HONG KONG, Feb 22 (Reuters) Virus samples taken from wild birds found dead in Hong Kong recently were closely linked to a strain of the H5N1 virus that surfaced in Japan and South Korea in 2004, but not the one spreading in Europe, a top scientist said.
This finding suggests that apart from the strain circulating in Europe, there could be a reservoir of another strain of the deadly H5N1 virus that is entrenched, probably in wild birds, said microbiologist Malik Peiris of the University of Hong Kong.
Experts believe that the more distinct and lethal strains there are, the greater would be the risk to humans.
Eight wild birds and two stray chickens were found dead with the H5N1 avian influenza virus over the past month in Hong Kong although poultry farms here have not been affected so far.
Hong Kong scientists analysing virus isolates, or samples, from the dead birds found that their genotype, or DNA makeup, belong to a strain called the V-genotype, which was found in dead birds in Japan and South Korea in 2004, Peiris said in an interview yesterday.
''The viruses are in the process of being genetically analysed, they are similar ... It is the V-genotype, it was found in (bird) outbreaks in Japan and Korea in 2004. They are not identical, but the same genotype,'' he said.
''The Japan outbreak is thought to have been introduced by wild birds as well. So one of the things under investigation is whether this is a genotype that is established in wild birds ... one can't jump to conclusions, but this is one possibility.'' After inundating many parts of Asia since 2003, the virus has spread rapidly across Europe, into Africa and now India where people live side-by-side with livestock and domestic fowl.
While most of the more than 90 people it has killed since 2003 contracted the virus directly from birds, experts fear the virus will mutate and become easily spread among people, triggering a pandemic that will kill millions of people.
Peiris said the strain spreading in Europe was not linked to the V-genotype, but rather to the strain found in dead migratory birds in China's Qinghai Lake in the middle of 2005.
The World Health Organisation, on its Web site, says viruses from Qinghai Lake showed a distinctive mutation that led to greater death rates in birds and mice during experiments. More than 6,000 birds died at Qinghai and the WHO says the mutated strain involved there ''signalled an important change in the way the virus interacts with its natural reservoir host''.
Peiris said the strain in Hong Kong was not similar to the virus found in Nigeria or Europe.
''Those found in Turkey, Romania and Siberia are all closely related to the one in Qinghai. But the Hong Kong viruses are not closely related to the Qinghai one,'' he said.
The V-genotype is not known to have surfaced in countries in Southeast Asia, Peiris added.
The WHO said research conducted in Southeast Asia has recently shown that multiple distinct lineages of the H5N1 virus have become established in poultry in different geographical regions, indicating the virus in its different forms has become endemic in parts of Asia.
That research also detected highly pathogenic H5N1 virus in apparently healthy migratory birds, further raising the risk of the virus spreading and infecting more people.
Commenting on the danger that wild birds pose, Peiris said: ''There is very little risk of infection directly from wild birds to humans. The risk is that wild birds can introduce the virus into poultry, then the virus amplifies in the poultry and of course, the human exposure then becomes much greater.'' It was in Hong Kong that the H5N1 made its first known jump to humans in 1997, killing six people. Since then, the government has implemented strict measures to keep the virus out.
REUTERS SB VC1702