Mixed up
hybrid CDC scientists tested the H5N1 flu (above) and a human influenza virus.
GOPAL Murti / VISUALS UNLIMITED
experts have long feared that if a virus and human influenza strain H5N1 avian influenza currently circulating in much the world were to combine their genes, the result could be a disaster-- a deadly virus that spreads easily among people. But scientists at the Centers for Disease Control and Prevention (CDC) reported today that several of these hybrid viruses are, at least in ferrets, relatively benign.
Since 1997, the H5N1 virus has infected at least 231 people mostly in Asia, 133 of them died ( science NOW, February 9). So far the virus has not taken a form that passes easily between humans. This could occur if the H5N1 slowly developed the necessary changes, as probably happened with the Spanish flu of 1918 ( Science NOW, October 5, 05). Or H5N1 virus that infected a person could exchange some of its eight genes with those of a human flu virus - keeping its hemagglutinin (HA) surface protein, to which people have no immunity. Known as reassortment, this process led to two milder flu pandemics in 1957 and 1968.
Thus, CDC researchers and colleagues used a technique called reverse genetics laboratory to make combinations of H3N2 , a strain of human seasonal flu, and the virus strain H5N1 1997. to model the spread of the virus in people, they housed ferrets inoculated with reassortant in adjacent cages to healthy ferrets so that animals may transmit the virus through the air.
The hybrid proteins with H3N2 outside and H5N1 internal proteins well replicated in the cells, but not as easily transmitted among ferrets as H3N2 itself, the CDC team found. And potentially the most dangerous combinations - viruses containing genes for surface proteins of H5N1 and the virus proteins internal human flu - not only did not increase, and the H5N1 virus, but does not spread at all between ferrets. All reassortant would probably need, reports the CDC team today more genetic changes, such as those who made the 1957 and 1968 strains most able to bind to epithelial cells of the human respiratory tract in Acts of the national Academy of sciences . "The picture is more complex" than just the mixing of avian genes and flu, says co-author Jacqueline Katz of CDC.
This does not mean that the world can let down his guard against the H5N1 virus. "I'm cautious about using the word" reassuring, "said CDC Director Julie Gerberding reporters Friday, noting that the study only looked at simple combinations of a human flu virus and one strain H5N1. But it would have been bad news if a so-called reassortant had spread easily among ferrets, according to virologist Albert Osterhaus of the Erasmus Medical Center in Rotterdam, the Netherlands. We can be a "little" relieved, he said.
For wider coverage, please stay tuned for August 4 issue of Science.
Related site
- CDC facts on H5N1
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