Dengue Virus in Metropolitan France: What Can We Expect This Year?
Vacations don't always go as planned… In our series “A Week from Hell!”, we break down what can go wrong—from travel sickness that’s worse when heading out on vacation to mosquito bites that can now transmit tropical viruses, not to mention the little-known microbiological hazards in hotels, “traditional” sunburns, or the unexpected dangers… of gardening, if you thought you’d be staying quietly at home.
Yannick Simonin, University of Montpellier
According to all experts, 2022 was an exceptional year in metropolitan France in terms of the circulation of arboviruses—viruses transmitted by blood-feeding arthropods, such as ticks and mosquitoes.
Does this year foreshadow what lies ahead? Or is it rather an anomaly for our country, which is not usually affected by these viruses—which are generally considered “exotic”?
2022: A Record-Breaking Year in Metropolitan France
Let’s rewind. In the middle of summer 2022, the first “locally acquired” case of dengue transmission was reported in France. This term refers to an infection detected within the country’s borders, without the patient having previously traveled to an infected area. Unlike “imported” cases from abroad, this means that the virus is circulating within the country.
This came as no great surprise: dengue, the world’s most widespread arboviral disease, which affects between 100 and 400 million people each year, has already been responsible for locally acquired cases in mainland France in recent years. The virus had been detected in particular in the Alpes-Maritimes, Var, Bouches-du-Rhône, Hérault, and Gard departments, with a total of about 30 cases since 2010. So, initially, there wasn’t really any cause for concern.
But 2022 did not go as planned, and locally acquired cases began to emerge one after another. Nine outbreaks of locally acquired dengue were recorded, totaling 66 cases, in the regions of Occitanie (12 cases), Provence-Alpes-Côte d’Azur (52 cases), and Corsica (two cases). In addition, the virus spread to new departments where no cases of dengue had ever been identified, such as Haute-Garonne, Hautes-Pyrénées, and Pyrénées-Orientales.
Sixty-six locally acquired cases may not seem like much, but that figure represents, in a single year, more than double the number of cases recorded over a 12-year period, since the first locally acquired case of dengue was identified in France in 2010 in the Alpes-Maritimes department.
However, dengue is a disease that should not be taken lightly.
Dengue, a potentially serious illness
Although dengue is asymptomatic in a large proportion of cases (50% to 90%, depending on the study), it can nevertheless lead, in about 1% of cases, to a potentially fatal form: so-called “hemorrhagic” dengue, which is accompanied by multiple bleeding episodes, particularly gastrointestinal, cutaneous, and cerebral bleeding.
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In other symptomatic individuals, the disease mainly presents with symptoms quite similar to those of the flu: fever, headaches, muscle aches… It is estimated that each year, 500,000 people worldwide are hospitalized for severe forms of the disease, resulting in between 10,000 and 15,000 deaths. Beyond this loss of life, treating the disease imposes a significant cost on the community.
It is important to limit the number of cases, because the disease can spread with every mosquito bite.
What are the ways to combat this?
When a mosquito carrying the virus bites an infected host, the virus multiplies in the host’s body. The next time the mosquito bites, the virus will enter another person’s bloodstream, where it can be picked up by another mosquito, and so on.
The best way to limit the spread of an outbreak is therefore to combat the virus’s primary vector: Aedes albopictus, better known as the tiger mosquito.
This is a very complicated task, as the range of this mosquito has been steadily expanding in France in recent years, significantly increasing the number of departments at risk.
Each identified outbreak requires the implementation of a fairly extensive infrastructure to break the cycle of viral transmission in the human population: mosquito control operations near detected cases (to eliminate adult mosquitoes and their larvae), public awareness campaigns targeting the general public and healthcare professionals, and door-to-door surveys conducted in collaboration with the Regional Health Agencies (ARS), Santé publique France, and mosquito control agencies (Altopictus or the Interdepartmental Mosquito Control Association).
What can we expect in the coming years?
It is very difficult to predict the spread of arboviruses, as their transmission cycle is influenced by multiple factors.
It is therefore difficult to know whether 2023 and the years that follow will be much the same—or worse—than 2022. It is also difficult to predict which arbovirus—dengue, Zika, or chikungunya—will take center stage. Since dengue is the most widespread arbovirus globally, it is nevertheless highly likely that we will see an increasing number of cases of this disease in mainland France in the coming years.
One thing is certain: it is now clear that we should expect an increase in cases of arboviral transmission in metropolitan France over the coming summers. This is all the more true given that the exceptional situation observed in France last year is not an isolated case on a global scale.
In the Americas, 2.8 million cases of dengue were identified in 2022, more than double the number of cases reported in 2021. And for some countries, 2023 is already marked by an unprecedented dengue epidemic: Peru is experiencing its most severe outbreak since the disease reemerged in the country in 1990.
Another cause for concern is that the World Health Organization is preparing for the possibility that the El Niño phenomenon, expected in 2023 and 2024, could increase the transmission not only of dengue but also of other arboviruses.
Finally, climate change will also affect the proliferation of mosquitoes that carry these diseases by extending the mosquitoes’ active season, which currently peaks from May through September. Furthermore, high temperatures promote the replication of viruses in mosquitoes and thus their transmission.
Surveillance networks at the limits of their capacity
Although it represents an all-time high, the number of dengue cases recorded in 2022 is therefore likely still very limited compared to what we can expect in the coming years. Furthermore, France will host major sporting events in the coming years, including the 2024 Olympic Games, which could contribute to increasing the spread of arboviruses…
In response to the emergence of these arboviral diseases, France has established active surveillance networks. These networks bring together experts with diverse areas of expertise (veterinarians, clinicians, entomologists, researchers), all of whom contribute to a better understanding of these viruses.
However, last year’s surge in cases put local resources under severe strain, as did mosquito control programs, which are operating at the limits of their capacity. This situation highlights the need for greater investment in these areas. We must begin preparing today so that we are better equipped to control future outbreaks. In this sense, 2022 serves as a warning that we must all take seriously…
Yannick Simonin, virologist specializing in the surveillance and study of emerging viral diseases. University Professor, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.