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Bird Flu Virus May Need Significant Mutation for Human Pandemic
posted by admin on 02/08/06
The H5N1 bird Flu News, July 31, 2006 (Bloomberg)
Scientists failed in multiple attempts to make a more contagious form of the H5N1 bird flu, suggesting the virus may have to undergo massive change to cause a human pandemic.
After mixing genes from human and bird influenzas in a way researchers have projected might lead to a pandemic, the virus remained hard to spread said researchers led by Taronna Maines, a U.S. Centers for Disease Control and Prevention scientist. The study was conducted on ferrets, which are at least as susceptible to flu as people, the scientists said in a report released today.
The H5N1 virus is known to have killed 134 people, most of them through contact with birds, and might kill millions more should it becomes contagious, researchers have said. Scientists believe the risk of a pandemic will increase as the virus spreads more widely and an animal or a human became infected with both H5N1 and a human flu strain at the same time.
``The acquisition of human flu virus genes into H5N1 didn't make it more transmissible,'' said Peter Palese, a Mt. Sinai School of Medicine microbiologist in New York who studies influenza and wasn't involved in the research, in a telephone interview. ``It appears the virus would need significant mutations to transmit easily in people.''
The research will help disease-trackers understand one of the most important questions in flu research, the genetic changes necessary for a virus to spread in humans, said CDC's Jacqueline Katz, a co-author on the study. In a process called reassortment, human and bird strains can exchange genes, leading to a hybrid virus better adapted to human spread.
While the study suggests that H5N1 may not be close to becoming a pandemic virus, health officials can take nothing for granted, CDC director Julie Gerberding said in a telephone call with reporters.
``I'm cautious about using the word `reassuring,''' she said. ``This does not mean that H5N1 can't develop into a pandemic strain. We are far from out of the woods on H5N1 on a global scale.''
Hybrid viruses were probably responsible for pandemics that occurred in 1957 and 1968. While neither killed more than 2 million people, both strained health systems with high rates of illness.
The so-called 1918 Spanish flu that killed 50 million people also probably started out as a bird virus, U.S. researchers said in October. It might have gained its infectious capability through another route, by evolving specific gene mutations that enabled it to jump directly from birds into humans, Katz said.
Ability to Spread
Katz and her co-workers combined genes from H5N1 with those of a common human flu virus, called H3N2. The researchers infected caged ferrets with the combinations to see whether the hybrids were able to spread from one group to another when the animals coughed or sneezed.
H3N2 spread easily among the cages just as it does in schools, churches, subways and other public places. Hybrids with H5N1 weren't able to spread.
The hybrids also didn't spread any more easily when they were taken from infected animals and passed on to other animals, Katz said.
The work was done in a highly secure biosafety level 3 laboratory to ensure that no humans were infected with contagious hybrids, Katz said.
H5N1 was first discovered spreading in birds in 1996, when the virus was found on a goose farm in China. After 18 people were infected the following year, the virus was out of sight until 2003, when it began spreading through poultry flocks and a human death was reported in Vietnam.
After having spread for 10 years in birds, it's possible that H5N1 may not gain the same contagious ability that the Spanish flu did, Mt. Sinai's Palese said.
``The easy mutations have been made, and they haven't worked,'' to help the virus spread in people, he said. ``But can you exclude it from being a human threat? You can't exclude it.''
Katz's group used a virus isolated from a patient in 1997. The researchers will continue to study more versions of H5N1 and more hybrid combinations to gain a better understanding of how that might happen, she said.
``It's a complex procedure for a virus to acquire the property of transmissibility,'' Katz said. ``This process isn't simple.''
-- Editor: Gienger
To contact the reporter on this story:
John Lauerman in Boston at email@example.com.
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