Health

Researchers Alter the Contagiousness of a Virus

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Researchers around the world are trying to figure out exactly what makes a virus highly contagious. A new report in the journal Science describes one way to turn a contagious virus into one that is much more difficult to transmit.

SCOTT SIMON, host:

This is WEEKEND EDITION from NPR News. I'm Scott Simon. Flu researchers have done an important experiment. It's reported in this week's issue of the journal Science. They've taken a replica of the virus that touched off the flu pandemic of 1918 and made just two tiny changes in it. Those changes switched it from a highly contagious virus to one that wasn't. NPR's Richard Knox reports the experiment could have implications for what may be the most urgent question in science. What does it take for a flu virus to go pandemic?

RICHARD KNOX: Some researchers say the best way to answer that question is to look at the worst pandemic virus ever - the one from 1918. It exists in a couple of high security labs. Scientists reconstructed it out of genetic fragments taken from people who died nearly 90 years ago. Terrence Tumpey works with the 1918 replica at the Centers for Disease Control and Prevention.

Mr. TERRENCE TUMPEY (Centers for Disease Control and Prevention): We think that this is an ideal virus to study better understand viruses that had this pandemic potential.

KNOX: Tumpey and his colleagues infected ferrets with the virus. Of all mammals, they're closest to humans in their susceptibility to flu. Sure enough, the infected ferrets died. So did ferrets in the next cage. Then the scientists modified the spiky protein that sticks our from the virus's coat. The virus was still lethal, but there was a big difference.

Mr. TUMPEY: In the cages next to those particular ferrets, the contact ferrets were fine. There was no signs of disease and no signs of spread. So that was quite striking. I didn't think it would be that simple.

KNOX: One reason the nearby ferrets didn't die is that the ferrets infected with the mutant virus didn't sneeze. The reason they didn't sneeze is apparently this. By changing just two molecules in the virus's code, scientists prevented it from infecting cells in the animal's nose and throat. This raises a disturbing question. Could such slight changes turn a relatively non-contagious virus into something dangerous? In particular, scientists wonder if today's H5N1 bird flu virus is just a couple of mutations away from becoming the next pandemic killer.

Mr. PETER PALESE (Mount Sinai Medical School): And I think the answer to that is no. In my opinion, this is not possible, or not easily possible.

KNOX: That's Peter Palese of Mount Sinai Medical School. He's a co-author of the new paper. He notes that over the past three years, H5N1 has killed no more than 160 people. So if that virus could have gone pandemic easily, it would have by now. He says it might take many more than just two genetic changes. Still, Palese thinks there may be other viruses out there with the potential to go pandemic, such as the virus that caused a mild human pandemic in 1968 and then retreated to birds. But Tumpey thinks researchers should keep an eye out for the two key changes that made the 1918 virus so contagious. If they pop up in the Asian bird flu virus, he says, alarm bells should sound. Richard Knox, NPR News.

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