradually adapt and jump the species barrier by itself.

Are there other examples of diseases that have jumped from animals to humans?

Past flu viruses have made the leap from animal to human, in particular the Spanish flu that killed tens of millions in 1918-19. It is now accepted that HIV originally spread from animals to humans. Studies suggest that Sars may have spread from bats, and UK outbreaks of Creutzfeldt-Jakob disease in the 1990s were linked to the incidence of bovine spongiform encephalopathy in cattle.

Is it just birds, or do other animals carry this disease?

Several species other than birds have been found to carry the bird flu virus. Pigs in Indonesia have caught H5N1, which is worrying as they can also carry the human flu virus and could act as “mixing vessels” for the two viruses, allowing them to form a new version of flu that could spread easily between people. Tigers and cats have also been infected, and cats are known to be able to infect other cats.

What makes the bird flu virus mutate?

All flu viruses, even “normal” human flu, mutate regularly — the virus mutates each time it replicates. Flu viruses are unstable and make imperfect copies of themselves, allowing different genetic variations to crop up quickly.

When the H5N1 virus mutates, will it be deadly?

We don’t yet know. Often when a flu virus mutates, there is a trade-off: it may change to become more transmissible within a species but at the same time become less virulent. We have no immunity to any H5 strain of flu.

Explore World News

• World Agenda

• Iraq News

• US & Americas News

• Europe News

• Middle East News

• Afghanistan News

• Asia News

• Africa News

• Ireland News

Times Recommends

• It’s only Brits who don’t appreciate me, says Blair
• Party’s over for Greek graspers
• White House tightens security for Xmas marathon