How MERS Made The Leap From Animals To Humans

David Quammen writes about how diseases jump from animals to people. He explains recent outbreaks of Middle East Respiratory Disease, or MERS, including three cases discovered in the U.S. this month.

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TESS VIGELAND, HOST:

The last couple of weeks have brought some pretty scary headlines about a new disease called MERS, Middle East Respiratory Syndrome. It actually first appeared in Saudi Arabia in 2012. There have been 600 confirmed cases, 173 people have died of the disease. The first confirmed case of MERS in the U.S. was discovered earlier this month in Indiana, then a second in Florida and yesterday a third case in Illinois.

This week, the world health organization said MERS is not a pandemic, at least not yet, but its transmission is speeding up. The CDC is advising Americans to wash hands frequently and avoid people who appear to be sick. David Quammen writes about viruses and epidemics. I asked him why MERS is spreading more quickly now.

DAVID QUAMMEN, SCIENCE WRITER: Well, there's a lot of speculation. Nobody knows for sure. I mean, one possibility is that the virus has adapted to better transmission from one human to another. That's a really scary possibility and there is no evidence for that so far. The other possibility might be there have been circumstances, for instance, in Saudi Arabia where more people are coming into contact with somebody who is carrying it. And a third possibility is that it's spilling over from its animal host more.

Because this virus was never seen before in humans, they know that it must be what's called a zoonotic virus, which means a virus that lives in some other species of animal and then spills over into humans.

VIGELAND: Now MERS is a respiratory illness. A lot of people have been comparing it to another highly infectious disease from about a decade ago which we all know as SARS. Are they similar?

QUAMMEN: They're similar in the sense that they both belong to the family of corona viruses. Some corona viruses are fairly innocent and innocuous. Some of our colds are caused by corona viruses. But then back in 2003, a new corona virus emerged from Southern China that was really nasty and scared the bejesus out of people. And that became known as SARS corona virus. So that when this MERS thing appeared in autumn of 2012 and they recognized it as a corona virus, that's part of what raised the level of alarm.

VIGELAND: Well, we eventually learned that SARS began in bats before it moved to humans. And you already mentioned that we are looking at some sort of animal transmission regarding MERS as well. What sets off that kind of spillover of disease from animal to human?

QUAMMEN: In a word it's opportunity. The virus gets the opportunity to spill into a new species. That opportunity occurs because we come in close contact with some species of animal that's carrying a new virus, maybe its bats, maybe its camels. People have talked a lot about camels in connection with MERS.

Humans come in, maybe they're cutting down trees, maybe they're building a timber camp, maybe they're killing and eating the wildlife. The virus spills over, gets into the first human, replicates and then if we're unlucky passes from one human to another.

VIGELAND: Well, knowing how contagious and deadly this MERS virus has been so far, what do you expect to happen going forward? Is this at all containable?

QUAMMEN: Well, it's certainly containable. We hope it's containable. SARS was containable. SARS was stopped. It infected about 8,000 people, killed about 800 and then it was contained by fast science and good rigorous public health measures. Nobody knows what's going to happen next but there's some very good people out there who have been working quickly on the science side and on the public health side. We hope that we can contain this, yes.

VIGELAND: David Quammen is the author of the book "Spillover: Animal Infections and the Next Human Pandemic." David, always enlightening and not a little bit terrifying. Thank you.

QUAMMEN: You're very welcome, Tess. Good to be with you.

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VIGELAND: This is NPR News.

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