"This [means] that H5 avian vaccines are not able to prevent infection by this virus as efficiently as they do with other types of H5N1."
Scientists fear that the new strain may have arisen in response to over-reliance on the sole existing bird flu vaccine.
"It is not surprising that H5N1 continues to evolve," said Hon Ip, a diagnostic virologist at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin, who is not affiliated with the new research.
"It is a virus that is looking for opportunities, and this is a good example of how, if there is a weakness, Mother Nature somehow is going to exploit it."
The appearance of the new strain in urban locations is particularly troubling to virologists, who fear that the vaccine-resistant virus could ignite a pandemic if it mutates to become easily transferred from human to human.
"If you have a situation with large numbers of poultry that are poorly vaccinated, close human-to-poultry contact, and infected birds moving around the country—you're just asking for additional viruses to evolve," Ip said.
So far no evidence has been found to suggest that any strain of H5N1—including the Fujian-like type—can be passed easily from human to human.
But the University of Hong Kong's Guan fears the rapid spread of the strain may still pose a threat.
"We think that this virus is likely to have already instigated a third wave of H5N1 infection in this region, as it is already widespread in southern China and has also been detected in other neighboring countries," he said.
"However, as of yet, we do not have any evidence that it is causing widespread infection outside of our surveillance area."
Asian heath care officials may have to modify their anti-bird flu systems in order to prevent the new strain from sweeping through the region's poultry populations and posing potential problems for human health.
"Current control measures are ineffective in dealing with the evolutionary changes that H5N1 undergoes," Guan said.
"This study also suggests that reliance on a single vaccine against H5N1 over a number of years, which is currently practiced, is unlikely to adequately control this disease in poultry."
USGS's Ip echoes Guan's belief that a vaccination program by itself is not a complete solution.
"I think that in this particular case the authors make a convincing argument that the vaccine may not be the best match against the virus in circulation," he said.
"You need to have a comprehensive program that monitors which flocks are infected and deals with them, stops the movement of infected animals, and provides timely access to information."
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