Europe’s unusually warm and humid summer in 2025 contributed to 718 human cases of West Nile virus and 49 deaths in Italy alone.
From mosquitoes carrying dengue and chikungunya in Indian Ocean islands to West Nile virus now endemic in parts of Europe, climate change is redrawing the global map of infectious disease.
It is fuelling new epidemics globally, warns a new COP30 synthesis report by the Climate Amplified Diseases & Epidemics (Climade) Consortium, a coalition of leading scientific and public health organisations.
The report said rising temperatures, extreme weather, evolving pathogens and climate-driven migration are already intensifying outbreaks worldwide.
“We know from very accurate data that climate change has the potential to aggravate over 50% of pathogens,” Tulio de Oliveira, the co-lead of Climade and director of the Centre for Epidemic Response and Innovation (Ceri) at Stellenbosch University, said at the launch of the report.
“What we’re talking about is over half of disease being amplified by climate change, getting the perfect storm between climate extreme events and then infectious disease.”
The Global South contributes less than 10% of global emissions, but will bear the most significant health effects due to its proximity to biodiversity hotspots, high baseline disease burdens, and limited healthcare access.
“Addressing the intersection of climate change and infectious diseases is therefore urgent. Climate action must go hand in hand with efforts to strengthen health systems, particularly in underserved and climate-vulnerable regions,” the report urged.
Climade brings together leading scientific and public health groups, capable of responding to climate-amplified epidemics.
“Our goal is to use science and collaboration to anticipate outbreaks before they happen and to ensure that vulnerable communities are not left behind as the climate continues to change,” De Oliveira said.
Climate change strains on communities already facing food, water and health insecurity. Yet the report outlined how one of its most critical consequences often goes overlooked: its influence on infectious disease.
Research shows that climate change may intensify more than half of all known human pathogens — as evidenced by outbreaks of Oropouche virus, novel chikungunya variants, dengue, influenza, cholera and malaria, the report said.
Four main mechanisms drive these trends: rising temperatures that extend disease-vector ranges; evolving pathogens; extreme weather that creates outbreak conditions; and climate migration that increases exposure and strains fragile health systems.
Rising temperatures accelerate mosquito development, shorten virus incubation, and lengthen transmission seasons. Increased rainfall expands breeding sites, while humidity prolongs mosquito lifespans.
For instance, Aedes aegypti and Aedes albopictus were recently detected in Chandannath, Nepal, at 2 438m — the first time these vectors were found at such an altitude.
“Gradual shifts in temperature, rainfall and humidity are causing important changes in the risk of infectious disease transmission. This is particularly evident for vector-borne diseases such as arboviruses (viruses transmitted to humans by mosquitoes and ticks), whereby gradual climatic changes are stimulating outbreaks in new areas and with increased intensity.”
Chikungunya: a global comeback
Between 2024 and 2025, chikungunya, a mosquito-borne viral disease, surged globally, with more than 400 000 cases and 155 deaths across 40 countries.
Rising temperatures, shifting rainfall and expanding mosquito habitats fuelled the spread of the Ecsa (East-Central-South-African) genotype — a variant well adapted to Aedes mosquitoes — from the Indian Ocean to Europe, Asia and the Americas.
“The 2025 outbreak is a stark reminder of the impact of climate change on infectious diseases,” said Yajna Ramphal, research project manager at Ceri South Africa.
She explained that gradual warming and more frequent extreme weather accelerate the emergence of viruses such as chikungunya. First identified in Tanzania in 1952, it has evolved into multiple lineages. The 2025 resurgence began in Réunion Island, spread to Mauritius and Mayotte, and leapt to Italy, France, and China, where over 16,000 cases were recorded.
“The resurgence was driven by the Ecsa genotype, intrinsically linked to climate change,” Ramphal said. “It has extended the geographical range and seasonal activity of Aedes mosquitoes, the virus’s primary vector.
“The resurgence demonstrates the capacity and adaptation of the virus to changing climatic realities, rewriting the geography of arbovirus transmission.”
Ramphal called for greater investment in surveillance, integrating weather, vector and genomic data to predict and stop epidemics, alongside sustainable funding, robust diagnostics and equitable vaccine access.
West Nile virus: Europe’s new normal
Europe’s unusually warm and humid summer in 2025 contributed to 718 human cases of West Nile virus and 49 deaths in Italy alone.
Climate affects mosquitoes and the diseases that they carry in multiple ways, said Monika Moir of Ceri South Africa.
“Higher temperatures can increase mosquito activity rates, which affect how often they are biting humans. Increased rainfall can facilitate their breeding, and higher humidity can prolong their lifespans.”
These factors can then increase mosquito population sizes, lengthening and intensifying disease transmission seasons. Climate change can also affect mosquitoes and their diseases by allowing them to spread into new regions.
Previously unaffected regions are now suffering large outbreaks of West Nile virus, she said, adding: “For example, in Europe, they are experiencing widespread West Nile virus transmission, with cases recorded from 14 countries in 2025 alone.”
West Nile virus is an example of a climate-sensitive pathogen transmitted by mosquitoes and is now considered the most widespread arbovirus worldwide. Climate change may intensify West Nile virus transmission in Africa, particularly in regions with limited surveillance and control.
“Considering how interconnected our world is, this virus poses a major global health threat,” said Moir, adding that although West Nile virus originated in Africa and is endemic to the continent, it remains poorly characterised.
She called for governments to strengthen surveillance through a One Health approach that integrates animal, human and environmental data.
“We must adopt climate-informed surveillance systems and vector control programmes, backed by sustainable funding and regional collaboration.”
Africa at the epicentre
Africa is the world’s most climate-vulnerable region, with temperatures rising faster than the global average and projected warming of up to 3°C by mid-century. More than 60% of Africans rely on rain-fed farming, so even minor climate shocks can trigger severe food and livelihood crises.
By 2050, climate change could drive 1.2 million cross-border displacements — roughly 10% of total migration — with the Horn of Africa, the Sahel, and southern Africa most affected, the report said.
Southern Africa is projected to see the highest inflows, including South Africa, Zimbabwe, Mozambique and Botswana, while Namibia, Zambia and Malawi may experience significant outflows.
Climate-driven migration amplifies infectious disease risks, as people move into regions where malaria, dengue, and chikungunya are endemic.
Overcrowded settlements, poor sanitation, and shifting rainfall extend mosquito breeding seasons, allowing illnesses to spread. Fragile health systems are overwhelmed, reducing care, vaccination and surveillance capacity, the report said.
Building a climate-informed global response
The authors urge governments, academic institutions, scientists, public health officials, private industries, and health organisations to address the urgent, interconnected challenges of climate-amplified diseases using their expertise and resources.
Interventions include strengthening surveillance through genomic and epidemiological monitoring within a One Health framework to enable early detection and rapid response.
Vulnerable communities must be prioritised, ensuring equity and inclusion are central to adaptation strategies. Long-term financing is needed for research, data sharing, and capacity-building to anticipate and mitigate health impacts before crises unfold.
Outbreaks should be reported promptly, and climate resilience promoted through innovation, cross-sector partnerships, and integrated solutions that link climate adaptation and healthcare delivery.
“Climate risk isn’t tomorrow’s story — it’s today’s patient list,” said Sikhulile Moyo of the Botswana Harvard Health Partnership.
“Fund the science, finance the response and count the lives saved.”