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High-flying insects expand Ethiopia’s malaria zone

June 23, 2017, by Tim Radford

The mosquito’s gradual invasion of higher altitudes increases malaria risk.
Image: By Wormke-Grutman via Wikimedia Commons

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In a warming world new opportunities open up for disease-bearing mosquitoes, spreading Ethiopia’s malaria zone to higher altitudes.

LONDON, 23 June, 2017 – For the malaria parasite, things are looking up. As climates change, and mountain regions warm, conditions become favourable not just for the parasite but for the mosquito that carries it. New research suggests that Ethiopia’s malaria zone could soon include the highlands, for centuries free of the disease’s ravages.

In a new study in Environmental Research Letters US scientists say they looked at a detailed set of data for Ethiopian temperatures between 1981 and 2014 and identified a significant increase in the altitudes at which the thermometer went above 15°C and 18°C.

The first is the minimum air temperature at which the parasite Plasmodium vivax can survive. The second is the threshold temperature for Plasmodium falciparum. These two parasites are responsible for most of the malarial incidence in Ethiopia.

“The elevation at which the temperature thresholds are met has risen by more than 100 metres since 1981. While a 100-metre increase may appear modest, we estimate that more than six million people currently live in areas with statistically significant increases in threshold temperature,” said Bradfield Lyon, of the Climate Change Institute of the University of Maine, who led the study.

Mosquitoes prosper

Malaria killed 429,000 people worldwide in 2015. The World Health Organisation estimates that 212 million suffered from the disease. That doesn’t mean more people in Ethiopia are going to sicken and die from one of the world’s great scourges.

But it does mean that the conditions for the survival of the parasite, and the Anopheles mosquito that carries them, are improving.

For most of human history the Ethiopian highlands – where most of the people live – have been protected by the temperature from malarial hazard.

But global warming as a consequence of the prodigal combustion of fossil fuels, with ever higher ratios of greenhouse gases in the planetary atmosphere, suggests that this protection may not endure.

“We estimate that more than six million people currently live in areas with statistically significant increases in threshold temperature”

The concern is not new, and not confined to the African high terrain. The malarial parasite and its carrier, the mosquito, are sensitive to temperature, and so researchers have been using global temperature data to track the advance of the disease.

Health experts have repeatedly warned that with changes in temperature and precipitation, dangerous and lethal tropical infections have greater opportunities to spread. Malaria was once endemic in southern Italy (the name derives from mal aria, Italian for “bad air”) and as Europe warms, it becomes once again potentially hospitable to old diseases and new, such as dengue feveralso carried by a mosquito species.

Health authorities need to know when circumstances change sufficiently to favour the host insects, and the parasites and infections they carry. So meticulously maintained temperature readings matter not just to climate science, but to governments and health services at every level.

“Until quite recently, undertaking this type of study was not possible owing to a lack of quality controlled and sufficiently high spatial resolution climate data,” Professor Lyon said.

“These new data allow us to examine the climate of the highlands in much more detail and confirm some of the anticipated changes of a warming Earth.” – Climate News Network

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