[BEIJING] A previously unidentified strain of the H5N1 avian flu virus found in poultry in southern China has spread from birds to people in a third wave of infection, rekindling fears that China's poultry vaccination programme is ineffective.
The results were published online in the Proceedings of the National Academy of Sciences yesterday (30 October).
"This strain may have begun the third wave of transmission of H5N1 avian flu and could potentially spread throughout Eurasia," say the researchers.
Genetic analysis indicates that the new strain, called Fujian-like because it was first identified in Fujian province in May 2005, became the dominant strain in southern China early this year.
It is responsible for recent human H5N1 infections in China and has already spread among poultry in Hong Kong, Laos, Malaysia and Thailand.
The strain may have become resistant to vaccines, and may even be aided by China's compulsory chicken vaccination programme that was introduced in September 2005.
The researchers tested chickens, ducks and geese randomly caught in markets in six southern Chinese provinces for the H5N1 virus between July 2005 and June 2006.
They found that 2.4 per cent tested positive for H5N1, an increase of 1.5 per cent from the preceding 12 months, pointing to an increase in virus activity among poultry that the researchers suggest is caused by the Fujian-like virus.
The virus became increasingly dominant over other H5N1 strains, increasing from three per cent of H5N1-positive samples collected between July and September 2005, to 95 per cent of samples for April-June 2006.
Guan Yi, a virologist and professor of microbiology at the University of Hong Kong who led the research, said that the new strain is unlikely to be caused by viral mutation.
Instead, it is probably a previously unidentified strain that is becoming dominant, facilitated by the compulsory poultry vaccination.
"The existing H5 avian vaccines are not able to prevent infection by this virus as efficiently as they do with other types of H5N1," Guan told SciDev.Net, adding that he hopes to cooperate with the Chinese authorities to fight the new viral strain.
The findings underline how difficult it is to control the H5N1 virus as different strains can become dominant in a short time.
Strains used in poultry vaccination against this virus should be assessed and, if needed, updated on a regular basis, says Guan.
However, Zheng Shijun, of Beijing-based China Agricultural University, said that more laboratory, field tests and experiments are needed before reaching the conclusion that the new strain can resist the H5N1 vaccine in poultry.
"It is also possible that poultry could have strong natural resistance to this new viral strain so that there are no reports of massive outbreaks," Zheng says.
Millions of poultry have been culled and 14 people have died in China as a result of H5N1 infection.
The first wave of H5N1 outbreaks occurred in late 2003 and spread to many parts of Asia. The second wave began in China's Qinhai Lake in May 2005 and spread to Europe, Africa and the Middle East.
Reference: Proceedings of the National Academy of Sciences doi: 10.1073/pnas.0608157103 (2006)