When Mosquitoes Move North: Climate-Sensitive Diseases Expand
Rising temperatures aren’t just making summers hotter—they’re enabling tropical diseases to expand into regions once too cold to support transmission. Dr. Madeleine Thomson, who directed the WHO Collaborating Centre on Early Warning Systems for Climate Sensitive Diseases at Columbia University, has spent over 25 years studying this transformation.
“We know that virtually all vector-borne diseases have a climate dimension,” she explains. “Temperature drives the rate at which vectors and pathogens develop, while rainfall often supports the creation of sites for the vectors to breed.”
Mosquitoes carrying dengue fever now threaten France and other European countries because of warmer summers. When Paris prepared for the 2024 Olympics, dengue was among organizers’ top health concerns—a disease traditionally considered tropical, not European.
Highland areas of eastern Africa and Latin America that were previously malaria-free are becoming vulnerable as temperatures rise. Lyme disease, spread by ticks, is pushing northward into Canada and even Arctic regions once too cold for ticks to survive.
In Pakistan, increasingly intense monsoons linked to climate change trigger devastating floods. When waters recede, stagnant pools create ideal mosquito breeding grounds. Malaria cases surged from 500,000 in 2021 to 1.3 million by 2024, with numbers continuing to climb.
“The recent expansion of mosquitoes is very much associated with globalization—things like the movement of shipping containers around the world, air travel, population movement, forest clearing and urbanization,” Thomson notes. “We have to expect more of this type of emergence: new diseases that were historically isolated which can spread very rapidly.”
Temperature changes interact with human activity—trade, travel, deforestation—creating new disease pathways that once-isolated pathogens can exploit.
