Human Infectious Diseases and Species Extinction

Scientists are discovering that species extinctions fuel the rise and spread of infectious diseases and hinder medical research.

The Rutgers study is just one of many new investigations into the link between biodiversity and human health. “The natural world provides so many services vital to our health,” says Eric Chivian, founder and director of Harvard Medical School’s Center for Health and the Global Environment. “But these services depend on an enormous diversity of species about whose interactions we know very little.”

Over the past decade, the Harvard center has been working with three United Nations agencies to draw together what scientists do know. In 2008, it published Sustaining Life: How Human Health Depends on Biodiversity. The 542-page tome draws on the research and expertise of more than 100 scientists. But rather than a dry academic text, it takes the form of a richly illustrated coffee table book with chapter authors writing in language accessible to a general audience as well as their fellow scientists. “Above all,” Chivian explains, “we’re trying to reach beyond specialists to help everyone grasp the urgencies involved in species loss.”

Diversity and Disease
Imagine a newly hatched tick resting on the floor of a northeastern U.S. forest, waiting for its first blood meal. If the larval tick is in a fragmented or otherwise degraded patch of woods, the first host it encounters will probably be a white-footed mouse.

As a result, the tick will likely become infected with the Lyme disease microbe, Borrelia burgdorferi. In much of the United States, up to 80 percent of white-footed mice carry this disease-causing bacterium, which they pass to deer and humans via the bite of infected ticks.

Now consider the same newly hatched tick in an undisturbed forest. Here its first host is more likely to be an opossum, raccoon, ground bird, lizard or other non-mouse host. None are good carriers of the Lyme disease bacterium. As a result, the tick will likely escape infection and never transmit the disease to anyone.

In 2000, animal ecologist Richard Ostfeld described this Lyme disease-blocking dynamic and dubbed it the “dilution effect.” In essence, he explains, the greater a habitat’s biodiversity, the more likely that an animal-borne microbe such as B. burgdorferi will end up in a dead-end host—one that does not pass it along. Read the entire article.

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