Enter your email address below to log in or register a new account.
🦟 How climate change affects the spread of infectious diseases
For most of the December holidays, my home in Johannesburg has reeked of citronella oil in an attempt to ward off mosquitoes. Joburg is not a malaria area, so mosquitoes are just a nuisance. But imagine if that changed.
South Africa’s malaria areas are in Limpopo, KwaZulu-Natal and Mpumalanga near the borders with Zimbabwe and Mozambique. The map below from the Malaria Atlas Project showing malaria cases in 2022 in 5km x 5km blocks gives a good idea of where the malaria areas are.

South Africa aims to eradicate malaria by 2030. It appears to be making good progress as the number of reported cases have plunged from 64,622 in 2000 to 9,795 in 2023, according to Department of Health data.
But rising temperatures may make it harder to meet that target because temperature affects the growth cycle of the parasite that causes malaria (mostly Plasmodium falciparum in SA). At temperatures below 20°C it cannot complete its growth cycle in a mosquito, so malaria cannot spread. Areas higher than about 1,000m above sea level are also usually malaria free. Joburg is over 1,700m above sea level.
In many other African countries, thousands of people die every year from the disease. The Malaria Atlas Project, in a report entitled Climate Impacts on Malaria in Africa published in November 2024, predicts that thanks to climate change more people will die of malaria and notes that more investment is needed in the fight against the disease.

There’s an intricate interaction between climate change and infectious diseases, according to the scientists of the Climate Consortium who put together the Climate Change & Epidemics 2024 report released in November.
A side note: the report was edited by Tulio de Oliveira, the SA scientist who became a household name during Covid and who has been listed among the top 1% of highly cited researchers globally in 2024.
There are three main ways the interaction of climate change and disease plays out, according to the report.
Firstly, the ‘slow but relentless’ increase in temperature allows diseases such as malaria and dengue fever, which is also spread by mosquitoes, to appear in places that were previously unaffected.
Secondly, the increasing frequency of extreme weather events, such as floods.
Thirdly, changes in temperature and rainfall prompt people to migrate. If water becomes scarce and crops fail and people will be forced to move in search of food and economic opportunity.
Dengue fever
In 2024, the world’s largest epidemic of dengue fever was recorded. Although South American countries were hardest hit, dengue cases in African countries increased by 140%, from 48,800 in 2023 to over 118,000 by October 2024.
The map below shows where cases of dengue fever were reported in African countries in 2023 and 2024. Ethiopia had the misfortune of experiencing two dengue outbreaks in the past two years.

No dengue fever cases have been reported in South Africa but, says the National Institute of Communicable Diseases, the type of mosquito that carries dengue fever, Aedes aegypti, is present in certain regions, such as the KwaZulu-Natal coastline.
Floods, droughts and cholera
The increasing frequency of extreme or severe weather events, such as floods, cyclones, extreme temperatures and droughts damage infrastructure, contaminate drinking water sources and reduce access to clean water, creating an ideal environment for cholera to thrive.
Seventeen African countries reported more than 1,000 cases each of cholera in 2023 and 2024. Many of these cholera outbreaks were linked to or made worse by weather-related disasters. The map below shows those countries as well as weather-related disasters reported over the same period in the EM-DAT international disaster database.

Malawi, for example, experienced its biggest cholera outbreak ever thanks to flooding caused by two tropical cyclones in early 2022. Then in March 2023, Cyclone Freddy, hit. The cholera health emergency lasted from December 2022 until July 2024. In 2023 and 2024 alone more than 41,000 cases of cholera were recorded in Malawi by the WHO and more than 1,000 people died.
Cyclones and heavy rains also intensified a cholera outbreak in Mozambique, and epidemics in Zambia and Zimbabwe were exacerbated by both drought and floods.
South Africa’s cholera outbreak in 2023 was not weather-related, but started when an infected person travelled from Malawi to Gauteng. Similarly, an outbreak in the Comoros this year has been linked to a passenger who arrived on a boat in January.
Migration
Changing rainfall patterns such as severe drought can push people to migrate away from affected areas, as can conflict.
In the Democratic Republic of Congo conflict and floods has forced people to move to camps where conditions are crowded and access to clean water is limited. In Ethiopia, Sudan and Somalia, the internal displacement of people worsens cholera outbreaks.
In Sudan, conflict since April 2023 has caused the displacement of 10-million people. Here too floods have worsened the situation.
Poverty, malnutrition, poor sanitation, lack of access to clean drinking water and poor access to health care are exacerbated by changing climate patterns.
There is a need for infrastructure that can withstand extreme weather and ensure medical supplies during crises, states the Climate Change and Epidemics Report. Countries need to build systems to ensure communities are able to adapt to changing conditions and are less vulnerable to disease outbreaks.