Malaria: How will climate change affect the spread of the vector-borne disease?

A new study demonstrates water’s vital role in the spread of malaria and what effect climate change will have on transmission in the future.

Malaria: how will climate change affect the spread of the vector-borne disease?
There may be fewer mosquito-friendly breeding sites in Africa in the future according to new research. Photo by Егор Камелев on Unsplash

Determining how water flows across the continent and what effect the real-world processes of evaporation, infiltration and river flow has helped researchers create an in-depth picture of malaria-friendly conditions in Africa.

The new study used climactic and hydrological models to show water’s role in the spread of malaria and how the hot dry conditions brought about by climate change will decrease the number of areas suitable for transmission from 2025 onwards. This could lead to more targeted interventions to control the disease in Africa, where 95% of global cases occur.

Water matters

Malaria is a climate-sensitive disease. Previous studies have focussed on rainfall totals to imply the presence of surface water suitable for breeding mosquitoes. But the new study looked at water across the African continent to create an in-depth picture of malaria-beneficial conditions.

“This will give us a more physically realistic estimate of where in Africa is going to become better or worse for malaria,” explains Dr Mark Smith, an Associate Professor in Water Research at the University of Leeds.

The findings emphasised the role of waterways like the Zambezi River in spreading the disease and revealed that the estimated population living in such areas for up to nine months of the year was four times higher than previously thought.

“And as increasingly detailed estimates of water flows become available, we can use this understanding to direct prioritisation and tailoring of malaria interventions in a more targeted and informed way,” Smith adds. “This is really useful given the scarce health resources that are often available.”

Moving water

In recent years, the decrease in malaria cases there have slowed or even reversed, partly because of stagnation in investments in global responses to malaria control. Researchers predict the hot and dry conditions fuelled by climate change will lead to an overall decrease in areas suitable for malaria transmission, but that these changes are more sensitive to greenhouse gas emissions than previously thought.

“The key advancement is that these models factor in that not all water stays where it rains, and this means breeding conditions suitable for malaria mosquitoes too can be more widespread – especially along major river floodplains in the arid, savannah regions typical of many regions in Africa,” says Professor Chris Thomas from the University of Lincoln. “What is surprising in the new modelling is the sensitivity of season length to climate change – this can have dramatic effects on the amount of disease transmitted.”

Malaria: how will climate change affect the spread of the vector-borne disease?
Four times as many people live along the Zambezi river than previously estimated. Photo by Sean Peter on Unsplash

“Our study highlights the complex way that surface water flows change the risk of malaria transmission across Africa, made possible thanks to a major research programme conducted by the global hydrological modelling community to compile and make available estimates of climate change impacts on water flows across the planet,” adds Simon Gosling, Professor of Climate Risks & Environmental Modelling at the University of Nottingham. “Although an overall reduction in future risk of malaria might sound like good news, it comes at a cost of reduced water availability and a greater risk of another significant disease, dengue.”

The researchers hope further developments in their modelling will allow for even finer details of waterbody dynamics which could help inform national malaria control strategies. “We're getting to the point soon where we use globally available data to not only say where the possible habitats are, but also which species of mosquitoes are likely to breed where, and that would allow people to really target their interventions against these insects,” Smith concludes.

News Reference

Mark W. Smith et al. Future malaria environmental suitability in Africa is sensitive to hydrology, Science