STEVE INSKEEP, host:
Ever since the 1970s there's been a steady stream of new diseases. Think of some of the famous names - Ebola, AIDS, bird flu, SARS, West Nile. That raises a question, whether the rate of new infections is increasing, or if it just seems that way.
Some researchers, writing in the journal Nature, have come up with an answer, and NPR's Richard Knox has it.
The researchers scoured the scientific literature back to 1940. Over seven and a half decades, they counted 335 new infectious diseases. The number increased steadily with a sudden peak in the 1980s. Marc Levy of Columbia University says the peak was probably due to the large numbers of Africans who were infected with HIV by then.
Dr. MARC LEVY (Columbia University): In the '80s, you had millions of people suddenly with suppressed immune systems; therefore a bunch of new diseases took root.
KNOX: In the 1990s, the number of emerging diseases fell back by a quarter, but the overall curve is steadily up. Peter Daszak heads the Consortium for Conservation Medicine at the Wildlife Trust.
Dr. PETER DASZAK (Wildlife Trust): We can for the first time definitively say that emerging diseases are increasing over time. One thing's for sure; they're on the rise, so in the next decade we can expect more emerging diseases.
KNOX: The study also uncovers some important patterns. For instance, about two-thirds of all emerging infections since 1940 have gone from animals to humans, and most of those were from wild, not domestic, animals.
The researchers say wild animal infections pose the biggest risk of new emerging diseases. Even though Daszak is one of the world's leading experts in wildlife diseases, he was surprised.
Dr. DASZAK: Everybody talks about emerging diseases that come from wildlife, and we know that a few key ones do, like Ebola, and you know, they can be very scary diseases. But I didn't expect that emerging diseases from wildlife would be increasing over time.
KNOX: The researchers say that's because human populations are encroaching more and more on wildlife habitat. That gives an opportunity to whatever viruses and bacteria lurk in the animals. Kate Jones of the London Zoological Society says the analysis gives conservationists like her a powerful new argument.
Ms. KATE JONES (London Zoological Society): The conservation voices have always been downplayed in the development community. This shows that there is a cost to development and it may be cost-effective to keep wild areas wild, that it may stop the next emerging disease coming from those areas.
KNOX: It doesn't mean that development should stop, Jones says, but more attention should be given to those hot spots that the researchers say are ripe for new infections to emerge, and buffer zones should be maintained between humans and wildlife.
Animal diseases aren't the only threat. About 20 percent of new diseases are resistant bacteria that result from overuse of antibiotics. The hotspots for these are zones of increasing population growth, places like India, Pakistan and Bangladesh, where people are getting just enough money to buy over-the-counter medicines. Daszak says the group's research provides a tool to do something about emerging diseases.
Dr. DASZAK: You know, this isn't a complete doom and gloom scenario. Sure, emerging diseases are increasing, but here we have a potential strategy to start to deal with them.
KNOX: The starting points are those hotspots the researchers have identified. Daszak says that's where scientists should focus their attention.
Richard Knox, NPR News.
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