THANGATHI, KENYA -- The boy was feverish, vomiting, and wouldn't eat. His mother rushed him to a village clinic, suspecting measles, typhoid or one of the other usual childhood ailments found in Kenya's central highlands.

Instead, the doctor diagnosed a disease she knew little about: malaria.

Though it is Africa's biggest killer, malaria has always been a regional blight. In the secluded coffee-farming villages around Mt. Kenya, malaria was rare, something other people had to worry about, in the sun-baked west or along the steamy coast.

"When I was growing up, we never heard of malaria," said Charity Njuki, 31, whose 2-year-old son, Eric, recently contracted the mosquito-borne parasite that causes the disease. Her older children, ages 14 and 10, hadn't had it. "I was really surprised."

The emergence of malaria makes Thangathi, a tiny town about 60 miles north of Nairobi, one of the new fronts in the global struggle with a changing climate, as villagers here grapple with the effects of rising temperatures.

Industrialized nations, including the United States and China, account for the vast majority of carbon dioxide emissions blamed for warming the planet, but poorer countries, particularly in Africa, are the most vulnerable to its effects, experts say.

Worldwide temperatures rose 1.3 degrees Fahrenheit during the last 100 years, but recent studies suggest temperatures in Africa are climbing faster. In Kenya's western highlands, maximum annual temperatures over the last 20 years are up about 1.8 degrees, according to Kenya's Centre for Global Health Research.

Fifteen years ago, malaria couldn't reach Thangathi, perched at nearly 6,000 feet amid steep, coffee-covered mountains. The 1970 national atlas declared the region "malaria-free," thanks to cool weather year-round, with temperatures often dipping below 65 degrees -- too cold for the strains of anopheles mosquito that carry malaria.

Today, however, malaria beats AIDS, stomach parasites and skin infections as a cause of illness here, said Peter Mbugua, regional medical officer for Nyeri district, which includes Thangathi. Since 2001, his malaria caseload has nearly doubled, reaching 206,369 last year; the disease's prevalence in the region is now second only to pneumonia.

"The situation changed very quickly," Mbugua said. "Malaria became a concern all of a sudden."

A noticeable warming

In Thangathi, most residents are unaware of the international concerns over global warming, but many say they have noticed subtle weather changes over the last generation.

Thanks to increased sunshine, corn seems to grow faster, maturing in three months rather than four. Last summer, temperatures were so high that the flowers on passion fruit trees burned.

David Gachanja, 42, who grew up in Thangathi and runs a private clinic, recalled his parents bundling him in a sweater and coat during the cold, wet month of June. This June, he sent his children to school in light jackets and short pants, thanks to temperatures in the mid-70s.

"It's ever-hot," said Boniface Maina, the local tribal chief. He said the region was experiencing other weather changes, such as longer rainy seasons and occasional showers during traditionally dry months.

At the government health dispensary in Thangathi, that has meant a steady rise in malaria cases. Clinic officials are uncertain about the exact number because they lack a simple blood test, available in many other parts of the country, that can confirm the disease in less than half a hour. The private clinic nearby has the test, but most villagers can't afford the 70 cents it costs.

In the early 1990s, if a local doctor came across a case of malaria, it almost always involved a person who had traveled to the lowlands. But in recent years, scientists and health officials have repeatedly confirmed that anopheles mosquitoes are working their way up the slopes of Mt. Kenya, thriving at higher altitudes than ever before.

Willis Akhwale, head of Kenya's Anti-Malaria Control Division, cited a number of factors for the emergence of malaria in the central highlands, including higher temperatures, increased mobility of the population and land-use changes, such as channeling of rivers and irrigating crops, which can create stagnant pools where mosquitoes breed.

Mosquito biology