Quotes of the Day

Scott Tind Simmons was at his office in Phnom Penh, Cambodia, when he started to feel sick. By the time he got to bed, his flu-like symptoms gave way to achy joints and feverish dreams. That's when he got suspicious that he had dengue fever, the mosquito-borne virus that, in its deadly form, causes blood to seep from the bloodstream into tissue and eventually from the body's orifices. Several days later, doctors diagnosed the expat aid worker with a milder, non-lethal variation of the disease. Since there are no drugs or vaccines for dengue, Tind Simmons did what some 38,500 infected Cambodians did this year: he drank plenty of water and waited for his bout of "bone-break fever," as the disease is often called, to go away.

But dengue isn't going away. Across Southeast Asia, doctors and public-health officials are grappling with alarmingly high dengue-infection rates. Cambodia and Vietnam reported double the cases this year compared with last, and more than 400 deaths; Thailand and Burma each recorded roughly a third more cases in 2007. The World Health Organization (WHO) says this is the fourth consecutive year of unusually high rates in the region — and doctors are worried that global warming may be partially to blame.

That's because the mosquito that infects most people with dengue, the striped Aedes aegypti, does better in warm, wet weather. Regions experiencing rising temperatures and longer rainy seasons are seeing large outbreaks year after year, and what has previously been thought of as a tropical disease is popping up in more temperate regions. Nepal and Bhutan saw their first cases in recent years, as did isolated spots such as Easter Island. Today, an estimated 2.5 billion people live in areas where dengue is endemic. The WHO expects millions more will be added in coming years. "Dengue is an evolving situation," says Dr. Jai Narain, director of communicable diseases for the WHO in Southeast Asia. "A lot of people say climate change will impact [the disease] somewhere down the line. But it already is."

Weather isn't doing the job alone. As more and more people migrate to cities, they create additional opportunities for the mosquito to spread the virus. The problem is particularly acute in developing countries, where inadequate utilities mean residents must store water in jars and tanks — prime breeding grounds for the Aedes aegypti. Increasing air travel is also a factor as infected fliers spread the disease quickly worldwide. "It's simplistic to suggest that the increasing outbreak is solely caused by climate change," says Simon Hales, a senior research fellow at New Zealand's University of Otago. "But those who would suggest that it has nothing to do with it are equally misguided." Hales estimates that if global warming advances as predicted by the U.N., more than half the world could be dengue country before the end of this century.

Lacking vaccines or effective treatments, public-health officials are battling the disease with old-school tactics: pest control and education. But fumigation campaigns are too expensive for many Asian governments to carry out effectively; it's also difficult to regularly send out health officials to remind communities to keep their homes dry and water supplies clean. Even wealthy Singapore, a model of dengue control, was floored by an outbreak in 2005. Reported cases went down the following year, but are back up again slightly in 2007. "That's a kind of warning to us," says Hales. "As the temperature continues to increase, it gets progressively more difficult to prevent the disease from spreading — even with the best technology."

Health-care professionals are trying to raise global awareness of the threat. In Cambodia, for example, more funding goes to controlling avian flu, a disease that affects far fewer people but has a higher fear factor worldwide. Health organizations such as the U.S.-based Centers for Disease Control and Prevention are stressing the link between climate change and disease, hoping to get more money to fight mosquito-borne illnesses. "This is a critical moment," says Dr. Maria Neira, director of the WHO's program on public health and the environment. "If the public pressure is maintained, the politicians will act accordingly." Waiting for dengue fever to burn itself out may be the only option for individuals who catch the disease, but that's a lousy prescription for the planet.

• Krista Mahr