Tropical Mosquitoes Are Bringing Dengue to Europe's Doorstep

When Tropical Diseases Go Global

In September 2024, something unexpected happened in Fano, Italy. Patients started arriving at the emergency room with a rash on their hands and feet, fever, nausea, and diarrhea. The diagnosis? Dengue fever, a disease typically confined to tropical regions. The catch: none of these patients had recently traveled anywhere. They’d simply visited the same neighborhood in this coastal Italian city.

By October, 199 cases had been detected in the area. Dengue was spreading locally in mainland Europe, a place most residents associate with mosquitoes as nothing more than summer nuisances.

This isn’t an isolated incident. Over the past few years, European countries have reported outbreaks of chikungunya, West Nile virus, and other mosquito-borne diseases that were previously thought of as tropical concerns. The culprit is clear: climate change. As temperatures rise, invasive mosquitoes are establishing permanent populations across the continent, and the viruses they carry are coming along for the ride.

Meet the Tiger Mosquito

The main character in this story is the Aedes albopictus, commonly known as the Asian tiger mosquito. Unlike most mosquito species, it bites during the day as well as at night. It thrives between 20 and 30 degrees Celsius (68 to 86 Fahrenheit), but can survive at temperatures around 10 Celsius (50 Fahrenheit) or even lower.

“This means there are already conditions that could allow for the spread of the Asian tiger mosquito even in England,” says Riccardo Moretti, a senior researcher at the Italian National Agency for New Technologies, Energy and Sustainable Economic Development, who has studied tiger mosquitoes for over 20 years.

The tiger mosquito already has established populations across southern Europe and is moving north. What’s more alarming is that recent research found these mosquitoes can transmit chikungunya at just 14 degrees Celsius (57 Fahrenheit), two degrees cooler than previously thought. “That difference of two degrees matters a lot when we are talking about global warming,” explains epidemiological modeler Sandeep Tegar.

The Perfect Storm for Disease Spread

Currently, most mosquito-borne disease cases in Europe occur at the end of summer when tiger mosquitoes peak and travelers unknowingly bring viruses home. A mosquito bites an infected person, then spreads the disease to others. As temperatures drop, mosquito activity declines and cases subside.

But if the mosquito season extends, as researchers predict it will, the implications become serious. Moretti warns of a scenario where tropical diseases like dengue become endemic in parts of Europe, meaning they’re always present. “It is completely different dealing with occasional cases of virus transmission and instead dealing with a permanent status of possibility of transmission,” he says.

Temperature tells only part of the story. Excessive heat above 35 degrees Celsius (95 Fahrenheit) actually stresses tiger mosquitoes, which is why southern France and Spain experienced fewer mosquitoes during recent heat waves. Rain and humidity also matter enormously. Mosquitoes need standing water to breed, but too much rain washes away breeding sites while too little means insufficient breeding grounds. The interplay of climate, tech, human behavior, and viral biology makes predicting disease patterns extraordinarily complex.

Fighting Back

Some innovative approaches exist. Researchers have tested releasing millions of reproductively incompatible male mosquitoes that sterilize females’ eggs when they mate, significantly reducing fertile populations. But breeding these in specialized facilities is expensive and logistically challenging.

The real advantage Europe has is its public health infrastructure. “A common misconception is that preparedness is mainly about predicting disease outbreaks,” says Felipe Colón González, an expert in climate and infectious diseases. “In reality, preparedness is about building the system that allows public health infrastructure to effectively react when risks emerge.” This explains why European case counts remain lower than in other regions with similar climates.

For now, the practical approach mirrors what people in tropical regions have done for decades: mosquito nets, emptying standing water from flower pots, using repellent, and wearing long clothing during evening hours. It’s a significant shift in lifestyle for a continent that never had to worry about such precautions before.

As the yellow fever mosquito already establishes itself in Cyprus and Madeira, one reality becomes impossible to ignore: Europe’s mosquito problem isn’t going away, and neither are the diseases they carry.

Source: WIRED