New Bird Flu Strain Spreads Fast, Is Resistant to Vaccine
for National Geographic News
|November 1, 2006|
A newly discovered bird flu strain has emerged in China and has spread rapidly through poultry in Southeast Asia.
Human infections by the new strain have also turned up in several locations, including both farms and urban centers, intensifying fears of a worldwide flu pandemic that could kill millions. (Related: "Bird Flu Will Reach U.S. and Canada This Fall, Experts Predict" [March 14, 2006].)
Magnifying those concerns is the vaccine-selective nature of the new strain, which means that existing animal vaccines are less effective on it than they are on previously known bird flu types.
"This virus seemed to spread very fast over a big geographic region," said Yi Guan, director of the State Key Laboratory of Emerging Infectious Diseases at the University of Hong Kong in China.
A team led by Guan discovered the new strain—dubbed "Fujian-like"—while monitoring chickens, ducks, and geese in Chinese markets, including several in Fujian Province (map of China).
"However, we don't have any evidence to show whether this virus is more dangerous or less dangerous than any other H5N1 [bird flu] viruses," Guan said.
He and his colleagues report their findings in this week's issue of the Proceedings of the National Academy of Sciences.
To help prevent the spread of bird flu, China has instituted an extensive, compulsory vaccination program for chickens.
But the effort has proven unable to contain the new strain, which has displaced other H5N1 variants to become the dominant strain in the southern China surveillance area, Guan says.
The new virus accounted for 95 percent of the infected birds that Guan's team examined between April and June 2006.
"This novel variant may have become dominant ... because it was not as easily affected as other strains by the avian vaccine used to prevent H5 infection," Guan said.
"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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