As a result of climate change, the areas where malaria is transmitted in Africa could shrink more than previously thought. A research team in the journal "Science" predicts that by the end of the century there will probably be a reduction in the number of areas suitable for malaria in terms of temperature and water availability. The malaria pathogen (Plasmodium) is transmitted by Anopheles mosquitoes, the spread of which depends, among other things, on whether water reservoirs are available as breeding grounds.

According to the World Health Organization (WHO), 249 million malaria infections were recorded worldwide in 2022, 94 percent of which were in Africa. Worldwide, 608,000 people died of the disease that year, 76 percent of whom were children under five.

Water as a breeding ground

The air temperature influences, among other things, how quickly the vector mosquitoes and the plasmodia develop in the insects' bodies. Surface water - depending on the mosquito species, for example puddles, ponds or river banks - is an important factor as a breeding ground.

In most calculations of the effects of climate change on malaria, only the predicted amount of precipitation is taken into account for water, explains the team led by Mark Smith from the University of Leeds. However, it alone is not a good indicator of the availability of standing water.

The researchers now also included other hydrological features such as evaporation and water runoff. This is important, among other things, because it directly depicts river systems and floodplains, where population centers are often located, such as the Nile.

Significant level of uncertainty

According to Smith's team, the combined models suggest that the total area of ​​areas suitable for malaria transmission in Africa will decrease after 2025 to 2100, for example in large parts of West Africa.

At the same time, however, the areas in which the malaria pathogens can be transmitted for at least nine months per year would become larger - this particularly affects regions along large rivers. Since more people lived in these areas, according to the models, up to four times more people could live in regions with malaria all year round in the future.

In an independent assessment, Mario Recker from the Institute for Tropical Medicine at the University of Tübingen comments that the study contains a considerable degree of uncertainty that the authors did not take into account: On the one hand, the underlying climate prediction models themselves contained uncertainties.

"Perhaps the biggest question mark, however, is the assumption that, apart from future population projections, all other environmental variables that influence disease risk will remain constant over the forecast period of 50 to 80 years considered here," said Recker.

Expert remains cautious

The expert also warns against interpreting the results of the study in such a way that climate change will lead to a decline in malaria - the quadrupling in the number of people at risk reported in the modeling projections should also be viewed with caution. "Ultimately, climate plays an important role in the transmission cycle of malaria, but intervention measures and future developments will probably have a much greater impact on this disease than climate change," emphasizes Recker.

It is important to remember that an area considered suitable for malaria transmission does not necessarily pose an immediate risk. "Malaria was endemic in large parts of Europe until the mid-20th century, but was successfully eliminated through improved infrastructure, health care and land management," explains Recker.

However, whether or not resources should be prioritized toward specific areas that could become malaria hotspots in 50 years is controversial, "particularly given the uncertainties associated with these projections."

Triumph of the tiger mosquito

What seems certain, however, is that beyond Africa, countries in which malaria currently plays little or no role are likely to be affected in the future: Forecasts describe that malaria, but also diseases such as Zika and dengue fever, will spread further north in the future - also in Europe.

Chikungunya, dengue and malaria cases have recently become increasingly common in southern Europe, and Zika infections have also occurred several times. These diseases are transmitted by species that are not native here, but are spreading increasingly in Europe and Germany as a result of climate change.

Malaria has been considered eradicated in Germany since the mid-1950s, partly due to the use of the insecticide DDT. Until the 19th century, however, there were regular malaria epidemics with many deaths in large parts of Europe.