Paris, Vienna, Zagreb and other European cities will be at more risk of dengue, Zika and chikungunya outbreaks as climate change expands mosquito range

In the past century, the Asian tiger mosquito (Aedes albopictus) has spread far beyond its native range of southeast Asian forests, establishing itself in temperate climates and human habitats in every continent bar Antarctica. Its spread has been facilitated by numerous adaptations – from laying eggs in man-made water reservoirs to producing eggs that are more resilient to drought and cold. Global trade has also contributed to its transport around the world – for example mosquitos stow away in items like potted plants and used tyres. 

As well as bringing the nuisance of bites, the spread of this mosquito is of particular concern due to the public health risk they pose: the Asian tiger mosquito can carry dengue, chikungunya, and Zika (arboviruses) – all serious diseases. The species prefers, and is a more efficient disease-spreader, in warm climates – therefore the health risk is likely to increase as climate change progresses. 

This brings potentially significant impacts for European cities. In fact, 2024 saw the most dengue cases ever recorded globally, and the worst dengue outbreak ever reported in western Europe. In 2022, the European Environment Agency issued a report on the heat- and infectious disease-related threats to health and wellbeing as a result of climate change, projecting that Europe will see a further spread of climate-sensitive infectious disease and a higher disease burden in coming years. As well as climate change mitigation efforts, we need better adaptation to improve health resilience, states the report – addressed in the EU Adaptation Strategy adopted in 2021. 

This strategy saw the establishment of the European Climate and Health Observatory, which aims to track, analyse, and prevent climate-related impacts on human health. The EU4Health programme (2021-27) also targets resilience in national health systems, which were shown to be fragile to cross-border health threats in the aftermath of the COVID-19 pandemic. Policymakers are keen to stress that heightened risks of vector-borne disease do not justify preventative use of pesticides, however, which carry their own health risks.

To inform our understanding of the growing risk posed by Asian tiger mosquitoes, researchers have modelled the impact of recent climate change (since 2006) on the species’ spread and risk of transmission of dengue in western Europe. The researchers compared their results to entomological and epidemiological observations from the last 20 years, also drilling down to explore a subset of municipalities in France in more detail. Finally, they analyse how changes in temperature, rainfall, and human population density may affect dengue transmission risk.

The study’s projections of mosquito distribution and dengue transmission risk match the observations for western Europe well. By the 2010s, large proportions of southern Europe were already suitable for the establishment of an Asian tiger mosquito population, with the exception of mountainous areas. By the 2020s, much of western Europe provided suitable conditions. 

Some cities and regions have been climatically suitable for hosting the species since 2010, such as lowlands in southern Europe. Others have become suitable more recently, for example the cities of London, Zagreb, Frankfurt, Paris, and Vienna. The areas currently suitable for the establishment of the Asian tiger mosquito in Europe include both large, continuous regions (the Spanish plateau, French Atlantic coast), and isolated urban centres, according to the model. Interestingly, it is middle-sized cities that appear most at risk of dengue epidemics – a finding supported by recent outbreak reports across Europe. For instance, there was a chikungunya outbreak in Ravenna (population 150,000) in 2007 and a dengue outbreak in smaller Italian city, Fano (pop. 60,000), in 2024. The reason mid-sized cities are susceptible is unclear; large, densely populated cities such as Paris, Zagreb and Vienna are also highlighted as potential future hotspots.

The researchers indicate that these diseases are transported first by human hosts who have visited areas where the diseases are endemic – for example the explosion of chikungunya cases in France in 2025 was traced to an outbreak in La Réunion, French oversea territory in the Indian Ocean. Mosquitoes in France that bit infected humans then transmitted the disease locally, causing autochthonous cases.

Increased autochthonous transmission is being made possible by expanding conditions that favour the transmission of mosquito-borne diseases: warm temperatures reduce the extrinsic incubation period of pathogens (the time it takes for them to multiply sufficiently and become infectious to other hosts). The modelling indicates that the area at risk of dengue transmission has recently extended from the Mediterranean coasts up to northern Spain and western France. 

However, while the Asian tiger mosquito range is growing rapidly in France – at a rate of 10-40 km per year – it is approaching the limits of its theoretical climate niche here, note the researchers. In addition, while their range is generally widening, mosquito numbers may in fact have dropped in some places over the study period. For instance, in the model, the warm Mediterranean region saw a decrease in mosquito density, perhaps due to high summer temperatures. They thrive in warm, humid conditions with temperatures between 24 and 35C – above this and in dry conditions, they may become dehydrated and less able to feed, mate and ley eggs. 

The researchers acknowledge that the model does not correlate with empirical observation in some cases. For example, it predicts high suitability in the southern Iberian Peninsula, but the species has not yet been reported here. This discrepancy could be due to differing actual aridity and rainfall conditions to those considered in the modelling framework, suggest the researchers, or to the slow process of species arrival, adaptation, and colonisation.

The researchers also note that this species has remarkable adaptive capabilities, therefore colonization patterns may rely on progressive adaptation to new environments which is difficult to predict. The researchers therefore call for epidemiological surveillance data to be shared with academic researchers, to inform simulations of mosquito adaptation and spread. This data is especially pertinent in newly suitable areas for Asian tiger mosquito establishment, and the researchers recommend that surveillance and control measures focus on the ‘newly suitable’ areas identified in this study. 

Reference:

Radici, A., Hammami, P., Cannes, A., L’Ambert, G., Lacour, G., Fournet, F., Garros, C., Guis, H., Fontenille, D., and Caminade, C. (2025) Aedes albopictus Is Rapidly Invading Its Climatic Niche in France: Wider Implications for Biting Nuisance and Arbovirus Control in Western Europe. Global Change Biology 31(8). https://doi.org/10.1111/gcb.70414