Disease runs riot as species disappear

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Disease runs riot as species disappear

01 July 2009 by Debora MacKenzie

Magazine issue 2715. Subscribe and get 4 free issues.

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COULD biodiversity protect humans from disease? Conservationists have long

suspected it might, and now they have the evidence to back this up.

 

Keeping complex ecosystems intact is thought to pay big dividends, by preserving

natural balances among species that keep animal diseases in check. These

includes zoonoses - animal diseases that affect humans.

 

Rodents in the Americas carry hantaviruses, which can be lethal to people who

inhale them from dried droppings. Some 500 people a year in the US die after

being infected with the " sin nombre " hantavirus (SNV) from the common deer

mouse.

 

Laurie Dizney and colleagues at Portland State University in Oregon put four

different kinds of live traps in five parks around Portland over four years. In

each park, they found variation in both the number of mammal species and the

proportion of deer mice with SNV. The less mammal diversity there was, the more

deer mice were infected (Emerg Infect Dis, DOI: 10.3201/eid1507.081083, in

press). In the park with the lowest diversity, infection levels were sky-high.

 

" This is a landmark paper, " says Peter Daszak, head of the Wildlife Trust in New

York, which investigates biodiversity and disease. It is hard to test how the

two affect each other, he says, partly because of the huge amount of fieldwork

involved.

 

As a result, Lyme disease is the only zoonosis that has been shown to be limited

by biodiversity. It is spread by ticks, and the more mammal species there are,

the more often ticks bite species that don't transmit Lyme.

 

Unlike Lyme disease, hantaviruses spread directly between the animals they

affect. " This is the first time anyone has shown anything like this in a

directly transmitted disease, " says Daszak. Dizney suspects that the more mammal

species there are, the closer mice stick to their home territories, as many of

the mammals are predators, so mice encounter and infect each other less often.

The team hopes this link between human health and biodiversity could boost

public support for conserving diverse ecosystems.

 

Daszak cautions that the effect may not hold true for other zoonoses. " Losing

biodiversity may promote this virus because deer mice are a 'weed' species that

thrives in depleted environments, " he says. " But it is also true that the more

species there are, the more zoonoses there may be. "

 

 

 

 

 

" Hobbes: Do you think there's a God? Calvin: Well, SOMEBODY'S out to get me. "