Understanding How A Diverse Environment Has A “Dilution Effect” On Disease

dilution_effect.jpgRecent research conducted by scientists at the University of South Florida indicates that keeping a high level of biodiversity in our forests and other wild environments (Northeastern U.S. and the Amazon basin in South America) may lower our risk of catching animal-born diseases.

The study, published in the Proceedings of the National Academy of Sciences, reports that by buckling down on conservation we may in fact be saving ourselves from a variety of illness and disease, some of which are quite deadly (does Ebola ring a bell!?) 

How is this possible? As it turns out, many a human pathogen had its humble beginning inside another type of animal. Picture this: a lone tick or mosquito starts hankering for a bite to eat and begins to feed on a mouse that happens to be carrying a disease. Before you know it, that same insect vector has feasted on a person, thus transmitting the virus, bacterium, or protozoan to our bloodstream. A gloomy and all-too-common scenario. 

But here’s the thing, not every pathogen is at home in every type of animal. For example, West Nile Virus prefers to spend its days dwelling inside birds before mosquitos transfer it to humans, just as Lyme disease prefers small mammals (chipmunks and mice) before ticks carry it over to people. This may not sound like particularly good news, but it is.

A recent NPRarticle explains:

The dilution effect suggests that increasing biodiversity—such as the number of different mammal species or bird species—will offer infection control, naturally. The idea is that when there's a lot of different kinds of species around, there might be fewer that make good hosts for pathogens. And when the right host is around, the other species could crowd it out and keep its numbers lower.”

In order to test this theory, the team of researchers led by David Civitello conducted a meta-analysis of over 200 reports on disease and biodiversity. In most cases, more diversity meant less infection in animals—hence fewer pathogens to pass on to humans. Deer mice, for example, living in a much less diverse area were much more likely to harbor hantavirus than animals living in areas with more biodiversity.

A similar study focusing on conservation efforts in the Brazilian Amazon found that well-preserved areas were linked to lower rates of certain diseases. A recent article in The Atlantic expands on this:

The researchers found that land-use policies are linked to noticeable health outcomes. The building of roads is associated with lowered acute respiratory infections and diarrhea—likely because of the access to healthcare they provide—but increases in malaria. Deforestation leaves more places for mosquitoes to breed, which could explain why roads are linked to more malaria.”

Knowing this, the question then becomes, would it be possible to cultivate better health (lowering the risk of disease) by protecting the environment? So far, all signs point to YES!

ILLUSTRATION: Frits Ahlefeldt-Laurvig via Flickr


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