Dengue Outbreak in Fano Highlights Growing Threat of the Asian Tiger Mosquito in Europe

In September 2024, emergency-room physicians in the coastal city of Fano identified a cluster of patients with rash, fever, nausea and diarrhea. Laboratory testing confirmed dengue infection in all cases, despite none of the patients having traveled to endemic regions. All had visited the same neighbourhood, indicating local transmission. Health officials recorded 199 confirmed dengue cases between mid-summer and mid-autumn 2024, making this the largest locally acquired dengue event on the European mainland to date.

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The outbreak is linked to the Asian tiger mosquito (*Aedes albopictus*), an invasive species that thrives in daytime and night-time biting. The mosquito is already established across southern Europe and is expanding northward as average summer temperatures rise. It can survive in temperatures from about 10 °C (50 °F) up to 30 °C (86 °F), allowing it to persist in regions previously considered too cool.

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• Confirmed dengue cases in Fano: 199.

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• *Aedes albopictus* adults have been observed active from March through December, overwintering as eggs.

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• Recent research shows the mosquito can transmit chikungunya at 14 °C (57 °F), two degrees lower than earlier estimates, widening the potential geographic range.

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Riccardo Moretti, senior researcher at Italy’s National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), notes that current climate conditions already permit the tiger mosquito’s spread into England. “This means that at the moment there are already conditions that could allow for the spread of the Asian tiger mosquito, even in England,” — Riccardo Moretti He adds that a “concrete risk” exists for a year-round mosquito population within the next few years. “There is a concrete risk that in the next few years, we could have a population capable of surviving throughout the year,” — Riccardo Moretti Sandeep Tegar, an epidemiological modeler at the UK Centre for Ecology and Hydrology, emphasizes that a two-degree temperature shift dramatically alters disease-transmission potential. “That difference of two degrees matters a lot when we are talking about global warming,” — Sandeep Tegar

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If the mosquito season continues to lengthen, Europe could see more frequent and larger outbreaks of dengue, chikungunya, and other tropical viruses. Persistent, year-round mosquito populations would shift diseases from occasional imported cases to endemic threats, challenging public-health systems that are not yet equipped for continuous tropical-disease surveillance.

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