Less Species = More Disease

A new study connects biodiversity loss with a rise in infectious diseases

"The extinction of plant and animal species can be likened to emptying a museum of its collection, or dumping a cabinet full of potential medicines into the trash, or replacing every local cuisine with McDonald's burgers," writes Joshua E. Brown in a recent University of Vermont press release about "Biodiversity Loss Affects Global Disease Ecology," a new study that published in the December issue of the journal BioScience.

But there is another worrisome effect of the global loss of biodiversity: The decline in species means that we may be more susceptible to contracting a disease.

"Habitat destruction and biodiversity loss," -- driven by the replacement of local species by exotic ones, deforestation, global transportation, encroaching cities, and other environmental changes -- "can increase the incidence and distribution of infectious diseases in humans," write University of Vermont biologist Joe Roman, EPA scientist Montira Pongsiri and seven co-authors of the study.

The scientists give the spread of Lyme disease as an example.

Ticks get the bacterium by feeding on many species that act as hosts -- but the best host is the white-footed mouse.

In "species-poor places" devoid of larger predatory mammals, the mouse thrives. And when it does, so do the ticks that can transmit the bacterium to humans.

The effect is clear: The probability of humans contracting Lyme disease is increased in regions that are losing species.

And considering the rapid global spread of viruses that got their start locally -- such as West Nile virus -- biodiversity loss in one area doesn't mean that the attendant increase in infectious disease won't become a worldwide phenomenon.

Noting that a third of the bird species on the planet are at risk of extinction and a quarter of the mammals, Roman says, "We have an incredible amount of habitat being destroyed, along with climate change. We should expect to see the impacts of these changes occurring now, to people -- and we do."

GET INVOLVED

• Support the International Union for Conservation of Nature (IUCN) Countdown 2010 to save the world's biodiversity
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image: Deer tick (Ixodes scapularis), vector for Lyme disease (image: Wikimedia)