Temperature is critical to malaria's spread. A mosquito picks up the Plasmodium parasite that carries the disease when it bites an infected human, and it carries the parasite in its gut, where it matures--a process that takes about 10 to 14 days at about 25°C. At temperatures below about 16°C, the parasite doesn't mature fast enough, and the mosquito dies before it can pass it on. Temperatures above 40°C kill the parasite.
So where did scientists go wrong?
Thomas's findings were borne out by fellow panelist Mercedes Pascual of the University of Michigan, Ann Arbor. Her recent studies in the highlands of western Kenya, a relatively cool region, have revealed that a 0.5°C increase in temperature increases malaria cases an average of threefold. That means a small increase in temperature can have a large impact on the spread of malaria, she said. Pascual also said that this temperature increase could account for about one-half to two-thirds of the observed outbreaks in western Kenya since the 1970s.
Thomas's work can also improve malaria transmission models and high-resolution hazard maps, such as one presented by panelist Christopher Thomas of Aberystwyth University in the U.K. The maps use remote sensing and field data to produce site-specific estimates for infectious bites per year.
And Thomas himself hopes his data will help stem the tide of malaria transmission. "If we can better understand disease risk and the intensity of transmission," he says, "it allows us to develop a much more effective [way] to target our limited toolbox of intervention more effectively."