14 February 2014

Africa: Rise in Malaria Forecast for Tropical Highlands

Santiago — More people may contract malaria in the tropical highlands of Africa, Asia and South America as global warming makes the climate in these areas more suitable for the disease's transmission, according to a study.

While the study focuses on the effects of global warming, it notes that further studies will be needed to account for other factors that may influence the disease's spread, including economic development, changes in human population patterns and adaptations in the mosquitoes that transmit malaria.

The authors of the paper, published this month in Proceedings of the National Academy of Sciences (3 February), used five existing malaria impact models to make predictions for the 2030s, 2050s and 2080s.

The malaria models were run under four different carbon dioxide emissions scenarios developed by the Intergovernmental Panel on Climate Change. The researchers examined how easily disease would be transmitted and how many people would be at risk under the different scenarios.

They found that each of the five models predicted an extended the disease transmission season in the highland regions of eastern Africa, South Africa, central Angola, the plateau of Madagascar, central America, southern Brazil and the border area between India and Nepal.

Cyril Caminade, the lead author of the study and an epidemiologist at the University of Liverpool, United Kingdom, says that individual models may overlook important considerations, but because all five models predict malaria increases in the same areas, he is confident this result is reliable.

The study only modelled the Plasmodium falciparum parasite. This parasite causes the most dangerous form of malaria, accounting for 80 per cent of all malaria infections and 95 per cent of deaths. It is most prevalent in Sub-Saharan Africa.

Because of this, "one would expect more severe effects over the African continent, where the [P. falciparum] malaria burden is the largest", says Caminade. There is further danger in Africa because malaria incidence has already risen in highland areas over the past 50 years and large population growth is predicted, he says.

Caminade says the study also shows a longer malaria season in areas of Asia: across Bangladesh, northern Myanmar and the border between Myanmar and China. But he adds that the less-virulent malaria parasite P. vivax, which the study did not account for, is present in these regions.

In other areas, including tropical regions such as western Africa, Malaysia, South America and the coasts of India, the each model forecast a fall in malaria.

Simon Hales, an epidemiologist at the University of Otago, New Zealand, tells SciDev.Net that the "increase in the length of the malaria transmission season by P. falciparum in the tropical highland regions of Africa, South America and Asia is a very robust finding, given the consistency of results across the models".

Caminade also notes that studies modelling malaria risk are starting to incorporate other important drivers of disease transmission rates, such as changes in land use, urbanisation, migration, economic growth and measures to control diseases.

For example, he adds, the European Union-funded Healthy Futures project to map future risk in East Africa from malaria and two other vector-borne diseases include some of these considerations.

Link to full paper in PNAS


Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1302089111 (2014)

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