Genetic analysis of swine flu virus finds new mixture of diverse parts: H1N1 may be amenable to future vaccine development.
A detailed genetic analysis, published online May 22 in Science, pinpoints the origins of each of the virus's components. Many have been circulating in human and swine populations for years, but the new H1N1 virus combines the bits and pieces in a way never before seen. The analysis suggests that current vaccines probably won't provide protection from the virus, but that it is susceptible to some antiviral drugs and will be amenable to new vaccine development.
A study of the Virus's neuraminidase protein (the Nin H1N1),published May 20 in Biology Direct, also shows that the virus is sensitive to some drugs but that parts of the protein important for vaccine development and antibody therapies are already changing.
Pigs are the likely origin of the virus, says Nancy Cox, chief of the influenza division at the Centers for Disease Control and Prevention in Atlanta and a coauthor of the paper in Science. But it is still unclear whether the virus jumped directly from pigs to humans or infected an intermediate host first.
CDC has sent candidate virus strains for vaccine development to several U.S. manufacturers, says Anne Schuchat, CDC's interim deputy director for the science and public health program. Though the number of new cases in the United States is falling, Schuchat says, the virus is still active in pockets of the country. "We don't want people to think we're out of the woods yet," she says. "It could come back in the fall in the worst way."
Genetic analysis of the H1N1 virus reveals that three of its genes, including the hemagglutinin gene (the H in H1N1), originally came from the 1918 Spanish influenza virus and have been present in pigs ever since. The genes have not changed much, probably because pigs do not live long enough to get reinfected with the same virus, Cox says.
Now that the H1N1 swine flu virus has entered humans, researchers expect it to mutate at the same rate as currently circulating seasonal influenzas.
The new virus does not contain the genetic changes thought to have helped the 1918 flu virus and the H5N1 avian flu virus adapt to humans, the researchers report. That means that other genetic components of the new virus must be responsible for its ability to pass from person to person. Both studies find that the closest relative of H1N1's neuraminidase gene is from a Eurasian swine flu virus that probably leaped from birds to pigs in about 1979.
The new virus has a different amino acid from both the H5N1 virus and the 1918 Spanish flu (also an H1N1 virus) in 21 of 387 investigated positions on the protein, researchers from Singapore's Agency for Science, Technology and Research report in the study in Biology Direct. Viruses isolated from patients during the first two weeks of the current outbreak already have changes on the outer surface of the neuraminidase protein that could interfere with antibodies against the virus or b alter the effectiveness of future vaccines. But none of the changes have altered the parts of the protein targeted by antiviral drugs, such as Tamiflu or Relenza.
Flu protein in 3-D
This image shows H1N1 swine flu's neuraminidase protein. Yellow depicts regions where the new virus differs from H5N1 avian flu and 1918 H1N1 Spanish flu. Red depicts mutations that occurred in the first few weeks of the 2009 outbreak. Green shows the antiviral drug zanamivir bound to the protein.
Swine flu's mix
The H1N1 swine flu virus combines bits of different influenza viruses that have been circulating for a long time. Chart shows gene segments and their origins.
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|Title Annotation:||Genes & Cells|
|Author:||Saey, Tina Hesman|
|Date:||Jun 20, 2009|
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