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  Yahoo News 1 Feb 07
Small changes stop flu virus spread, study finds
 By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - Two little changes in the virus that caused the 1918 Spanish flu pandemic stopped it from spreading from one animal to another, a finding that may help determine what will cause the next pandemic, scientists reported on Thursday.

Researchers who have been studying a reconstructed version of the 1918 virus found it very easy to stop it from spreading from one infected ferret to another -- although the altered viruses still quickly killed the animals.

"Work on the 1918 virus is providing clues that are helping us evaluate other influenza viruses with pandemic potential, such as H5N1, that may emerge," said Dr. Terrence Tumpey, a U.S Centers for Disease Control and Prevention microbiologist who led the study.

"With this vital research, we are learning more about what may have contributed to the spread and deadliness of the 1918 pandemic," CDC Director Dr. Julie Gerberding said in a statement.

"By better understanding how this virus spreads, we can be better positioned to slow down or stop the spread of the pandemic virus and hence be better prepared for the next pandemic."

Experts agree that a pandemic could hit at any time. The most likely suspect is H5N1 avian influenza, which is spreading among birds and has infected 270 people worldwide, killing 164 of them.

Influenza is a threat because it mutates regularly, spreads very easily and kills people. Seasonal flu kills between 250,000 and 500,000 people a year, according to the World Health Organization. Every 30 years or so, a flu virus strain will make a big mutation and suddenly become more deadly.

The 1918 pandemic, caused by the H1N1 virus, killed about 50 million people worldwide in two years.

HOPING TO AVERT PANDEMIC

H5N1 currently kills more than half its human victims but in its current form does not infect people easily. It has only been passed from person to person in extremely rare instances.

Scientists want to find out which mutations would make H5N1 pass easily from person to person so they can try to control or at leats predict a pandemic.

The CDC team rebuilt the 1918 H1N1 virus and tested it in ferrets, which become infected with influenza in much the same way that people do. Writing in the journal Science, they said through genetic engineering they made a modest change of two amino acids in the hemagglutinin protein -- the "H" in an influenza virus name -- that stopped transmission of the virus between ferrets.

This suggests that hemagglutinin, found on the surface of flu viruses, was central to the 1918 virus's ability to transmit efficiently from one person to another.

For an influenza virus to spread efficiently, it must attach better to the cells in the human upper airway instead of to cells in the gastrointestinal tracts of birds. H1N1 was a bird virus that somehow adapted itself to humans.

H5N1 is a bird virus that has not quite made this change. "Though we still don't know what changes might be necessary for H5N1 to transmit easily among people, it's likely that changes in more than one virus protein would be required for the H5N1 virus to be transmitted among humans," Tumpey said.

The researchers said the mutations that allowed H1N1 to shift from birds to people do not make H5N1 shift in the same way. "Thus, it is currently unknown which additional mutations in the H5 hemagglutinin would cause a shift to the human-type specificity," they wrote.
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