The worldwide incidence of malaria could rise as temperatures warm due to climate change, according to a recent study Reuters reported.

Ecologists from the University of Michigan and their colleagues are reporting that the mosquito-borne disease that infects more than 300 million people each year creeps to higher elevations during warmer years and back down to lower altitudes when temperatures are cool.  This trend could increase the number of people sickened by the disease, Agence France Presse reported.

Their  study, which is based on an analysis of records from highland regions of Ethiopia and Colombia, suggests that future climate warming will result in a significant increase in malaria cases in densely populated regions of Africa and South America, unless disease monitoring and control efforts are boosted and sustained.

"We saw an upward expansion of malaria cases to higher altitudes in warmer years, which is a clear signal of a response by highland malaria to changes in climate," said University of Michigan theoretical ecologist Mercedes Pascual, said in a statement.

For the study, Pascual and her colleagues looked for evidence of a changing spatial distribution of malaria with varying temperature in the highlands of Ethiopia and Colombia. They examined malaria case records from the Antioquia region of western Colombia from 1990 to 2005 and from the Debre Zeit area of central Ethiopia from 1993 to 2005.

They focused solely on the altitudinal response to year-to-year temperature changes and were able to exclude other variables that can influence malaria case numbers, such as mosquito-control programs, resistance to anti-malarial drugs and fluctuations in rainfall amounts.

Pascual added that as temperatures warm, a higher number of people in tropical highland areas will be exposed to the disease.

People who live in these areas have no protective immunity; they will be particularly vulnerable to more severe and fatal cases of infection, Menno Bouma, honorary senior clinical lecturer at the London School of Hygiene & Tropical Medicine, said in a statement.

In a previous study, the researchers estimated that a 1 degree Celsius temperature increase could result in an additional 3 million malaria cases annually in Ethiopia in the under-15 population, unless control efforts are strengthened, according to a press release.