The ‘exotic’ dengue disease is biting Europe hard, warn experts

One day in October, 2013, Imran Shah came down with a fever. A few weeks earlier, Karachi, Pakistan’s largest city, was battered by heavy monsoon rains. Small pools of stagnant green-black water dotted the potholed streets And the mosquito-borne dengue fever raced across the metropolis of more than 20 million people.

The symptoms of Dengue include high fever, severe headache, muscle and joint pains, and skin rash. While most cases result in mild illness, a small proportion can develop into a life-threatening condition called dengue hemorrhagic fever.

Shah, now 38, says his condition worsened quickly after he started experiencing the symptoms. By the time he was admitted to a hospital a day later, his platelets -the cells in our bodies that help patch up open wounds - dropped to dangerous levels.

“I lost my job in a start-up since it took five to six months to recover completely from Dengue. I couldn’t eat anything solid for several weeks, and lost my physical strength,” he tells TRT World in a recent interview.

His family had to spend a small fortune on his treatment at a private hospital. But Shah was among the lucky ones.

Dengue fever kills tens of thousands of people every year in low and middle-income countries including Bangladesh, India, Pakistan and Thailand.

This year, Brazil is struggling to control a dengue fever outbreak with more than one million cases already recorded.

Dengue fever, which spreads when an infected mosquito bites a human, is one of 20 neglected tropical diseases, which according to the World Health Organization (WHO) don’t figure prominently in the global health agenda.

Tropical diseases like dengue are associated with impoverished countries. That's one of the reasons these illnesses, which affect more than a billion people, haven’t received required funding.

Since dengue fever has remained a problem for poor countries for a long time, multinational pharmaceuticals, with their head offices located in Europe and the US, haven’t devoted resources to finding a cure. Prevention instead of intervention remains the standard way to deal with dengue fever.

But in recent years, the Aedes albopictus mosquito, also known as the Asian tiger mosquito, native to Southeast Asia's tropical and subtropical regions, has taken a liking for European blood.

No longer a far-flung issue

“Dengue is creeping towards Europe. It's not just a problem of the endemic countries anymore,” says Dr Dinu Guruge, Consultant for the Dengue Global Program at Drugs for Neglected Diseases Initiative (DNDi).

She says the effects of climate change, such as global warming, and factors like increased global travel and migration are responsible for dengue’s spread.

“Warmer weather conditions in Europe due to global warming can now provide suitable temperatures for dengue mosquitoes to breed and transmit the virus,” said Guruge.

Last year, Europe registered 122 dengue fever cases. All of them were locally transmitted, which means patients didn’t acquire them while traveling to other countries.

According to the European Center for Disease Prevention and Control (ECDC), dengue is not entirely unfamiliar to Europe. It was endemic in the southern part of the continent until 1930.

Aedes aegypti, another member of the dengue-spreading mosquito family with black and white stripes, caused multiple epidemics in Greece and Türkiye, affecting over a million people. However, it vanished in the 1950s.

Recently, indigenous outbreaks of dengue have been reported in France, Croatia, Italy and Spain.

However, ECDC’s Principal Expert on emerging and Vector-Borne Diseases, Céline Gosner, tells TRT World that the current situation is not too disquieting but requires immediate cognisance.

"I would not say today it's alarming, but we need to pay attention and look at it carefully since the situation could change,” she says.

“Dengue fever is still a relatively unknown disease in Europe. It is still considered an "exotic disease" rather than a possible local health concern.

Therefore, more work must be done to increase public awareness.”

It’s summer time…to bite

For people in South and Southeast Asia, it’s not unusual to come across local officials with foggers spraying clouds of white smoke as they fumigate the streets after a rainy season. But now it’s also becoming a common site in European cities.

Warmer temperatures favour dengue-carrying mosquitoes, helping them to breed and transmit the virus. DNDi’s Guruge says the disease spreads when mosquitoes bite people mostly in early morning or during sunset.

Aedes aegypti, the mosquito with black and white stripes, loves rain especially if it can find a breeding ground over stagnant water on a windowsill, in a flower pot or on in a roof caveat.

Dengue can travel from tropical and sub-tropical regions to Europe through cargo holds on aircraft or ships if carrying standing water that allows immature mosquitoes to survive and emerge as adults at destination ports, says Nadja Hedrich, a researcher working on the project "Infection Tracking in Travellers" (ITIT) at the University of Zurich.

One theory goes that the infected mosquitoes travelled from tropical Asia in the inside hollow part of used tires that were increasingly being transported on container ships in the 1970 and 80s.

The disease has an extremely low chance of spreading in winter, which is why Dengue fever cases are rare in Northern European countries like Norway, Finland, Denmark, Iceland and Sweden, experts said.

“Colder winters in Europe prevented mosquito breeding and virus transmission. However, with climate change causing milder winters, which may now sometimes be warm enough for limited mosquito breeding and a risk of isolated virus transmission,” says Guruge.

Dengue travels light

ECDC says European countries recorded 11,478 travel-related dengue cases between 2015 and 2019. The infection prevalence was highest among travellers returning from Asia (71 percent), primarily from Southeast Asia.

“The conditions in Europe are becoming more favourable for these mosquito species to stay over winter and become endemic here,” says Hedrich of ITIT.

Since restrictions have been eased, people are travelling more frequently across borders after the COVID-19 epidemic.

“Increased travel provides more opportunities for dengue virus in infected people and mosquitoes carrying the virus to spread between locations,” says Hedrich.

WHO says that dengue cannot be directly transmitted from one person to another. It is only transferred when a female Aedes mosquito bites an infected patient and then transfers the virus to a healthy person.

Hedrich found that in some cases dengue can also spread through blood transfusion and organ donation. For instance when an organ is transplanted from a donor who is infected with the virus, even even if he or she is not showing any visible symptoms.

“It is still very rare for dengue to spread through blood and organs in Europe, but if the number of cases continues to rise, it would be worth investigating to see whether blood and organs are tested for Dengue in Europe.”

Prevention and control

Since dengue fever is still a lesser-known disease in Europe, experts say there’s a need for large-scale awareness campaigns and exhaustive research to control its spread.

“There is no specific treatment for dengue, and there is a lack of research and funding to develop medicines adapted to the countries' needs,” says DNDi’s Guruge.

“The most effective prevention is not to get bitten by a mosquito, which is impossible since we can not isolate mosquitoes and people in separate rooms. Therefore, individual and large-scale measures are required to control Dengue’s spread in Europe.”

Dengue is a mandatory notifiable disease at the ECDC. It has data on travelers who return to Europe diagnosed with Dengue and also locally transmitted cases.

“Dengue is an emerging disease in Europe, therefore we don't have much background data to compare with, but based on what we have today, we expect to see a continued increase in the number of cases in the following summer and larger outbreaks,” says ECDC’s Gosner.

And since Europe has still some way to go before catching up with the disease, ITIT’s Hedrich says it will be better to look east at the tropical and sub-tropical endemic nations and learn from their experience on to contain dengue fever.