Dengue in Europe is no longer a travel-only problem. In Fano, Italy, doctors investigating patients with fever, rash, nausea and diarrhea in September 2024 found dengue infections in people who had not recently visited countries where the virus is common, according to testing later reported in Eurosurveillance. The common link was a neighborhood in the coastal city.
The Fano cluster became one of the clearest warning shots yet: 199 locally acquired dengue cases were identified between mid-August and mid-October 2024. Researchers cited by WIRED say warmer European seasons are giving invasive mosquitoes more time and territory to spread viruses that used to be treated mainly as imported risks.
Why is dengue spreading in Europe?
The main vector now is Aedes albopictus, better known as the Asian tiger mosquito. Riccardo Moretti, a senior researcher at Italy’s ENEA, told WIRED the species has established itself across Europe, especially in the south, and is expected to push farther north as conditions warm.
The mechanism is not exotic. A person can return to Europe carrying dengue after being infected elsewhere. If a local tiger mosquito bites that person and later bites others, the virus can start moving through a neighborhood. That is local transmission, and it is the part public health agencies care about before it becomes routine.
Tiger mosquitoes bite during the day as well as at night, which makes them more annoying than the standard bedtime mosquito villain. Moretti said they do best between 20 and 30 degrees Celsius, or 68 to 86 degrees Fahrenheit, but can survive around 10 degrees Celsius. He said even England already has seasonal conditions that could support spread during the warmest months.
Farther south, the season is stretching. In Greece, Moretti said researchers have found adult tiger mosquitoes active as late as December and returning in March, with eggs surviving winter. He warned that parts of Europe could eventually face year-round transmission risk, a different public health problem from sporadic imported cases.
Chikungunya is also getting more room to move. Sandeep Tegar, an epidemiological modeler at the UK Centre for Ecology and Hydrology, led a study finding that tiger mosquitoes can transmit chikungunya at 14 degrees Celsius, not 16 degrees as previously thought. That two-degree shift expands the potential outbreak window across much of Europe.
What keeps mosquitoes from spreading everywhere?
Heat helps mosquitoes only up to a point. Frederic Bartumeus, an ecologist at Spain’s CEAB research center, told WIRED that temperatures above 35 degrees Celsius, or 95 degrees Fahrenheit, can hurt tiger mosquito survival. He said recent hot, dry conditions in southern France and Spain may mean fewer mosquitoes there this year.
Water is another constraint, and mosquito math is fiddly. Felipe Colón González, a climate and infectious disease expert at Wellcome, said too little rain leaves too few breeding sites, while heavy rain can flush them away. Standing water remains the key nursery: eggs are laid there, and larvae and pupae develop there.
Researchers are testing more aggressive controls. Moretti’s team recently released more than a million reproductively incompatible male tiger mosquitoes in Italy, causing females to lay sterile eggs and cutting the number of fertile eggs in the area. The catch, because there is always a catch, is cost: those males were bred in a specialized facility in Miami by Google’s Debug program and shipped to Italy.
Moretti said eliminating the species is not realistic because the mosquitoes colonize new areas efficiently. The aim is to cut transmission risk. Colón González said Europe’s public health systems need to react quickly when outbreaks appear, not treat prediction as preparedness. Reliable surveillance and information systems have so far helped keep European case counts below those in other regions with similar climates.
Another invasive mosquito is already in the queue. Aedes aegypti, the yellow fever mosquito, has established populations in Cyprus and Madeira, according to European disease surveillance data cited by WIRED. It can carry yellow fever, dengue, chikungunya and Zika. It tolerates cooler temperatures less well than the tiger mosquito, but has been found farther north after likely traveling on cargo, including at a service station in Luxembourg.
For residents, the advice is low-tech and familiar in warmer regions: use window screens or nets, empty standing water from places such as flower pots, wear repellent and cover exposed skin when mosquitoes are active. It is not glamorous. It is mosquito control, which rarely is.
This story draws on original reporting from WIRED.
