Rising heat spreading mosquito-borne diseases across Europe

Data collected by the European Centre for Disease Prevention and Control (ECDC) has revealed a continuing upward trend within the European Union of a number of cases of dengue, imported from dengue-endemic regions, as well as an increasing number of local outbreaks of West Nile virus infections.

Dengue (break-bone fever) is a viral infection that spreads from mosquitoes to people. It is more common in tropical and subtropical climates. Most people who get dengue will not have symptoms. But for those who do, the most common symptoms are high fever, headache, body aches, nausea, and rash.

In 2023, there were 130 locally acquired cases of dengue reported in the EU/EEA, and 71 cases were reported in 2022 – a significant increase compared to the ten-year period 2010-2021, where the total number of locally acquired cases was 73 for the whole period.

Imported cases are also on the rise with 1,572 reported cases in 2022 and over 4,900 cases in 2023. This is the highest number of imported dengue cases reported since the start of the surveillance at the EU level in 2008.

In the first months of 2024, several countries have reported substantial increases in number of imported dengue cases, which could suggest that the numbers in 2024 might become even higher.

“Europe is already seeing how climate change is creating more favourable conditions for invasive mosquitos to spread into previously unaffected areas and infect more people with diseases such as dengue,” said ECDC director Andrea Ammon.

“Increased international travel from dengue-endemic countries will also increase the risk of imported cases, and inevitably also the risk of local outbreaks.

“Personal protective measures combined with vector control measures, early detection of cases, timely surveillance, further research and awareness-raising activities are paramount in those areas in Europe most at risk.”

As of 2024, Aedes albopictus is established in Austria, Bulgaria, Croatia, France, Germany, Greece, Hungary, Italy, Malta, Portugal, Romania, Slovenia, and Spain, and it is introduced in Belgium, Cyprus, Czechia, the Netherlands and Slovakia.

Aedes albopictus, known for transmitting dengue, chikungunya, and Zika viruses, is spreading further north, east, and west in Europe, and now has self-sustaining populations across 13 EU/EEA countries.

Aedes aegypti, a vector of yellow fever, dengue, chikungunya, and Zika viruses recently established itself in Cyprus. Its potential for establishment in other parts of Europe is concerning due to its significant ability to transmit pathogens and its preference for biting humans.

It is widely anticipated that climate change will largely impact the spread of mosquito-borne diseases in Europe, for instance, through the creation of environmental conditions favourable for the establishment and growth of mosquito populations.

In 2024, a confirmed locally acquired human case of West Nile virus infection with onset of symptoms at the beginning of March was reported in Seville, Spain. Although an isolated case, it highlights that the transmission of West Nile virus can occur very early in the year, likely due to suitable climatic conditions.

The ECDC said that simple measures such as removing stagnant water in gardens or balconies where mosquitos breed should be advertised to the population.

Personal protective measures to reduce the risk of mosquito bites include the wearing of clothes that cover most of the body, the use of mosquito repellent, the use of mosquito bed nets or window/door screens and sleeping or resting in air-conditioned rooms.

“For these to be widely applied, effective awareness-raising campaigns among the general public are essential,” the ECDC said.

“Enhanced surveillance and early detection of travel-related and locally acquired cases of mosquito-borne diseases remain essential to implement timely and appropriate vector and disease control measures.”

Since 2010, which is when the first recent dengue outbreak was recorded, 48 vector-borne dengue outbreaks have occurred. Between 2010 and 2017, there were up to 3 outbreaks per year, 5 outbreaks in 2018, 7 in 2020, 10 outbreaks in 2022, and the peak was observed last year in 2023, with 8 outbreaks in France, 4 in Italy and 2 in Spain.