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 鈥� 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 鈥渟in nombre鈥� hantavirus (SNV) from the common deer mouse.
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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, , ). In the park with the lowest diversity, infection levels were sky-high.
鈥淭his is a landmark paper,鈥� says Peter Daszak, head of the 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鈥檛 transmit Lyme.
Unlike Lyme disease, hantaviruses spread directly between the animals they affect. 鈥淭his is the first time anyone has shown anything like this in a directly transmitted disease,鈥� 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. 鈥淟osing biodiversity may promote this virus because deer mice are a 鈥榳eed鈥� species that thrives in depleted environments,鈥� he says. 鈥淏ut it is also true that the more species there are, the more zoonoses there may be.鈥�
