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Since 1999, this world authority on influenza at St. Jude Children’s Research Hospital in Memphis, TN, has been conducting a large-scale study, sponsored by the NIAID, to investigate changes in key avian (bird) flu strains in Southeast Asia. By tracking emerging flu strains in aquatic birds, domestic poultry, and other species in key Asian countries, Dr. Webster is keeping a watchful eye on those strains most likely to cause a global pandemic. His hope is that information he and his colleagues collect will enable health officials better prepare for the inevitable.
Of utmost concern to Dr. Webster is H5N1, a particularly dangerous influenza strain that has proven fatal in roughly 60 percent of the human cases so far. In 2004, H5N1 has caused outbreaks in domestic poultry in eight countries: Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, Viet Nam, and Malaysia.
More worrisome, it has infected people in Thailand and Viet Nam. “This is very alarming, because H5N1 has learned new tricks,” he says.
Recently, Dr. Webster and colleagues found strong evidence that H5N1 is undergoing antigenic drift (antigenic drift illustration), indicating that it has made a long-term home for itself in Asia. In viruses isolated from live poultry markets in Hong Kong and key Chinese provinces from 2000 to 2004, the researchers found variants of the H5N1 virus that could be traced to the virus that emerged in Hong Kong in 1997. These variants led to the emergence of a dominate H5N1 strain in chickens and ducks that was responsible for the 2003-2004 outbreak.
“H5N1 is becoming endemic in Asia, meaning it will continue to be a problem to human health,” he cautions.
Another concern is that H5N1 strains are becoming increasingly deadly, even to aquatic birds, the natural reservoir for influenza viruses. “Before, wild ducks and shorebirds could carry these viruses and experience no disease,” he says. “What’s changed is that viruses have evolved in domestic poultry and these viruses are now killing ducks.”
In addition, the discovery of H5N1 in some dead migratory birds, such as herons, sparrows, and pigeons, leads Dr. Webster to ask if the same H5 viral strain that is infecting poultry and people may be infecting wild migrating birds of the world, which could significantly increase the chance for a pandemic. To help answer this question, he and his research team are working with Canadian wildlife officials to test ducks migrating south from Canada.
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Last Updated March 23, 2010