ROBERT SIEGEL, HOST:
Recently on NBC's "Meet The Press," the president said if the U.S. does not act, the Ebola virus could spread more widely through Africa and beyond.
(SOUNDBITE OF TV SHOW, "MEET THE PRESS")
PRESIDENT BARACK OBAMA: There's the prospect then that the virus mutates. It becomes more easily transmittable. And then it could be a serious danger to the United States.
SIEGEL: Scientists know that the Ebola virus has been mutating during this epidemic. Currently it's known to spread only through contact with bodily fluids. NPR's Nell Greenfield Greenfieldboyce reports on whether it's possible for Ebola to change in ways that would make it as contagious as a cold or the flu.
NELL GREENFIELDBOYCE, BYLINE: I asked infectious disease experts if Ebola could acquire mutations that would let it start spreading through the air between people. And they basically said we don't know. But is this a scenario that we really need to be thinking about? The answer to that one depends on whom you ask.
Michael Osterholm is director of the Center for Infectious Disease Research and Policy at the University of Minnesota. He's worried that Ebola will become much more contagious.
MICHAEL OSTERHOLM: This is a real concern. And it's one for which we can't tell you it will or won't happen. But it surely is a possibility.
GREENFIELDBOYCE: He says when this virus spreads between people and reproduces, it copies its genetic code in a sloppy way, creating genetic changes with unpredictable effects.
OSTERHOLM: We may have had more Ebola virus transmission between people in the last four to six months than we've had in the last 500 to 1,000 years. So this virus is really undergoing major mutational changes in this hyper-evolutionary period.
GREENFIELDBOYCE: Osterholm says he doesn't know how likely it is that Ebola could start spreading through the air. But the fact that it's possible creates an urgent need to stop this outbreak.
OSTERHOLM: Because a respiratory-transmitted Ebola virus for the world would be an absolute catastrophic event.
GREENFIELDBOYCE: He points to laboratory evidence that suggests this kind of virus might be capable of passing through the air. For example, pigs infected with Ebola somehow gave it to monkeys housed in the same room without touching them. But another study found no evidence of transmission through the air from infected monkeys to other monkeys.
Gary Kobinger worked on both of these animal studies. He's with the Public Health Agency of Canada. I asked him how likely it was that Ebola will mutate and start spreading more easily between people.
GARY KOBINGER: You know, that would be very speculating on what can happen or cannot happen. But I can tell you this has not happened in the past in any of the outbreaks.
GREENFIELDBOYCE: He says from one outbreak to the other, scientists haven't seen a lot of variation in this virus, suggesting there may be limits to how much it can change and still be able to infect humans. Other virologists say an airborne Ebola virus might be a theoretical possibility. But it doesn't keep them up at night.
VINCENT RACANIELLO: I'd say it's highly unlikely that Ebola virus would be able to do that.
GREENFIELDBOYCE: Vincent Racaniello is a virologist at Columbia University in New York. He says in people this virus has always been transmitted through contact with the bodily fluids of an infected person.
RACANIELLO: I don't know of any human virus that has switched from being transmitted by contact to aerosol in as long as we've been studying viruses - you know, just over 100 years.
GREENFIELDBOYCE: Think of HIV. Think of hepatitis C. There've been millions of infections. These viruses still only spread through body fluids. Why should Ebola be different?
RACANIELLO: I don't think we need to worry about this. I think right now we need to focus on stopping the epidemic and treating the people who are infected. And that in itself is a huge job.
GREENFIELDBOYCE: As things stand, this outbreak is expected to last for months. The World Health Organization estimates that some 20,000 people will likely become infected. Other predictions say it will be far more and that's with the virus spreading in the same way it always has. Nell Greenfieldboyce, NPR News.