Malaria, one of the world’s most persistent public-health challenges, is shifting its geographic footprint.
A new study informed by earlier projections of where malaria may emerge among children suggests that climate change is reshaping the disease’s distribution across Africa. Data reported July 29 in Nature indicate a gradual move from West and Central Africa toward eastern and southern regions, consistent with a warming climate.
Rising temperatures could make conditions less favorable for malaria-carrying mosquitoes in West and Central Africa while creating more suitable environments in the east and south, said Romaric Odoulami, a climatologist at the University of Cape Town in South Africa. “Malaria transmission and mosquitoes’ life cycle are very sensitive to temperature,” he said.
This represents a shift in the geographic distribution of an ancient disease. Malaria has historically been most common in West and Central Africa, where temperatures support both the parasites of the genus Plasmodium and the Anopheles mosquitoes that transmit them. Previous laboratory studies have found that mosquito-borne malaria transmission peaks at 25°C, declining below 19°C and above 34°C. Higher-elevation areas of East Africa and coastal southern Africa have been cool enough to limit widespread transmission, keeping the disease concentrated in major hotspots such as Nigeria and the Democratic Republic of the Congo.
However, an analysis of century-long blood-sample datasets from sub-Saharan Africa shows that this pattern is changing. Odoulami and his colleagues used the data to build a computer model connecting childhood malaria prevalence with temperature and precipitation, then compared their results with a counterfactual model that excluded climate change.
The team found that from 1901 to 2014, climate change likely produced a net 0.5% increase in malaria transmission across sub-Saharan Africa—one additional case for every 1,000 children—with a substantially larger rise in eastern and southern Africa. In the Ethiopian highlands, for example, malaria increased by eight cases per 1,000 children. In parts of West Africa, transmission declined by 1% to 2%, equivalent to roughly four fewer cases per 1,000 children.
The researchers project that, under an intermediate global warming scenario of 2.7°C, malaria transmission across sub-Saharan Africa could decline by 2% over the next 85 years.
Despite those climate-driven changes, malaria transmission is strongly affected by public-health interventions, which can have a greater impact than climate change alone, said Cyril Caminade, a climatologist at the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy. He emphasized the need to expand measures such as bed nets, insecticide treatments and preventive malaria drugs in areas where transmission is expected to rise.
“Africa in general lacks the luxury to wait for the key global emitters to do what is needed to reduce climate change impacts on the most vulnerable,” Odoulami said. “It’s important for regions across Africa to increase awareness of the danger of malaria where there is little knowledge of it.”
