Cyril Caminade is a guest lecturer during a week of training dedicated to the National Malaria Control Programs (NMCPs) of Africa, organized in Rwanda by L’Initiative. The World Climate Day offers the opportunity to discuss the links between climate change and malaria, particularly potential drivers of the disease’s resurgence.
Cyril Caminade
Researcher specialized in the impact of climate on the evolution of vector-borne infectious diseases at the International Centre for Theoretical Physics (Trieste, Italy), and an honorary researcher at the University of Liverpool.
How does a climatologist come to study the evolution of vector-borne diseases, particularly malaria?
Like many diseases, especially infectious ones, malaria is sensitive to climate. Epidemic risk varies based on temperature and ambient humidity. Malaria is a vector-borne disease, meaning it is transmitted by an arthropod, usually an insect, which does not regulate its internal temperature. In malaria’s case, the vector is an Anopheles mosquito infected with a parasite called Plasmodium. When the mosquito bites, it transmits the Plasmodium to humans, who fall ill, even though the mosquito itself is unaffected.
Ambient temperature influences the mosquito’s life cycle: it accelerates its reproduction, affects larval development in water, and influences the insect’s aerial development. Female mosquitoes need human blood to reproduce and lay eggs. If we compare a mosquito to a flying syringe, the time it takes for the blood to become infectious inside this syringe depends heavily on the external temperature. Below 18-20°C, the parasite’s reproduction (sporogony) doesn’t occur in the mosquito, meaning it won’t transmit malaria.
Seasonality is also a crucial factor since malaria follows precipitation patterns. Anopheles larvae develop in stagnant water, such as temporary pools and puddles. Warm, humid climates create optimal conditions for mosquitoes—and the parasites they carry—to reproduce more rapidly and in greater numbers. In Senegal, for example, most malaria cases are reported between September and October, just after the rainy season (July to September). The same trend is observed across much of the Sahel region in West Africa, including southern Mali, Niger, Guinea, and Burkina Faso. In contrast, near the equator in East Africa (e.g., Tanzania, Kenya, Ethiopia), there are two rainy seasons and, consequently, two malaria peaks.
When temperatures are too high and conditions too dry (Saharan zones) or too low (high altitudes), mosquitoes die. This is why, until recently, there was little or no malaria transmission in high-altitude regions of Ethiopia, Rwanda, Kenya, or Madagascar. However, rising temperatures have introduced mosquitoes into these areas, meaning malaria could develop and affect populations historically unexposed to the disease. Studying climate helps, at least partially, to predict outbreaks of vector-borne diseases. That’s why a climatologist may find themselves working on malaria.
What are the potential consequences of climate change on malaria epidemics?
Due to human activity and greenhouse gas emissions, the climate is changing faster than ever before. Global temperatures are rising, with faster warming observed at higher latitudes. These changes in temperature and humidity (air hygrometry) directly affect the mechanisms governing vector-borne diseases like malaria, particularly through adaptation phenomena.
Mosquitoes adapt to new climatic conditions. While Anopheles mosquitoes that transmit Plasmodium previously bit primarily at night, they now tend to bite at dawn or dusk—times when using a bed net is more challenging. Another ongoing change involves urban areas. Historically less affected by malaria than rural areas (due to fewer ponds and puddles where mosquitoes lay eggs), cities might become high-transmission zones. This risk arises from the arrival of a new Anopheles species from India (Anopheles stephensi), which can reproduce in urban and high-altitude environments. Parasites also adapt. Plasmodium falciparum, the most widespread malaria parasite in Africa, has gradually replaced other Plasmodium species, such as vivax, ovale, or malariae, which were predominant in temperate regions until the 1970s.
Additionally, extreme weather events like heatwaves, cyclones, and floods, which are becoming more intense and frequent due to climate change, increase populations’ vulnerability to vector-borne diseases. These events damage infrastructure and healthcare systems (disrupting care, making travel difficult, and increasing precarious living conditions), destroy crops, exacerbate malnutrition, and lead to poverty, displacement, and school dropouts—all factors that heighten malaria risk.
Can we anticipate the consequences of climate change to better organize health responses?
Climatologists, including those from the IPCC¹, have developed various climate scenarios ranging from optimistic to pessimistic. Current climate trends suggest a trajectory closer to the pessimistic scenarios. These scenarios inform models predicting malaria development, but the disease’s epidemiology is multifactorial, influenced by numerous dynamic factors beyond climate.
While climate plays a significant role in malaria epidemiology—following general rules like “malaria aligns with precipitation within a viable temperature range”—exceptions exist. For instance, dry-season malaria cases have recently been reported in some Sahelian countries, a phenomenon not yet fully explained. It could be linked to population movements and the importation of other Plasmodium types. Rainfall has recently increased in West Africa, leading to favorable monsoon seasons, but there remains uncertainty about future trends based on climate models. Simultaneously, rising temperatures, particularly in arid areas like the Sahel, complicate forecasts.
Human factors also significantly influence malaria’s trajectory, including poverty and malnutrition, both exacerbated by climate change. Urbanization, conflicts, population displacement, water management practices (e.g., dams creating stagnant water), and insecticide or treatment resistance are key contributors. This complexity underscores the challenges of predicting malaria’s future.
Researchers combine variables to simulate past and recent malaria transmission dynamics and project these findings into the future. In a much hotter future, malaria risk may increase in high-altitude zones, where populations are particularly vulnerable due to their lack of immunity. Epidemics in such areas could rapidly affect entire populations, potentially causing severe cases. In lowland areas from Senegal to Ethiopia, simulated risk decreases because extreme heat kills mosquitoes. However, this offers only partial relief since local populations will face unlivable temperatures.
We do have tools to combat malaria, such as medications and vaccines. However, current vaccines offer only partial protection and require multiple doses (e.g., four injections for optimal protection). Organizing successive vaccination campaigns in these regions poses significant challenges, such as the distance to healthcare centers, parental resistance to multiple injections, and doubts about vaccine efficacy when vaccinated individuals still fall ill. Additionally, resistance to antimalarial drugs like chloroquine and, more recently, artemisinin is increasing. Mosquitoes are also adapting to insecticides and becoming more resistant.
Understanding the myriad factors influencing malaria epidemics—such as climate change and its consequences—is essential for mitigating their future impacts.
- The Intergovernmental panel on climate change (IPCC) has been set up by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988. Its job is to advance scientific knowledge about climate change caused by human activities.
