Scientists trace origins of deadly avian flu

It will be difficult to eradicate avian influenza, according to scientists who tracked the genetic origins of the virus.

The H5N1 virus causes a highly pathogenic type of bird flu that killed 24 people in 2003-04 in Asian countries.

INDEPTH: Avian flu

"Our results suggest that H5N1 viruses with pandemic potential have become endemic in the region and are not easily eradicable," Dr. Yi Y Guan, of the University of Hong Kong, and his colleagues wrote in Thursday's issue of the journal Nature.

"These developments pose a threat to public and veterinary health in the region and potentially the world, and suggest that long-term controls are required," they added.

The scientists say "Z genotype" of the H5N1 strain was responsible for this year's deaths. The team studied how it evolved from an ancestor thought to be responsible for an outbreak that killed people in Hong Kong in 1997.

The H5N1 virus is not able to spread between humans. Scientists fear if the virus gains the ability, it could mutate more quickly into a form that people have no immunity against, triggering a pandemic.

The researchers warn the risks can only be reduced, but not eliminated, by culling birds.

They say domestic ducks in southern China likely played a key role in generating the virus, and wild birds may have contributed to its spread in Asia.