Mapping 'Hot Spots' for Emerging Diseases Outbreaks of emerging infectious diseases such as Ebola, SARS, HIV and avian influenza are on the rise, researchers report in the journal Nature. They say that areas in which humans and animals come in very close contact are a key grounds for emerging diseases.
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Mapping 'Hot Spots' for Emerging Diseases

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Mapping 'Hot Spots' for Emerging Diseases

Mapping 'Hot Spots' for Emerging Diseases

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JOE PALCA, host:

This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Joe Palca. Ira Flatow is away.

Diseases such as avian influenza, Ebola and SARS have been showing up more often, but health officials may not be looking in the right places to spot the next outbreak of one of these emerging infectious diseases. That's the finding of an international team of researchers writing this week in the journal, Nature. The scientists looked at data collected over decades from hundreds of different disease outbreaks and mapped out likely hot spots where new outbreaks were most likely to occur. The team found that the developing world contains many of these hot spots. They're especially common in areas where humans and animals come in very close contact.

Joining me now to talk about the work is one of the authors of the paper, Peter Daszak, he's executive director of the Consortium for Conservation Medicine at the Wildlife Trust here in New York, but he joins me today from the campus of UCLA in Los Angeles.

Welcome back to the program, Dr. Daszak.

Dr. PETER DASZAK (Executive Director, Consortium for Conservation Medicine, Wildlife Trust, New York): Hi. Great to be here.

PALCA: Great to have you.

And also joining us is Michael Osterholm. He's director of the Center for Infectious Disease Research and Policy at - professor in the School of Public Health and an adjunct professor in the Medical School at the University of Minnesota.

Welcome back to the program, Dr. Osterholm.

Dr. MICHAEL OSTERHOLM (Director, Center for Infectious Disease Research and Policy; Professor, School of Public Health; Adjunct professor, Medical School of the University of Minnesota): Thank you, Joe.

PALCA: And if you want to join us, give us a call. Our number is 800-989-8255. That's 800-989-TALK. If you want more information about what we'll be talking about this hour, go to our Web site at where you'll find links to our topic. And you can also find us in Second Life on the SCIENCE FRIDAY island.

So, Dr. Daszak, can you give me a little background on what you were looking at - how did you go about looking for these hot spots and was that the main thrust of this work?

Dr. DASZAK: Well it's the sort of the holy grail of emerging diseases to be able to say, where is the next HIV or SARS going to emerge from. And, you know, predicting things is what we all ultimately would like to do, and it's very hard to do.

So what we're trying to do is to get as good as we could get - close as we could get to that predictive approach. We made a list of every known emerging disease of people for the last 40-50 years, build this into a database and spent a couple of years trying to target - as good as we could get it - the point origin of each of those diseases.

And then we created a statistical model where we tested various factors that are known to drive emergence, things like human population growth and wildlife diversity and whereabouts on the planet where latitude - rainfall. And just to see what correlates with emergence.

But I think the most important thing we did is we corrected for the number of people working on diseases because if you just go on what's known, you end up tracking where scientists are working…

PALCA: Yeah.

Dr. DASZAK: …rather than where disease really emerged.


Dr. DASZAK: So, once we did all that, we found a couple of - in the form of points. First, that, you know, this isn't hyped. These diseases really are on the raise. And it's statistically proven now that over time, over the last 60 years, there's been a significant rise in the number of emerging diseases every decade corrected for the number of scientist increasing every decade.

And also a couple of important groups of diseases to watch out for despite a lot of people focusing on the exciting diseases like Ebola and SARS, which I'll talk about in a minute, and drug-resistant microbes are very significant threat to global health and representing about 20 percent of the diseases that have emerged over the past 60 years. And finally the really high impact diseases tend to be zoonotic diseases that emerge from wildlife like HIV did, like SARS did.

PALCA: Zoonotic is the disease that starts off in animals and then somehow jumps to the human population.

Dr. DASZAK: Yeah, that's right. And these diseases often come from very bizarre routes like with SARS, the wildlife trade, and ultimately they probably originated in bats.

PALCA: Mm-hmm.

Dr. DASZAK: So can we predict anything by that? Well, yes. Once you create the statistical model, you can plot that on the map where the most likely origin of the next zoonosis is and it tends to be in the very high diversity areas of the tropics where there's lot of wildlife diversity and therefore a lot of potential new pathogens that wildlife carry. The more wildlife you have in the region, the more likely unknown pathogens are out waiting to emerge. And in those areas where humans are encroaching and populations are growing and clashing with wildlife there and especially where they exploit wildlife for food and for habitat, that's where we're going to see the next emerging diseases.

PALCA: Right. And so I guess the next question that springs to mind is, well, if the numbers are going up and it's not just because we're looking better, why?

Dr. DASZAK: Well, that's a very important question and it seems to me that what our paper really says is that emerging diseases are driven by us. It's the things we do to the environment, to livestock production, in wildlife trade and in our own demography, the way we grow our populations and move out into new areas that drive emergence.

And I think that, you know, this isn't a dim and gloomy message. What we're really saying is that we need to slightly change the way we're looking at emerging diseases and really take them on board as a cost of doing business, globally.

And it's a bit like, you know, whenever we think we're going to do something to the environment, we have an environmental impact assessment or maybe we also need a sort of emerging disease impact assessment and just look at what potential that would have to cause a disease to emerge and just modify the way we do things slightly.

PALCA: Okay. Mike Osterholm, what's - you know, you've worked in public health as a state official and now you're in academics. What's the importance of having this information? What does it do for you?

Dr. OSTERHOLM: Well, first of all, it helps to let the population know that what has happened is just a snapshot of what will happen in the future and that's important because we obviously need to continue to not only detect these infections early, but also do the research that goes with it and that takes resources.

And we often - in government, in academia, live by biennial budgets of state and federal agencies. And so that it's not unusual, for example, just this past year - in fact, the past month, we just had $750 million cut out of our funds needed for pandemic influenza work because of a veto by the White House.

One of the points that this makes is that in fact we have to be prepared for the future because more of these illnesses are going to occur and we can't stop working on them.

PALCA: But is there - I mean, does this paper give you any idea of maybe doing a better job of detecting them so that you don't have to worry quite so much about dealing with them if they get here?

Dr. OSTERHOLM: Well, I think, first of all, Peter's paper which was a very thoughtful approach at looking at emerging infectious diseases, I think, does give us a sense where you might want to look.

But I think also we have some new developments in the last 10 years that were not really reflected in the data of emerging infections of 20 and 30 years ago. Today, with the world of the Internet and the ability to communicate, we're finding out about these outbreaks of new emerging illnesses much quicker than we ever did before. Even in developing world countries, in the central jungles of the world, we're hearing much more about it.

If avian influenza, as we now know it, was occurring 25 years ago. Much of what whas happening in Asia would be unknown to us. Today, we're finding out about it often within hours.

PALCA: Yeah.

Dr. OSTERHOLM: So I think we are doing a better job today at finding these. But I think the point that you raised, Joe, is what can we do about it. And as Peter has pointed out, you know, this is a complex issue. And when you have the number of people we have today on the face of the earth, 6.5 billion, one out of every nine people who has ever lived since the caves is now on the face of the earth.

If you look at all the production animals we have: the cattle, the pigs, the poultry - to feed that population and then you mix that with our ever increasing encroachment on other land areas. We're cutting into the rainforest and so forth, there isn't a lot we can do in a sense of we're just going to interface these infections more and more frequently. The best we can hope for is once they start to get into the human population to try to control them or limit them as we can. And I think that's going to be an important issue.

The final piece I would just say is one of the other inevitable problems we have is that as the late Josh Lederberg once said, the famous Nobel Prize winner, who actually was one of the ones who coined the term "emerging infections," said the bugs were here before us, they're going to be here while we're here and they're going to be here after we're here.

And antibiotic resistance fits into that pattern of what Dr. Lederberg was talking about as we have microbial evolution, every 20 to 30 minutes, a new generation. And as we have used antibiotics over the past 20 to 50 years, we obviously have challenged through evolutionary pressures these microbes. And we're only going to see more of the drug-resistant infections that Peter talked about over the next 20 or 30 years and again we're all worried about that and trying to do what we can to minimize that, but that's inevitable with evolution.

PALCA: All right, let's go and listen to some of what our - what some of the listeners have to say about this and let's go first to Daniel(ph). Is it Rice Lake, Wisconsin?

DANIEL (Caller): Yeah.

PALCA: Welcome to the program.

DANIEL: Hello. Should we expect one of the consequences of global warming to be the spread of diseases into other regions, like malaria, once again endemic in the Mississippi Valley?

PALCA: Ah, interesting. Peter Daszak, what about that?

Thank you Daniel.

Dr. DASZAK: Yeah. You know, that's really the next stage in our research is what will happen when things like, you know, future trends in global warming and population growth. How will that change the dynamics of the hot spots? I think we will see infections moving into new areas. We'll see vectors that the insects that carry those infections moving into new areas. I think most people - most scientist agree with that. But I don't think places like the Mississippi Delta are going to see very large significant outbreaks because, you know, we are in a country that can afford air-conditioning and, you know, nets on the windows. And we can afford anti-malarial drugs. I think that climate change spells problems ahead for a lot of other countries that can't afford those treatments.

And you know, and I think that they're all messages to - with this sort of approach, we can target a little bit better the limited resources we've got to maybe get ahead of the curve on the countries that are going to be suffering from that.

Dr. OSTERHOLM: Now if I can add to that, I think…

PALCA: Sure.

Dr. OSTERHOLM: …an important consideration is the fact that none of us yet know what climate change is really going to do in terms of temperature or precipitation and available water. There are a number of different models out so there's no doubt that the world will warm, and it will warm significantly. But, for example, one of the most recent NASA models actually shows potential reversal of the Gulf Stream, such that instead of warm water coming up through the Caribbean and up along the northeastern part of the United States, it may reverse it because of the melting of the Artic ice cap. If that were the case, the United States may actually cool down and other parts of the world will warm up dramatically.

So one of the things that we need to do is constantly be at the top of our game with surveillance, of understanding where are these climate changes taking us, and what is happening. What is happening with precipitation? What's happening with people movement? What's happening with food supplies, meaning where are we growing food? Where are cattle at? That's going to help us predict where to look for these new emerging infections that Peter just talked about. And that's not clear yet. This is going to take a lot of work for us to stay on top of this one.

PALCA: Okay. Well, we're going to have to leave it there for a few minutes because we got to take a short break.

We're talking with Peter Daszak, the director of the - executive director of the Consortium for Conservation Medicine at the Wildlife Trust; and Mike Osterholm, he's the director for Infectious Disease Research and Policy at the University of Minnesota.

And we're going to take a short break and continue our discussion about where and when and how much emerging infectious diseases are going to affect us in the coming decades, and hopefully we'll be around to face them, I guess, is the main thing, so stay with us, we'll be right back.

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We're talking this hour about emerging infectious diseases around the world. My guest are Peter Daszak, he's executive director of the Consortium for Conservation Medicine at the Wildlife Trust in New York; and Mike Osterholm, he's director of the Center for Infectious Disease Research and Policy, a professor in the School of Public Health and an adjunct professor in the Medical School at the University of Minnesota.

And you can call us - our telephone number is 800-989-8255. That's 800-989-TALK. And let's take another call now and let's go to Ray(ph) in Phoenix, Arizona.

Ray, welcome to SCIENCE FRIDAY.

RAY (Caller): Yes. Thank you very much for taking my call.

PALCA: Sure.

RAY: My question has to do with the household pets. We have a dog and a cat and we don't let the dog come to our bedroom very muc,h but the cat seems to have a free pass all over our faces and everything at night. And I'm concerned - how does this - household pets, in general, impact this transmission of infectious diseases to human, and I'll take my answer off the phone. Thank you.

PALCA: Okay, Ray. Thanks.

Mike Osterholm, maybe.

Dr. OSTERHOLM: Well, first of all, today, all of us would tell you that companion animals are one of the best things that we can talk about in society in terms of all of the positive and sociologic benefits, so it has to be kept in mind that this is a very positive thing.

Having said that, of course, they do represent a potential avenue for new diseases getting to humans. And when you say new diseases, one of the things where you think about today, for example, is where are your pets get their food supply from. Only this past year did we understand that there was a certain chemical that was in the dog food supply that came from China, that in this case, was not something that humans had to worry about, but there was this very complex and complicated route in which this contamination got into the dog food supply, originating from China.

Today, infectious agents can be in the same way and we're working up an increasing number of outbreaks of illness where the food may have been contaminated for that pet that you bought at a pet store and therefore could transmit that onto humans.

In addition, where there are pets, you also have a potential for tick factors, meaning, ticks may come onboard your pet into your household and in some locations, that can also play a role. So in general, this is not a major source of infections to individuals, particularly in North America. Other parts of the world, one last illness is of great importance as we still have major concerns about rabies in many parts of the world.

I just came back from Thailand and worked over there. And on an average year, up to 400 people in Thailand die from rabies as a result of dog bites. So that there's still those concerns that we deal with, but fortunately, we've not had any new and major exotic emerging infectious diseases per se come from the typical companion animals.

Now the question though that I think really is one that should be addressed here - and I think Peter would agree with this - is we're seeing an increasing trade in exotic wild animals that become pets. And as a result, we are seeing other serious infectious diseases issues, emerging infections, from those Gambian rats that come from Africa or from raccoon dogs which are actually a rodent that come from China. And so that anyone buying a non-traditional companion animal like a dog and a cat, need to be very aware that there is a real risk of any number of infectious diseases. And we have a very limited handle on that problem right now as the trade in exotic animals has grown dramatically over the past two decades.

PALCA: Gambian rat, wow, okay.

Let's take another caller now and go to Ronald(ph) in Manahawkin, New Jersey.

Ronald, welcome to SCIENCE FRIDAY.

RONALD (Caller): Well, thank you. Thank you for having me. My question is what are you doing about the airports and people are taking off their shoes especially in the summertime and their feet - people have them shoes - they're all kind of - I have contracted athlete's feet that way myself. I've contacted congressmen, Homeland Security, the Center for Disease Control, newspapers and health departments. I've been working on this for four years - everybody ignores me.

PALCA: Well, it's an interesting point, Ronald. Let me ask Peter Daszak. I mean, how big of a part does air travel play in spreading these diseases around the globe.

Dr. DASZAK: Well, you know, I mean, athlete's foot is not an associative(ph) disease as some of the things we've been talking about and although it is a nuisance, air travel does, however, play a major role in driving disease emergence. It's not really that air travel is where diseases originate, but it's a great way for diseases to spread around. And either through humans that are infected get on an airplane in one region and spreading a pathogen to a completely new part of the world; or in the trade, as Michael said, the trade in wildlife which is growing every year.

Now there are dates on the global trade - global and travel, and they show pretty clearly this rising, despite the fuel costs, and it's predicted to continue to rise and in some places more than others. So I think what this does is it makes those more at risk of a pandemic from one of these emerging diseases.

What our paper really talks about is where disease will originate. Some of those diseases won't really go very far because the conditions aren't right for them to move out of that region, but when you get increased air travel, you start to project an increase in the number of pandemics that can emerge

And again, it provides a way to target a bit better, so we really should be looking seriously at the trade in wildlife. And there are very little mandated surveillance on wildlife trade even into the U.S., and even for mammals which we know carry a lot of potentially lethal pathogens. And it's not even the known. It's the unknown that trade has a potential to carry. So I think that the two aspects of air travel are pretty important for the global spread of disease. But don't worry too much about athlete's foot.

PALCA: Thank you. It's good to maintain perspective here.

We have a question from Second Life, from Bauer(ph) who says, who asks, how does the accessibility or lack of access to health care in developing regions affect the spread of diseases to the developed nations.

Mike Osterholm, any thoughts on that?

Dr. OSTERHOLM: Well, clearly, the ability of a disease to become an emerging infection means that it's relatively new in humans, and so just the ability to get health care in and of itself doesn't mean that the emerging infectious diseases are going to occur. So as we've talking about on this call, in the show here, most of the diseases that we're seeing of recent years have had a wild animal or an animal reservoir there. What happens, however, is once that disease does make the cross between the animal to human species barrier, now it is in humans and, of course, that can be a problem in and of itself in that local area.

But the ability to get out of that native population of the developing world, is in part related to, first of all, how is the agent transmitted, is it respiratory, is it blood borne, is it only in stool, how we transmit it.

The second thing is how frequently they have contact with the outside world and what does that mean in terms of - like SARS, for example. One infected physician from China stayed at a hotel one night in Hong Kong and infected a number of people that it took to three continents within days. And that was merely just being on the same floor of the hotel he was in because the air was contaminated. So that it's not directly related to the health care per se, but it surely does impact at the local area. If a new disease should happen there, how much can it be transmitted?

One example of when we were always concerned about while it gets a lot of publicity, obviously, it's not a major public health problem, but Ebola virus, is a virus that actually is transmitted via the blood-borne route. We think today that certain subhuman primates or monkeys and even bats may play a role in getting it to humans. But in the African experience, the way the big problem unfolds is in hospitals because they have one syringe or two syringes. They have two pairs of gloves and that's it. And once you have one person come in with it and they get blood contamination on these, it spreads quickly to the rest of the hospital. Those we can contain quickly, that's poor health care, but we can contain them once we know about that.

But in general, I'd say it's not really just a function of the health care per se that makes the exotic new emerging infection flame up and spread to the rest of the world.

PALCA: I think we have time for one more quick call on this topic, so let's go to Shelley(ph) in Antrim, New Hampshire.

Shelley, welcome to SCIENCE FRIDAY.

SHELLEY (Caller): Hi. Thank you.

PALCA: You're welcome.

SHELLEY: I was a little bit interested in how you feel about the limited resources using it more for prevention rather than constantly sticking fingers in the dike and stop - trying to stop this disease or that disease, educate the medical profession to stop using blood spectrum in antibiotics, breeding super resistant microbes, which you've already said account for 20 percent of emerging diseases, focus on not polluting our bodies and environment either with pollutants or stress which suppresses our immune systems and to - rather than everybody focusing on this disease or that disease, deal with our dysfunctional culture. I know it's a big thing to ask.

PALCA: Right. It's a lot to ask, Shelley…

SHELLEY: I know. I know…

PALCA: …but let me get Mike Osterholm…

SHELLEY: And as for a sociological - for animals - they have more than a sociological function, they have a physiological impact…

PALCA: Exactly.

SHELLEY: …helping to reduce stress, so whatever they might carry, I think is more than they'd hope for in the positive impact they have in helping our bodies to be strong enough to deal with diseases and fight them off…

PALCA: Excellent question. Hold on. Go ahead, Peter Daszak.

Dr. DASZAK: That depends on what you actually do with wildlife. I mean, if you trade wildlife in very dense market places and then chop them up and eat them, and you run a risk of getting infected and I don't think - I think what our paper is saying are two things. One is that exploiting wildlife and moving into other habitat has a risk attached to it of catching some pathogens that they carry. So that's a poster(ph) message because conservation efforts to protect those wildlife may also reduce the risk of emerging diseases.

Secondly, you know, the misallocation of resources is really what - if you - I agree to with you're saying essentially that we shouldn't - too often we rely on technological fixes, vaccines and drugs, and we expect that they will be available to solve our problem when it emerges. And all our paper's trying to do is to provide a way of just getting ahead of the curve a little bit and just saying let's use some of those resources that would otherwise wait to be used when the disease is emerging. Let's try and prevent it emerging in the first place. Let's increase our surveillance on things like respiratory infections, encephalitis in developing countries that look like they could be from wildlife. Let's try to investigate those averages a bit more efficiently, working with local governments. And let's try and protect wildlife areas a little bit better and let's try and just get ahead of that curve slightly.

PALCA: Okay. Well, I'm afraid that's where we're going to have to leave it.

Gentlemen, thank you both very much.

Dr. DASZAK: My pleasure.

Dr. OSTERHOLM: Thank you.

PALCA: Okay. That was Peter Daszak and Mike Osterholm. Peter Daszak is the executive director of the Consortium for Conservation Medicine at the Wildlife Trust here in New York, but he joined us from L.A. in the campus of UCLA; and Mike Osterholm is the director of the Center for Infectious Disease Research and Policy, professor at the Public School of Public Health and an adjunct professor in the Medical School at the University of Minnesota.

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