Malaria, one of the world’s most prominent public health challenges, is on the move.
A new study based on previous predictions of where malaria in children may appear suggests that climate change is redrawing the map of malaria’s spread across the African continent. The data, reported July 29 in Nature, show a gradual shift from West and Central Africa toward the eastern and southern regions, consistent with global warming.
Increased temperatures may mean a more hostile environment for disease-carrying mosquitoes in the West and Central regions and a more favorable climate in the eastern and southern regions, says 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 says.
This represents a shift in the map of this ancient disease. Malaria has historically been most prevalent in West and Central Africa, where temperatures are suitable for both the parasite that causes the disease (the genus Plasmodium) and the mosquitoes that carry it (the genus Anopheles). Previous laboratory studies have shown that mosquito-based transmission of malaria peaks at 25° Celsius, while it drops off below 19° C and above 34° C. High-elevation regions of East Africa and coastal southern Africa have been cold enough to fend off significant malaria transmission, centering the disease in hotbeds. including Nigeria and the Democratic Republic of the Congo.
But a deep dive into blood sample datasets from sub-Saharan Africa spanning over a century reveals that this story is changing. Odoulami and colleagues used the data to build a computer model linking childhood malaria prevalence to temperature and precipitation, then compared their findings with a hypothetical model without climate change.
The team found that from 1901 to 2014, climate change has likely caused a net 0.5 percent increase in malaria transmission across sub-Saharan Africa — one excess case for every 1,000 children — with a much greater increase in East and southern Africa. In the Ethiopian highlands, for example, the spread of malaria increased by 8 cases per 1,000 children, and in parts of West Africa, transmission rates decreased by 1 to 2 percent — about four fewer cases per 1,000 children. By the researchers’ calculations, climate change is predicted to lower malaria transmission rates in sub-Saharan Africa by 2 percent over the next 85 years with an intermediate warming scenario of 2.7° C globally.
Despite what the climate data show, malaria transmission is largely influenced by control efforts, which outweigh climate-induced changes in their impact, says Cyril Caminade, a climatologist at the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy. Caminade says that it will be important to expand mitigation strategies including mosquito bed nets, insecticide treatments and malaria prevention drugs to areas where malaria transmission is projected to increase.
“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,” says Odoulami. “It’s important for regions across Africa to increase awareness of the danger of malaria where there is little knowledge of it.”