U. FLORIDA (US)—Global warming is expected to have little effect on the spread of malaria, largely due to current control efforts and development, according to a new study.
Scientists and public policymakers have been concerned that warming temperatures would create conditions that would either push malaria into new areas or make it worse in existing ones.
But a team of six scientists analyzed a historical contraction of the geographic range and general reduction in the intensity of malaria and determined that if the future trends are like past ones, the contraction is likely to continue under the most likely warming scenarios. Details of the study appear in the journal Nature.
“If we continue to fund malaria control, we can certainly be prepared to counteract the risk that warming could expand the global distribution of malaria,” says David Smith, an assistant professor at the University of Florida.
Malaria control efforts over the past century have shrunk the prevalence of the disease from most of the world to a region including Sub-Saharan Africa, Southeast Asia, and South America, with the bulk of fatalities confined to Africa, despite a global temperature rise of about 1 degree Fahrenheit, on average, during the same period, notes the team, part of the multinational Malaria Atlas Project.
“The globe warmed over the past century, but the range of malaria contracted substantially,” says Andy Tatem, also an assistant professor at the University of Florida. “Warming isn’t the only factor that affects malaria.”
The reasons why malaria has shrunk are varied and in some countries mysterious, but they usually include mosquito control efforts, better access to health care, urbanization and economic development.
The banned pesticide DDT was instrumental in ridding the disease from 24 countries in Southern Europe, the former Soviet Union, and elsewhere in the world between 1955 and 1969, Smith says.
Researchers debate how the U.S. defeated malaria, but the reduction of mosquito breeding grounds, improved housing and reduced emphasis on agriculture that comes with development—and the reduced risk of bites that accompanies urbanization—probably played a role, he explains.
“There is no one tale that seems to determine the story globally,” Tatem says. “If we had to choose one thing, we would guess economic development, but that’s kind of a cop out” because the specific mechanisms may still remain unclear, and controlling malaria might also help to kick-start development.
In any case, current malaria control efforts such as insecticide-treated bed nets, modern low-cost diagnostic kits and new anti-malarial drugs, have proved remarkably effective, with more and more countries achieving control or outright elimination.
Unless current control efforts were to suddenly stop, they are likely to counteract the spread of mosquitoes or other malaria-spreading effects from anticipated temperature increases, Smith says.
Simon Hay, an author of the Nature paper and one of the chief architects of the Malaria Atlas Project, notes that modern malaria control efforts “reduce transmission massively and counteract the much smaller effects of rising temperatures.”
“Malaria remains a huge public health problem, and the international community has an unprecedented opportunity to relieve this burden with existing interventions,” he says.
“Any failure in meeting this challenge will be very difficult to attribute to climate change.”
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