Second strain of bird flu found, say scientists
By Jim Loney in Atlanta, Georgia
March 22, 2006
THE H5N1 bird flu in humans has evolved into two separate strains, a development that will complicate the search for a vaccine and the prevention of a pandemic, US researchers say.
The genetic diversification of the pool of H5N1 avian influenza viruses with the potential to cause a human influenza pandemic heightens the need for careful surveillance, researchers said on Monday at the International Conference on Emerging Infectious Diseases in Atlanta.
"Back in 2003 we only had one genetically distinct population of H5N1 with the potential to cause a human pandemic. Now we have two," said Rebecca Garten of the US Centres for Disease Control and Prevention, who helped conduct the study.
One of the strains, or clades, made people sick in Vietnam, Cambodia and Thailand in 2003 and 2004 and the second, a cousin of the first, caused the disease in people in Indonesia in 2005. Two clades may share an ancestor but are genetically distinct - as are different strains of the AIDS virus, the team from Atlanta found.
"This does complicate vaccine development. But we are moving very swiftly to develop vaccines against this new group of viruses," said Nancy Cox, chief of the centres' influenza branch.
The H5N1 strain of bird flu has spread across Europe, Africa and Asia, and infected about 180 people, mainly in South-East Asia, killing nearly 100, since it re-emerged in 2003.
People can become infected if they come into close contact with infected birds. Scientists fear the virus could mutate into a form that could pass easily between humans, triggering a pandemic in which millions could die.
All influenza viruses mutate easily and H5N1 appears to be no exception. But Dr Cox said the evolution of a second clade did not move the virus closer to human-to-human transmission.
The US Health and Human Services Department has already recognised the two strains and approved the development of a second H5N1 vaccine based on the second clade.
US Government officials said on Monday that it was "increasingly likely" that bird flu could be detected in the US this year, but added it might not mean the start of a human pandemic.
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March 22, 2006
THE H5N1 bird flu in humans has evolved into two separate strains, a development that will complicate the search for a vaccine and the prevention of a pandemic, US researchers say.
The genetic diversification of the pool of H5N1 avian influenza viruses with the potential to cause a human influenza pandemic heightens the need for careful surveillance, researchers said on Monday at the International Conference on Emerging Infectious Diseases in Atlanta.
"Back in 2003 we only had one genetically distinct population of H5N1 with the potential to cause a human pandemic. Now we have two," said Rebecca Garten of the US Centres for Disease Control and Prevention, who helped conduct the study.
One of the strains, or clades, made people sick in Vietnam, Cambodia and Thailand in 2003 and 2004 and the second, a cousin of the first, caused the disease in people in Indonesia in 2005. Two clades may share an ancestor but are genetically distinct - as are different strains of the AIDS virus, the team from Atlanta found.
"This does complicate vaccine development. But we are moving very swiftly to develop vaccines against this new group of viruses," said Nancy Cox, chief of the centres' influenza branch.
The H5N1 strain of bird flu has spread across Europe, Africa and Asia, and infected about 180 people, mainly in South-East Asia, killing nearly 100, since it re-emerged in 2003.
People can become infected if they come into close contact with infected birds. Scientists fear the virus could mutate into a form that could pass easily between humans, triggering a pandemic in which millions could die.
All influenza viruses mutate easily and H5N1 appears to be no exception. But Dr Cox said the evolution of a second clade did not move the virus closer to human-to-human transmission.
The US Health and Human Services Department has already recognised the two strains and approved the development of a second H5N1 vaccine based on the second clade.
US Government officials said on Monday that it was "increasingly likely" that bird flu could be detected in the US this year, but added it might not mean the start of a human pandemic.
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