International Study Reveals New Malaria Transmission Patterns in Africa

A Global Professor at the University of Lincoln, UK, has contributed to a new international study which reveals how future climate change could affect malaria transmission in Africa over the next century.

For more than two decades, scientists have suggested that climate change may alter the distribution and length of malaria transmission seasons due to new patterns of temperature and rainfall.

The burden of this disease falls primarily on Africa. In 2018, out of an estimated 228 million cases of malaria worldwide, 93% were in the African continent.

Detailed mapping of malaria transmission is vital for the distribution of public health resources and targeted control measures.

In the past, rainfall and temperature observations have been used in malaria climatic suitability models to estimate the distribution and duration of annual transmission, including future projections. But factors affecting how rainfall results in water for mosquito breeding are highly complex, for example how it is absorbed into soil and vegetation, as well as rates of runoff and evaporation.

Now a new study by the Universities of Lincoln and Leeds in the UK, and published in Nature Communications, has for the first time combined a malaria climatic suitability model with a continental-scale hydrological model that represents real-world processes of evaporation, infiltration and flow through rivers.

Professor Chris Thomas from the Lincoln Centre for Water and Planetary Health co-authored the study alongside Dr Mark Smith from the School of Geography at the University of Leeds.

While the findings show only very minor future changes in the total area suitable for malaria transmission, the geographical location of many of those areas shifts substantially. This process-focused approach gives a more in-depth picture of malaria-friendly conditions across Africa.

When run using future climate scenarios up to the end of this century, a different pattern of future changes in malaria suitability emerges compared to previous estimates. When a hydrological model is used, aridity-driven decreases in suitability are no longer observed across southern Africa, particularly Botswana and Mozambique.

Conversely, projected decreases in malaria suitable areas across West Africa are more pronounced. The largest difference is in South Sudan, where the study estimates substantial decreases in malaria suitability in the future.

The study highlights river corridors as year-round hot spots of malaria transmission. While flowing water in large rivers is not a suitable habitat for malaria-carrying mosquitoes, nearby smaller water bodies, such as bankside ponds and floodplains can make for ideal larvae breeding grounds, as do associated irrigation schemes.

The Niger and Senegal rivers in Mali and Senegal, and the Webi Juba and Webi Shabeelie rivers in Somalia, are all identified in the study as suitable for malaria transmission despite currently extending beyond the geographical ranges hitherto predicted to be climatically suitable.

This is especially important since human populations tend to concentrate close to rivers.

Lead author Dr Mark Smith, said: “If we are to project the impact of climate change on the geography of malaria transmission, we need to develop more sophisticated ways of representing that envelope of malaria suitability both today and in the future.

“Our approach aims to lay out the environmental risks of malaria more clearly, so that projections of climate change impacts can help inform public health interventions and support vulnerable communities.”

Professor Chris Thomas said: “The shrinking map of malaria in Africa over that last 20 years is primarily due to huge public health efforts underway to tackle this disease, not climate change. “But malaria elimination is made much more difficult where the climate is highly suitable for transmission, so it is key to know where these areas are now and are projected to be in the future.

“In this study we show that linking physical geographic processes to the biology helps us get to grips with some of that complexity. The exciting challenge now is to develop this approach at local scales.”