U.S. researchers announced Monday that the much-feared H5N1 strain of avian influenza has in fact split into two strains. "Back in 2003 we only had one genetically distinct population of H5N1 with the potential to cause a human pandemic," Rebecca Garten, of the Centers for Disease Control and Prevention, told an infectious-diseases conference in Atlanta. "Now we have two."
The two strains are linked, and share the same genetic background, but are distinct from each other. The first was the strain that emerged in Thailand, Vietnam and Cambodia between 2003 and 2004, causing the first wave of human infections to garner media attention. The second strain is that which caused a number of infections in Indonesia in 2004.
Both strains are still active, and either could be the one to spark off the human avian influenza pandemic the world is nervously awaiting.
"As the virus continues its geographic expansion, it is also undergoing genetic diversity expansion. ... Only time will tell whether the virus evolves or mutates in such a way that it can be transmitted from human to human efficiently," Garten said
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