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