Dengue fever affects tropical regions, but lately the disease is experiencing a resurgence in parts of southern Europe, spreading among populations and reaching areas where it had not been reported before.
The mosquito-borne disease, which can cause fever, headache and fatigue and kills up to 40,000 people each year, is not endemic in continental Europe. Most cases or small outbreaks come from inflamed travelers bringing the virus back. But this year, a combination of warm weather conditions and a surge in imported cases has led to an increase in local infections transmitted by the tiger mosquito (Aedes albopictus), which inhabits southern Europe.
“This is something that deserves a lot of attention,” says Patricia Schlagenhauf, an epidemiologist at the University of Zurich in Switzerland.
Nature asked the researchers how worrisome the challenge was and whether the risk could worsen in the future.
According to the researchers, several points contribute to the accumulation of locally transmitted dengue cases. The recovery of foreigners after the COVID-19 pandemic has brought more cases back from dengue-endemic areas. As of 27 October, France had reported 1,414 imported cases of dengue; In 65% of cases, Americans came from Martinique (550) and Guadeloupe (369). In contrast, only 217 imported cases were reported in 2022 and 164 in 2021.
The presence of A. albopictus mosquitoes capable of transmitting the virus means that when inflamed travelers are bitten on their return, those insects now carry the virus into their blood and can transmit the disease to others they bite.
These mosquitoes thrive in temperatures between 15°C and 35°C and can breed in small amounts of standing water. “All you have to do is have a container for your plants on your balcony with water. It’s a wonderful position for adults to race,” Schlagenhauf says.
“At the moment, all of that exists in southern Europe. There are a lot of returning travelers, there is a local mosquito that can transmit the virus, and there is also the right climate and temperature,” he adds.
As of Oct. 25, 105 transmitted cases had been reported in southern Europe, totaling 66 in Italy, 36 in France and 3 in Spain, according to the European Centre for Disease Prevention and Control.
The local outbreak in Italy, which has the largest population of A. coli, is a local outbreak in Italy. albopictus of Europe, concentrated around the regions of Lombardy and Lazio and included 28 cases in Rome.
In France, the number of locally transmitted cases is so far lower than in 2022, but outbreaks have now spread to the Auvergne-Rhône-Alpes and Île-de-France regions, areas that in the past had not reported any cases of local transmission. .
Given that 50% to 90% of Americans are asymptomatic, the actual incidence of dengue is likely to be higher than reported. ” Through a door-to-door investigation, we learned of several indigenous cases who had consulted their GP, but their doctors did not prescribe the [correct] biological tests for dengue,” says Frédéric Jourdain, an epidemiologist at the Montpellier-based Public Health France. agency. There is still a desire to raise awareness among fitness professionals. “
Locally transmitted cases in Europe tend to be sporadic and seasonal, peaking in late summer and early autumn and shortening the winter months. ” I don’t think it’s going to replace it anytime soon on the European continent, I don’t think it’s going to become a permanent problem,” says Christina Frank, an infectious disease epidemiologist at the Robert Koch Institute in Berlin.
For dengue to become endemic in Europe, the virus would have to become established in the local mosquito population. This means that an inflamed female mosquito will have to transmit the virus to her eggs, so that by the time the eggs hatch, the offspring are already inflamed. “From a clinical standpoint, it’s not impossible,” Jourdain said. “But such a thing is quite rare” and occurs regularly in spaces where outbreaks are much larger each year.
“What we are seeing in Europe is an emerging problem. But it’s obviously different from the dengue burden in tropical regions. Therefore, it will remain an imported pathology, a non-endemic [disease],” Jourdain said. “Will we have a virus [dengue] better suited to Aedes albopictus?For me, it’s still a matter of study.
This year’s long, hot summer in Europe has created ideal conditions for mosquitoes to thrive. Albopictus thrive and colonize giant urban areas.
Mosquitoes, which can also transmit viruses such as chikungunya and Zika, have “a longer period of activity and can accumulate larger populations if the summer is longer,” Frank says. “And they can also live a little farther north than they would otherwise. “”
“The time between human instances can be reduced, processes in the mosquito can be accelerated, and there is more time for an outbreak to develop,” he adds.
The species has recently been discovered in 20 European countries and is expected to establish itself in northern and western Europe over the next few decades, in addition to Belgium, the Netherlands, parts of Germany, and the southernmost regions of the United Kingdom. “It’s an extremely adaptable mosquito” because of its genetic diversity, says Didier Fontenille, an entomologist at the Montpellier Research Institute for Development. But it takes several years to create an adequate mosquito population, he adds.
Dengue fever is on the rise worldwide, with more than 4. 2 million cases reported in 79 countries as of Oct. 2. The Americas are experiencing one of the most incidents since 1980. Chad reported its first outbreak in August, and Bangladesh, where dengue fever is endemic, has recorded nearly seven times as many cases this year as it did in 2018.
“This necessarily triggers more inflamed populations and a greater threat of those viruses reaching well-connected areas,” says Moritz Kraemer, an epidemiologist at the University of Oxford in the United Kingdom. “The more imports we see, the more opportunities there are for local transmission,” he adds.
Current global efforts to combat dengue outbreaks come with the arrival of mosquitoes inflamed with Wolbachia, a bacterium that prevents the insect from transmitting viruses. The technique produced promising effects when tested on Aedes aegypti mosquitoes in Yogyakarta, Indonesia, and in three cities in Colombia. But since the A. albopictus mosquito naturally carries two strains of Wolbachia, the scenario is more difficult.
It’s me: https://doi. org/10. 1038/d41586-023-03407-6
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