SINGAPORE, May 4 (Reuters) While the world focuses on battling the spread of the deadly bird flu, nearly 150 different strains of the virus with the potential to cause a global pandemic were laying in wait, scientists warned.
''It is dangerous just to focus on H5N1,'' Hiroshi Kida, of Japan's Hokkaido University yesterday, said on the sidelines of a bird flu conference in Singapore organised by the Lancet medical journal.
Kida said H5N1 virus -- responsible for 113 deaths around the world -- was one of at least 144 potential different strains which posed a threat to humans.
The different strains were possible because of combinations of proteins within the virus.
All the strains were present in ducks, which act as carriers often without showing any flu symptoms, he said.
''None of the ... subtypes can be ruled out as potential candidates for future pandemics,'' Kida told the conference.
Bird flu viruses are a threat to humans because we have no natural immunity to most of them and because they can jump directly from birds to people -- just as one strain did in 1918, triggering a pandemic in which an estimated 50 million died.
In 2003, an outbreak of highly pathogenic H7N7 bird flu infected 89 people in Holland and killed one. Bird flu strains H9N2, H7N2 and H7N3 have also infected people.
But it is fast-spreading H5N1 that has scientists most worried at the moment. It is known to have killed at least 113 of the 205 people it has infected and killed or led to the culling of about 200 million chickens.
Virologist Malik Peiris told the conference the assumption that H5N1 will wear itself out if it triggers a pandemic might be wrong.
''If this virus becomes a pandemic, will it attenuate its virulence in humans? I think that would be a rather optimistic assumption to make,'' said Peiris of the University of Hong Kong.
During past pandemics, flu viruses quickly evolved to effectively wear themselves out and kill only a small percentage of people.
Reuters KD GC1015