An international team of scientists has proven there is a direct link between climate change and the incidence of malaria. It shows that tens of millions of people living in highlands in East Africa and South America are at risk of the disease as global temperatures warm.
The idea that warmer air would allow the parasite to survive at higher altitudes along with the mosquitoes that transmits it between humans has been around for two decades said Dr Menno Bouma.
"It was never proven. A lot of research came out but it couldn't make the connection and so the link between climate and malaria was lost. Global warming was a non-issue for malaria," said Dr Bouma who is based in Ireland but is honorary senior lecturer at the London School of Hygiene and Tropical Medicine.
Common sense however continued to argue in favour of the theory. It held that malaria would creep to higher altitudes during warmer years and then shift to lower elevations in cooler years. This is because both the Plasmodium parasites that cause it and the Anopheles mosquitoes that spread it both thrive in warmer air, Dr Bouma said.
Researchers at the London School of Hygiene and Tropical Medicine which began the work 20 years ago persisted however and joined up with researchers at the University of Michigan.
They examined malaria case records from western Colombia recorded between 1990 and 2005 and others from the Debre Zeit area of central Ethiopia from 1993 to 2005. Dr Bouma and colleagues were looking at the spatial distribution of malaria cases that seemed linked with temperature variations in highland regions.
This finally delivered a clear signal, with cases showing a strong connection to temperature changes. They publish their findings this morning in the journal Science .
This now raises difficult issues, Dr Bouma said. Global warming “will creep up the mountains and spread to new high-altitude areas”, he said. “And because these populations lack protective immunity they will be particularly vulnerable for severe morbidity and mortality.”
The Debre Zeit region alone has about 37 million people living in rural areas at risk of a wider spread of malaria due to warming. Previous work estimated that one degree temperature increase could result in an additional three million malaria cases each year in Ethiopian children.
“This is indisputable evidence of a climate effect,” said Dr Mercedes Pascual from the University of Michigan. It meant that sustained efforts were needed to try and control the spread of the disease.
