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On the way back from a morning run up the mountain on Koh Phangan island, Natalie Revie felt something was wrong. It was not just fatigue. "I felt my back had collapsed. Any strength or power I had there was gone completely," recalls Revie, a freelance writer from England who lives in Thailand. "I felt my legs and hips belonged to a dingly, dangly scarecrow."

Revie, 30, stayed in bed the rest of the day, but she went from bad to worse. Her bones were aching all over, and she was unable to move. The stabbing pains behind her eyes were so terrible that she couldn't look at anything. Revie went to see a doctor the next day and had some blood tests that confirmed her initial worry: she had dengue.

Dengue fever, sometimes called breakbone fever, has long been endemic in Asia, especially in the tropical areas. Transmitted by the striped Aedes aegypti and Aedes albopictus mosquitoes, it affects hundreds of thousands of people in the region each year, both in rural and urban areas. This year, the number of infections is reaching highs across the continent. Thailand's dengue cases are the highest in five years, with 57,000 infections between January and August — nearly double the figure from the same period last year. The Philippines has already recorded the most cases in its history, with more than 62,000 infections reported in the first eight months of this year — a nearly 90% increase from the same period last year — and 465 people killed. In Vietnam, more than 42,000 cases were recorded before September, 60% of which were in the rainy months of July and August. There were 31,500 reported cases in Malaysia, 24,000 in Sri Lanka and 80,000 in Indonesia in the first eight months of this year.

Dengue, according to the World Health Organization (WHO), is the most rapidly spreading mosquito-borne viral disease in the world. It infects between 50 million and 100 million people annually, with 500,000 cases of the more severe infection known as dengue hemorrhagic fever. It causes 22,000 deaths every year, mainly among children and young adults. More than 2.5 billion people, or two-fifths of the world's population, live in the dengue-endemic countries, including those in Africa, the eastern Mediterranean and the Americas. The Caribbean countries are battling a wave of dengue epidemics this year. As of early September, more than 80,000 cases have been reported, overwhelming the region's hospitals and medical care.

In Asia, the disease is getting worse. "Dengue cases have increased dramatically in recent decades, especially in Southeast Asia and the Western Pacific," says Dr. Terhi Heinasmaki, the International Federation of Red Cross and Red Crescent Societies' Asia-Pacific health coordinator. The number of cases in the WHO's Southeast Asia region surged nearly 70% from 152,448 in 2004 to 257,882 in 2009. In the international health body's Western Pacific region, there were 242,424 cases in 2009, up 50% from 160,823 in 2004. Experts say that increased travel has helped mosquitoes spread dengue — and its four different strains of virus — further afield to infect greater numbers of people. Some also blame climate change, arguing that warmer temperatures have increased the number of potential breeding areas for mosquitoes. Despite being a historically tropical disease, dengue is now emerging in Himalayan countries such as Nepal and Bhutan. As the rainy season in some areas becomes longer, the longer is the period the Aedes mosquitoes — which flourish in the wet months — can thrive and multiply. "Climate change is not the only explanation for the increase of dengue, but it can contribute," Heinasmaki says.

Because Revie's condition was not deemed by her doctor to be serious, she did not require hospital treatment and she rode out the illness at home. "The first few days were awful," she recalls. "I was wracked with fever." She felt hot and cold, alternately bathed in sweat and shaking with chills. The mother of one stayed in bed for about a week in a mosquito net to prevent from her being bitten by mosquitoes and spreading the disease to her family. It took her another month to fully recover. Revie, who blogs at My Jungle Life, later heard that some local clinics had told parents that their sick children didn't have dengue because one or two symptoms didn't match. But "when the kids got blood tests at an international hospital, it was surely dengue. It was scary," she says.

With quick diagnosis and prompt, correct treatment, the fatality rate from dengue hemorrhagic fever can be reduced from around 20% to only 1%, but recognizing it's dengue, with its different variations, can be tricky. According to Dr. John Ehrenberg, the WHO's director for combating communicable diseases, there are six classic infection signs of dengue: high fever, muscle and joint pains, general feeling of malaise, pain behind the eyes, skin rashes and bleeding. "But not all cases develop these symptoms," he says. "Some may be confused with other febrile illnesses or go unnoticed together." And what those signs are may be shifting, says Dr. Lenny Santiago-Angeles, who works for the Bulacan Medical Center's pediatrician department near Manila and treats a dozen children and adolescents who are coming down with dengue each day. "The patterns of dengue are also changing. The fever may go on for a week and it disappears and later returns."

Unlike malaria, there are no drugs to prevent or specifically treat dengue. The most effective prevention is getting rid of the Aedes mosquitoes and their breeding grounds, but most governments in the region have been criticized for not doing enough. They largely resort to insecticide fumigation, which creates a false sense of security because it kills only adult mosquitoes that happen to be around, while the multitude of larvae in the breeding sites escape and take to the air within days. "Fogging activities are not necessarily effective," the WHO's Ehrenberg says. "Dengue cannot be eliminated, but it can be controlled. Elimination of breeding sites is essential in dengue control, and it requires strong community involvement."

That lack of action on what was formerly a local problem is starting to have global implications. In New Delhi, where more than 2,200 dengue infections have emerged this year, the WHO has warned the number will peak in October, just as 8,000 athletes from 71 countries descend onto the Indian capital for the Commonwealth Games. The threat of dengue also looms over the Asian Games, to be held in November in Guangzhou and other neighboring cities. Chinese health authorities have issued a warning after Dongguan, one of the games' venues, reported a minioutbreak in mid-September.

Yet preventing this disease is surprisingly simple. One crucial action is raising the public awareness and making sure people keep their premises clear of stagnant water. Experts recommend getting rid any water receptacles, from flowerpots to unused tires — anything that can serve as potential mosquito breeding grounds. (Singapore, which has been lauded for its prevention program, goes as far as fining residents $150 if mosquitoes are found breeding their property.) Dengue may be becoming a global disease, but efforts to control it actually begin in one's own home and backyard.

• Yenni Kwok
• As rates of the mosquito-borne illness spike, local governments need to do more to contain the potentially fatal disease