Could global warming be contributing to the resurgence of malaria in the East African Highlands?
A widely-cited study published a few years ago said no, but new research by an international team that includes University of Michigan theoretical ecologist Mercedes Pascual finds that, while other factors such as drug and pesticide resistance, changing land use patterns and human migration also may play roles, climate change cannot be ruled out.
"Our results do not mean that temperature is the only or the main factor driving the increase in malaria, but that it is one of many factors that should be considered," Pascual said. The new study is slated to be published online this week in the Proceedings of the National Academy of Sciences.
After being nearly or completely eradicated in many parts of the world, malaria still affects hundreds of millions of people worldwide and has been on the rise in some highland regions and desert fringes. Because the life cycle of the mosquito that transmits malaria and the microorganism that causes the disease are extremely sensitive to changes in temperature, some scientists have speculated that rising average temperatures may be making conditions more favorable for mosquitoes and pathogen development, leading in turn to the surge in malaria cases.
But a 2002 study found no significant changes in average temperature in the highlands of East Africa, where malaria has become a serious public health problem, prompting its authors to dismiss the malaria-climate link. Not all scientists were convinced, however, and the topic has been hotly debated over the past four years.
Pascual revisited the question, using updated temperature data and improved analysis techniques. The result?
"I did find evidence for an increase in temperature, which the authors of the previous paper said was not there," Pascual said. The increase was small---half a degree over the period from 1950 to 2002---but using a mathematical model, Pascual and coworkers showed that even such slight warming could have biological consequences.