Dengue virus in mainland France: What can we expect this year?
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Yannick Simonin, University of Montpellier
According to all experts, 2022 was an exceptional year in mainland 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 simply an anomaly for our country, which is not typically 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 affected area. Unlike “imported” cases from abroad, this means that the virus is circulating within the country.
This came as no great surprise: dengue fever, the most widespread arboviral disease in the world, which affects between 100 and 400 million people each year, has already been responsible for locally transmitted 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 thirty cases since 2010. So, initially, there wasn’t really much cause for concern.
But as it turned out, 2022 did not go as planned, and local transmission cases began to emerge one after another. Nine outbreaks of local dengue transmission 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 transmitted 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 transmitted case of dengue fever was identified in France in 2010 in the Alpes-Maritimes department.
However, dengue fever is a disease that should not be taken lightly.
Dengue fever, 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.
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In other symptomatic individuals, the disease mainly presents with symptoms similar to those of the flu: fever, headache, 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 human toll, managing 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 methods of control?
When an infected mosquito bites a host, the virus multiplies within its body. The next time it bites, the virus enters the bloodstream of another person, 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 target 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 a variety of factors.
It is therefore difficult to know whether 2023 and the years that follow will be similar to, or even 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, there is nevertheless a high probability 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 arbovirus transmission in mainland 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 synonymous with an unprecedented dengue epidemic: Peru is experiencing the most intense 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 period during which mosquitoes are active—a period that currently peaks from May to September. In addition, high temperatures promote the replication of viruses within mosquitoes and thus their transmission.
Surveillance networks stretched to their limits
Although it represents an all-time high, the number of dengue cases reported in 2022 is 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 expertise—including veterinarians, clinicians, entomologists, and researchers—who all contribute to a better understanding of these viruses.
However, last year’s surge in cases has put local resources under severe strain, as have mosquito control programs, which are operating at full capacity. This situation highlights the need for greater investment in these areas. We must start preparing today so that we are better equipped to manage future outbreaks. In this sense, 2022 is 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.