Study: As Biodiversity Declines, Tropical Diseases Thrive (NPR)

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Global health advocates often argue that the tropical diseases that plague many countries, such as malaria and dengue, can be conquered simply with more money for health care – namely medicines and vaccines.

But a new paper is a reminder that ecology also has a pretty big say in whether pathogens thrive or die off. Using a statistical model, researchers predicted that countries that lose biodiversity will have a heavier burden of vector-borne and parasitic diseases. Their results appear this week in PLoS Biology.

"The general logic is that the more organisms you have out there, the more things there are that can interrupt the life cycle of disease, and the less concentration you'll have of any vector," says Matthew Bonds, a researcher at Harvard Medical School and the lead author of the paper.

But plants, mammals and birds are disappearing fast – one-third of the world's species are now threatened with extinction, according to the United Nations. And when the creatures that prey on mice, mosquitoes or other vectors of disease go, parasites and other disease-causing agents discover it's a lot easier to survive.

Scientists have already shown that's one reason for the explosion of Lyme disease in the Northeast United States. A 2002 paper in the Proceedings of the National Academy of Sciences found that if you have a rich community of tick hosts, like squirrels, mice and other small mammals, the disease is diluted among them. But if the habitat is degraded, and ticks carrying Lyme have only white-footed mice as hosts, the disease risk to humans can rise dramatically.

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