Lyon: Rising temps provide for conditions conducive for malaria transmission in Ethiopia

Increasing temperatures are fostering more favorable conditions for the transmission of malaria into the highlands of Ethiopia, according to a study led by University of Maine associate research professor Bradfield Lyon.

Traditionally, the cooler climate in the highlands has provided a natural buffer against malaria transmission.

But new data indicate rising temperatures over the past 35 years are eroding this natural buffer and allowing conditions more suitable for malaria to climb into highland areas, says Lyon, who is based at the Climate Change Institute and in the School of Earth and Climate Sciences.

People with malaria generally experience fever, chills and a flu-like illness. If they’re not treated, severe complications and death can result.

In 2015, the Centers for Disease control estimated 214 million cases of malaria occurred worldwide and 438,000 people died, mostly children in Africa.

The elevation at which the necessary temperature thresholds are met has risen by more than 100 meters since 1981.

“While a 100-meter increase may appear modest, we estimate that more than 6 million people currently live in areas with statistically significant increases in threshold temperature,” he says.

Malaria is a climate-sensitive disease, and while the biology of malaria transmission is complex, sufficiently low air temperatures inhibit the development of the malaria parasites that cause the disease.

Air temperatures below approximately 18 degrees C (64 degrees F) and 15 degrees C (59 degrees F), respectively, effectively stop development of the Plasmodium falciparum and P. vivax parasites responsible for the majority of malaria cases in Ethiopia, says Lyon.

Low temperatures also impede development rates and population density of the Anopheles mosquito, which transmits the disease.

Lyon’s study identified statistically significant increases in elevation for both the 18 degree C and 15 degree C thresholds in highland areas between 1981 and 2014.

“The necessary temperature conditions for malaria transmission are now being met on an increasingly regular basis at higher elevations in the Ethiopian highlands, where a substantial population lives,” says Lyon.

In the highlands, sometimes referred to as the Roof of Africa, the height of the rugged mountain summits range from about 5,000 feet to nearly 15,000 feet.

The study, published in the journal Environmental Research Letters, utilized a newly developed national temperature dataset for Ethiopia, made possible by NOAA’s Climate Program Office and Columbia University.

The dataset combines hundreds of surface station observations with climate model output that incorporate satellite data and other information.

Exceeding the minimum temperature thresholds necessary for malaria transmission does not itself point to an increase in the prevalence of malaria, say the researchers.

“While the dynamics of malaria transmission are complicated and control efforts may significantly limit the impact of these temperature changes, our study shows a clear softening of the climate barrier to transmission in the Ethiopian highlands, potentially putting more people at risk,” says Madeleine Thomson, co-author of the study and senior research scientist at the International Research Institute for Climate and Society at Columbia University in New York.

Until recently, Lyon says this type of study was not possible due to a lack of quality controlled and sufficiently high spatial resolution climate data.

“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,” he says.

Contact: Beth Staples, 207.581.3777