Scaling the Heights

Andrew Githeko grew up in Kenya's Central Highlands, about 5,700 feet above sea level. His village was untouched by malaria; the altitude made it too cold for the mosquitoes that carry the disease. Not anymore. These days, intermittently, the disease can be found in and around his home village. Githeko, 50 years old, is a vector biologist in charge of the climate and human health research unit at the Kenya Medical Research Institute in Kisumu. He is also one of the 2,000 scientists of record on the Intergovernmental Panel of Climate Change (IPCC), which shared the 2007 Nobel Peace Prize with Al Gore.

 In 2006, a scientist dispatched by Githeko found larval evidence of the malaria carrier Anopheles arabiensis at an elevation of 6,300 feet on Mt. Kenya, the first finding at that altitude. The glaciers that straddle the 17,000-foot colossus are visibly receding, but Githeko was taken aback by the rate at which the mosquito is scaling its heights. Climate change holds the potential to profoundly affect epidemiologic patterns, and Githeko says malaria is particularly sensitive to this upheaval.

Because arthropods cannot regulate their body temperature, ambient temperature changes have a direct effect on metabolic and development rates of the mosquito, whose larvae cannot survive at temperatures below 57 degrees Fahrenheit. Below 61 degrees the development of the Plasmodium parasite is also severely delayed, to the extent that it will not fully mature in a mosquito's lifespan. Warmer temperatures speed up larva and parasite development, and cause adult mosquitoes to take more blood meals -- all of which increase the mosquito's capacity to spread the disease. What's more, so-called fringe areas -- regions that are relatively malaria-free but prone to situational flare-ups -- are vulnerable to epidemic outbreaks, since residents have little or no immunity.

Global temperatures may rise by anywhere from 2 to 12 degrees Fahrenheit over the course of this century. Even at the low end the change will powerfully influence the demographics of malaria. Moreover, the IPCC expects climate variability to increase, a recipe for continued epidemics in the highlands. Githeko and his colleagues have created forecasting models that factor planetary warming into the dynamics that determine malaria outbreaks. Anticipating the time and location of an epidemic can help authorities target medications, bed nets (of which Githeko is a fan), and insecticide campaigns.