Climate change is, to put it simply, a real mess. Not only is it affecting our food sources and crime, but a new study finds that it may soon affect illness in the highlands of South America and Africa. That’s because as it gets warmer, malaria carrying mosquitos are exploring new heights, and infecting people who were once at an altitude too high for them to reach.

Malaria is a disease caused by the parasite Plasmodium, which infects mosquitos living in mostly warm climates that subsequently bite humans, passing on the infection. In humans, the parasite multiplies in the liver, and spreads throughout the body from there, infecting red blood cells, according to the World Health Organization (WHO). After about 10 to 15 days, the infection causes fever, headache, and vomiting, but usually gets worse, becoming life-threatening when it disrupts the blood supply to vital organs.

Currently, the WHO estimates that 3.4 billion people worldwide are at risk of malaria infection. In 2012, there were an estimated 207 million cases of the infection with about 627,000 deaths among them. Since 2000, rates of infection and death have gone down by 29 percent and 45 percent, respectively, but climate change may cause them to jump again, as people who live at higher, colder altitudes experience unseasonably warmer temperatures.  

Researchers from the University of Michigan have seen trends toward this reality in the highlands of Ethiopia and Colombia, both of which kept detailed records of malaria infections and temperatures between the 1990s and 2005. Looking at these records, they found that malaria did indeed shift toward the upper regions during warmer years, while shifting to lower altitudes during colder years.

“The impact in terms of increasing the risk of exposure to disease is very large,” Professor Mercedes Pascual, from the university, told the BBC. This risk compounds as malaria infections go further up into the mountains, where “populations lack protective immunity,” putting them at a higher risk of death from the disease, co-author Menno Bouma, of the London School of Hygiene & Tropical Medicine, said in a press release.

The findings hold grave implications for many citizens of higher, warm-climate areas. In the Debre Zeit region of Ethiopia, 37 million people (about 43 percent of the country’s population) live at an elevation between 5,280 and 7,920 feet. A previous study found that the temperature would only have to increase by one degree Celsius to cause an additional three million malaria cases annually in the under-15 population of Ethiopia.

“This is indisputable evidence of climate effect,” Pascual said in the statement. “The main implication is that with warmer temperatures, we expect to see a higher number of people exposed to the risk of malaria in tropical highland areas like these. Our findings underscore the size of the problem and emphasize the need for sustained intervention efforts in these regions, especially in Africa.”

Source: Siraj A, Santos-Vega M, Bouma m, et al. Altitudinal Changes in Malaria Incidence in Highlands of Ethiopia and Colombia. Science. 2014.