The Origins of the Next Pandemic

Zoonotic pathogens passed from wildlife to people, from lowest occurrence (green) to highest (red).

Photo: Nature

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The next deadly outbreak of disease is likely to originate in a pathogen that jumps from wildlife to humans in a poor nation before spreading around the world.

The path of diseases from wildlife to humans is nothing new. The flu originated in birds (which is why concerns about a virulent avian influenza are so acute). Other examples include HIV, SARS and Ebola.

The authors of a new study, who mapped the global hotspots for wildlife disease, say that the encroachment of humans into wild areas is the heart of the problem. But the tendency for rich nations like the U.S. to over-medicate is leading to the evolution of drug-resistant bugs, another worrying concern for future outbreaks.

Here's how Columbia University described the new research:

Despite three decades of research, previous attempts to explain these seemingly random emergences were unsuccessful. In the new study, researchers from four institutions analyzed 335 emerging diseases from 1940 to 2004, then converted the results into maps correlated with human population density, population changes, latitude, rainfall and wildlife biodiversity. They showed that disease emergences have roughly quadrupled over the past 50 years. Some 60% of the diseases traveled from animals to humans (such diseases are called zoonoses) and the majority of those came from wild creatures. With data corrected for lesser surveillance done in poorer countries, “hot spots” jump out in areas spanning sub-Saharan Africa, India and China; smaller spots appear in Europe, and North and South America.

“We are crowding wildlife into ever-smaller areas, and human population is increasing,” said coauthor Marc Levy, a global-change expert at the Center for International Earth Science Information Network (CIESIN), an affiliate of Columbia University’s Earth Institute. “The meeting of these two things is a recipe for something crossing over.” The main sources are mammals. Some pathogens may be picked up by hunting or accidental contact; others, such as Malaysia’s Nipah virus, go from wildlife to livestock, then to people. Humans have evolved no resistance to zoonoses, so the diseases can be extraordinarily lethal. The scientists say that the more wild species in an area, the more pathogen varieties they may harbor. Kate E. Jones, an evolutionary biologist at the Zoological Society of London and first author of the study, said the work urgently highlights the need to prevent further intrusion into areas of high biodiversity. “It turns out that conservation may be an important means of preventing new diseases,” she said.

About 20 percent of known emergences are multidrug-resistant strains of previously known pathogens, including tuberculosis. Richer nations’ increasing reliance on modern antibiotics has helped breed such dangerous strains, said Peter Daszak, an emerging-diseases biologist with the Consortium for Conservation Medicine at the Wildlife Trust, another Earth Institute affiliate, who directed the study. Daszak said that some strains, such as lethal variants of the common bacteria e. coli, now spread widely with great speed because products like raw vegetables are processed in huge, centralized facilities. “Disease can be a cost of development,” he said.

The group’s analyses showed also that more diseases emerged in the 1980s than any other decade—likely due to the HIV/AIDS pandemic, which led to other new diseases in immune-compromised victims. In the 1990s, insect-transmitted diseases saw a peak, possibly in reaction to rapid climate changes that started taking hold then. Team members soon hope to study this possibility and its future implications.

Daszak says the study has immediate uses. “The world’s public-health resources are misallocated,” he said. “Most are focused on richer countries that can afford surveillance, but most of the hotspots are in developing countries. If you look at the high-impact diseases of the future, we’re missing the point.” Team members say nations must share more technology and resources in hotspots to reduce risk. “We need to start finding pathogens before they emerge,” said Daszak.

In addition to the ZSL and Earth Institute researchers, the study was coauthored by John L. Gittleman, dean of the Odum School of Ecology, University of Georgia.

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