Shifting Landscape: Climate Change’s Impact on Malaria

How is climate change affecting mosquitoes that transmit malaria? The answer is not as simple as you might think. 

Climate change is impacting all of our lives and prompting new questions about what the future holds. For those on the frontlines of malaria – researchers, mothers and children in endemic areas, and health policymakers – the stakes could not be higher. They are faced with navigating a future in which the distribution of malaria could shift in unpredictable ways, complicating efforts to control the spread of mosquitoes, the parasite, and the disease. 

Recent research, while still not definitive, provides a clearer picture, highlighting the complexity and regional variability of the impact of climate change on malaria and its vector.

The expanding range of African Anopheles mosquitoes

Using historical data from 1898 to 2016, researchers have been able to confirm that the geographic range of the malaria vector – Anopheles mosquito – has been expanding over the twentieth century. These mosquitoes have gained ground both in terms of latitude and elevation, particularly in highland and southern Africa, where areas once too cold for mosquitoes to thrive have now become more suitable.

Though the above findings align with the expectations of climate change impacts, there is still a need for further research that explores direct causality of climate change on the expansion of these malaria vectors.

Temperature’s myriad impact on malaria

Temperature has a complex and non-linear relationship with malaria transmission. Modelling predicts that malaria transmission is optimal at 25º C. Higher temperatures could in fact decrease transmission rates, offering some hope down the line for malaria-endemic regions in sub-Saharan Africa. However, other parts of the world are warming too, including places that were previously too cold for mosquitoes, presenting new opportunities for malaria vectors to thrive in new habitats.

In areas where malaria is already prevalent, warmer temperatures accelerate the growth cycle of the malaria parasite. Higher temperatures shorten the extrinsic incubation period, which is the time it takes for a mosquito to become infectious after feeding on infected blood, amplifying the spread of malaria. Moreover, high temperatures could also influence the efficacy of insecticides widely used in malaria control strategies, as seen in this laboratory study. 

While the link between temperature and malaria is still being investigated, we are already observing numerous other impacts of climate change on this deadly disease.

The promise of unpredictable extreme weather events

Until now, many malaria interventions have relied on predictable dry and rainy seasons, enabling timely deployment of prevention strategies like seasonal malaria chemoprevention and indoor residual spraying. However, climate change is lengthening malaria transmission seasons and creating unpredictable malaria surges, challenging the health system’s abilities to prevent and control the disease.

Extreme weather events like excessive rainfall, floods and cyclones claim lives, destroy homes and leave behind ideal breeding grounds for mosquitoes. Sometimes they wash away recently sprayed insecticides, other times they damage health facilities including essential supplies like diagnostics and antimalarials.

In 2022, Pakistan saw a five-fold increase in malaria cases after floods caused by melting glaciers in the Himalayas and rising sea levels in the Indian Ocean. 

For the BOHEMIA project, the largest ivermectin for malaria trial in Africa, to date, extreme weather events emerged as the biggest challenge. In Mozambique, Cyclone Gombe severely disrupted the trial by displacing participants from their homes, destroying critical road infrastructure and leaving behind a spike in cholera and malaria cases in its wake. Meanwhile in Kenya, heavy rains also led to flooding and a power outage that impacted data collection. 

Not just humans, other endangered species are at risk

In Hawaii this year, millions of male mosquitoes with a naturally occurring bacteria that stops the eggs of wild females that they mate with from hatching, were released to save endangered honeycreeper birds. The rare birds are being decimated by avian malaria and the only remaining birds live at 1,200-1,500 metres altitudes, which is still too cold for the mosquitoes. But with climate change, there is a growing fear that the mosquitoes will soon be able to survive and thrive in higher elevations of the island. 

Protecting the gains against malaria

Decades of global progress against malaria are now at risk due to the growing impact of climate change. Malaria programs are now faced with the inevitable task of adapting existing malaria prevention and control tools to these new climate realities. Initiatives like the FORECAST project in Uganda are pioneering early warning systems to better prepare for and manage outbreaks of mosquito-borne diseases. 

Securing sustainable funding for research and innovation is also essential as we confront a convergence of biological threats – drug and insecticide resistance, genetic mutations that undermine diagnostics, and the spread of invasive malaria vector species into new regions. Without continued investment, local leadership, and global collaboration, these challenges could undermine decades of progress, making the fight against malaria more difficult and urgent than ever before.

While climate adaptation is critical, the global health and malaria community also bears a significant responsibility to mitigate climate change. A report on healthcare’s climate footprint reveals that if the global health sector was a country, it would be the fifth-largest emitter of greenhouse gases in the world. The sector’s energy-intensive manufacturing, plastic packaging, and cold chain supply systems contribute substantially to these emissions. This reality demands that global health actors critically examine their carbon footprint and commit to climate-smart strategies and decarbonization, ensuring that the fight against malaria does not come at the cost of our planet’s future.

Lastly, while the potential decrease in malaria incidence under the “middle-of-the-road” climate scenario outlined in a study commissioned by the World Health Organization might seem like a silver lining, we must not forget that a world too hot for mosquitoes is no better for humans. Such a scenario would bring major challenges, including drought, rising sea levels, and food insecurity, all of which will disproportionately impact the most vulnerable populations.

The fight against malaria must therefore be strengthened and sustained, while being part of a broader multi-sectoral response to climate and health.