7 MARCH 2003VOL 299SCIENCEwww.sciencemag.org1504CREDIT:VINCENT YU/APNE W SFO C U SAn Avian Flu Jumps to PeopleWhile researchers monitor U.S. pigs for potentially dangerouschanges in swine influenza virus (see main text), recent events onthe other side of the world have sounded an even more urgentalarm. Last month in Hong Kong, a 33-year-old man died and his9-year-old son fell seriously ill after contracting an avian influenzavirus from a source that remains mysterious. Initial genetic sequencing suggests that the virus may be de-scended from one found in wild birds. If so, it could be difficult tocontain. In all previously known cases of an avian flu jumping tohumans, the source is believed to have been poultry. But “this virushasn’t been seen in domestic poultry,” says Robert Webster, direc-tor of the World Health Organization’s (WHO’s) collaborating lab-oratory on animal influenza at St. Jude Children’s ResearchHospital in Memphis, Tennessee. However, authorities have notruled out the possibility that the virus came from chickens on a rel-ative’s farm in mainland China.Most flu viruses are adapted for a particular group of animals,although pigs can mix and match viruses from birds and humans.And on seemingly rare occasions, flu viruses have jumped thespecies barrier from other animals to humans. The last two humaninfluenza pandemics, or worldwide flu epidemics, were caused byviruses that incorporated both human and avian flu genes. Becausehumans have no immunity to many strains of avian influenza, such
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