Scientists fear that the bird flu virus could change into a form that can easily spread between people, which would result in an extremely contagious and lethal disease.

This could happen if someone who is already infected with the human flu virus catches bird flu.

The two viruses could recombine inside the victim’s body, and produce a hybrid that could readily spread from person to person.

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.

Bird flu in the news >