Malaria transmission areas in Africa could shrink
Published: Friday, May 10th 2024, 08:10
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As a result of climate change, malaria transmission areas in Africa could shrink more than previously assumed. A research team predicts in the journal "Science" that by the end of the century there will probably be an overall decrease in suitable areas in terms of temperature and water availability.
The malaria pathogen (Plasmodium) is transmitted by Anopheles mosquitoes, whose distribution depends, among other things, on the availability of water reservoirs as breeding grounds.
According to the World Health Organization (WHO), 249 million malaria infections were recorded worldwide in 2022, 94% of which were in Africa. Worldwide, 608,000 people died from the disease that year, 76% of whom were children under the age of five.
Water as a breeding ground
Among other things, the air temperature influences how quickly the vector mosquitoes and the plasmodia develop in the insects' bodies. Surface water - depending on the mosquito species, for example, puddles, pools or riverbanks - is an important breeding ground.
In most calculations on 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, this alone is not a good indicator of the availability of standing water.
The researchers now also included other hydrological characteristics 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 on the Nile.
Significant degree of uncertainty
According to Smith's team, the combined models suggest that the total area of Africa suitable for malaria transmission will decrease between 2025 and 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 a year would become larger - this would mainly affect regions along large rivers. As more people live in these regions, up to four times as many people could live in future year-round malaria regions according to the modeling.
However, in an independent assessment, Mario Recker from the Institute of Tropical Medicine at the University of Tübingen comments that the study contains a considerable degree of uncertainty, which the authors have not taken into account: For one thing, the underlying climate prediction models themselves contained uncertainties. "Perhaps the biggest question mark, however, is the assumption that, apart from future population forecasts, all other environmental variables that influence the risk of disease will remain constant over the forecast period of 50 to 80 years considered here," says Recker.
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 of the number of people at risk reported in the modeling projections should also be viewed with caution. "After all, the climate does play an important role in the malaria transmission cycle, 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 there is not necessarily an immediate risk in an area that is considered suitable for malaria transmission. "Malaria was endemic in large parts of Europe until the mid-20th century, but was successfully eliminated through improved infrastructure, healthcare and land management," explains Recker. However, whether or not resources should be prioritized to certain areas that could become malaria hotspots in 50 years' time is controversial, "especially given the uncertainties associated with these forecasts".
Triumph of the tiger mosquito
However, it seems certain that countries beyond Africa will also be affected in the future where malaria currently plays little or no role: forecasts predict that malaria, as well as diseases such as Zika and dengue fever, will spread further north in the future - including in Europe.
Cases of chikungunya, dengue and malaria have recently increased in southern Europe, and there have also been several Zika infections. These diseases are transmitted by species that are not native to this region, but are increasingly spreading in Europe as a result of climate change.
Malaria is notifiable in Germany, Austria and Switzerland. A malaria-carrying mosquito has recently reappeared in southern Italy after 50 years. In the first half of the 20th century, Italy fought hard against the malaria plague. Many swamp-like areas were drained in order to stop the spread of malaria. Malaria was also a problem in Switzerland until many swamps were drained.
©Keystone/SDA
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