Study warns climate shifts could widen malaria risk across Africa

A study in Global Change Biology reports that future warming could create more favourable conditions for mosquitoes across Africa, potentially exposing millions more people to dangerous malaria bites.

Mosquitoes now contribute to a variety of diseases, including malaria, dengue, chikungunya, and others, that have severe adverse effects on human health. As a result, an additional 200 million to as many as one billion people could be placed at increased risk.

The study examined how climate change could affect malaria-carrying mosquitoes in sub-Saharan Africa, focusing on six of the main vector species. The researchers combined an extensive dataset of mosquito observations with models that project changes in habitat suitability under future climate and land-use scenarios.

Their primary goal was to understand how suitable different regions of Africa would become for each mosquito species in the coming decades and to assess the potential impact on human exposure to malaria.

The study found that three key species, Anopheles gambiae, Anopheles coluzzii, and Anopheles nili, are expected to experience a substantial expansion in their suitable habitats across the continent as climate change progresses.

By integrating these habitat projections with population data, the researchers estimated that roughly 200 million more people could be living in areas highly suitable for these vectors by the end of the century under conservative assumptions of population growth and climate change.

In more extreme scenarios with higher population growth, this number could rise dramatically, potentially exposing up to a billion people to new high-risk zones for malaria.

Importantly, the study highlighted that climate change will not affect all mosquito species in the same way. Different species respond uniquely to changes in temperature, precipitation, and land use, meaning that malaria risk is likely to shift geographically. Some regions may see a significant increase in mosquito populations, while others could experience reduced risk.

The findings have serious implications for public health in Africa. Areas that were previously considered low-risk or malaria-free may become suitable for mosquito vectors, potentially reversing progress in malaria control. A larger portion of the population may face increased risk, putting pressure on health systems and public health programs.

Malaria remains a leading cause of illness and death in sub-Saharan Africa, particularly among children. It is caused by Plasmodium parasites, which are transmitted to humans through the bite of infected female Anopheles mosquitoes.

The disease primarily affects red blood cells and the liver, leading to symptoms such as high fever, chills, headache, fatigue, nausea, and body aches. In severe cases, malaria can cause anaemia, organ failure, seizures, or death, particularly in young children, pregnant women, and people with weakened immune systems.

The three primary malaria vector mosquitoes discussed in the study, Anopheles gambiae, Anopheles coluzzii, and Anopheles nili, are all significant transmitters of malaria, particularly caused by Plasmodium falciparum, which is the deadliest form of the disease, and to a lesser extent, Plasmodium vivax.

Each species has specific environmental and ecological preferences that influence its distribution, abundance, and the associated risk to humans.

Anopheles gambiae

Anopheles gambiae thrives in warm, humid environments with abundant standing water, such as puddles, swamps, and rice fields. This species is highly anthropophilic, meaning it prefers feeding on humans, which increases the likelihood of malaria transmission in populated areas.

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Its presence is particularly strong in rural and peri-urban regions where sanitation and drainage are poor, and mosquito control interventions like bed nets and indoor residual spraying are limited.

Anopheles coluzzii

Anopheles coluzzii, closely related to Anopheles gambiae, shares many of the same environmental requirements, flourishing in humid tropical climates with stagnant water sources.

This species is highly adaptable and is often found in urban or semi-urban areas, particularly around irrigated agricultural land. Its ability to thrive in human-modified environments makes it an important vector in regions experiencing urbanisation and agricultural development.

Climate change is expected to expand its range, further increasing the human population at risk.

Anopheles nili

Anopheles nili prefers breeding in slow-flowing rivers, streams, and shaded pools, typically found in forested or semi-forested areas. Human activities such as deforestation and encroachment into forested zones can lead to population increases for this species.

While less studied than Anopheles gambiae and Anopheles coluzzii, Anopheles nili is a recognised vector of Plasmodium falciparum malaria and contributes to localised transmission in parts of West and Central Africa.

While all three mosquito species are primarily known for transmitting malaria, research indicates that these mosquitoes can also play a role in transmitting other pathogens, though less efficiently or less commonly than malaria.

Here’s a detailed overview:

Lymphatic Filariasis

Some Anopheles species can transmit Wuchereria bancrofti, the parasite that causes lymphatic filariasis, also known as elephantiasis. This disease leads to severe swelling of the limbs and genitals and can result in lifelong disability. While An. gambiae is capable of transmitting this parasite, the transmission efficiency varies by region and mosquito population.

O’nyong’nyong virus

Anopheles mosquitoes, particularly Anopheles gambiae and Anopheles funestus, have been linked to the transmission of the O’nyong’nyong virus, a mosquito-borne virus in the same family as Chikungunya. Infection can cause fever, rash, joint pain, and malaise. Large outbreaks have historically occurred in East and Central Africa.

Potential for other arboviruses

Although Anopheles mosquitoes are less efficient vectors for viruses compared to Aedes mosquitoes, some studies suggest they can carry arboviruses under certain conditions, including Rift Valley Fever virus or Zika virus in experimental settings. However, these transmissions are rare and typically not the primary route of human infection.