60秒科学:森林的过度砍伐导致痢疾在巴西肆掠（在线收听）

A 4 percent decrease in forest was associated with a nearly 50 percent rise in malaria cases in western Brazil.

You know saving the rainforest is good for biodiversity. But it may also be a boon to human health. That's because less clear-cutting may mean less malaria, according to a paper out this week in the journal Emerging Infectious Diseases.

Researchers looked at stats for 2006 from 54 health districts in western Brazil. The sites had more than 15,000 cases of malaria. The investigators compared those cases to deforestation in the same health districts over the previous 10 years. They found that a loss of just four percent of forest cover was associated with nearly 50 percent more malaria cases. And malaria risk was highest five to 10 years after the jungle was cleared.

Not all mosquitoes carry malaria. But the human-loving species Anopheles darlingi does, and previous studies have shown that it thrives in disturbed areas. In fact, you're over 200 times more likely to find one of them biting you in a clearing than you are deep in the jungle, where other more benign species compete with them for blood.

So how much clear-cutting is too much? We don't know yet—but an intact swath of rainforest appears to provide free public health services.