On July 21, 2025, ARS Auvergne-Rhône-Alpes published a press release to report a second case of Aboriginal dengue in Saint-Chamond, in the Loire, confirming an upward trend in the unprecedented development of arboviroses because of the now essential presence of the famous mosquito-tiger, now present in 81 departments, or 84 % of the metropolitan territory.
Since the beginning of January 2025, Public Health France has already listed more than 500 cases imported from dengue on the whole of mainland France. These cases mainly concern travelers returning in particular from the Antilles, from South America or Asia. But since June, it is the Aboriginal transmission episodes that have worried health authorities: 13 chikungunya and dengue transmission homes have already been identified.
If the fear of a massive epidemic is not for the moment on the agenda, epidemiologists agree that this will undoubtedly be the case in a few years, due to global warming. And these current contaminations are only the beginnings.
This new Aboriginal case of dengue
The contaminated person has not traveled recently, which means that he was infected on the spot, in the same geographical area as the first case detected a few days earlier. This is the second indigenous case of dengue identified this year in Saint-Chamond, in the Loire and in Auvergne-Rhône-Alpes.
“At this point, it is not possible to establish a link with the 1st Aboriginal case identified in Saint-Chamond”specifies ARS Auvergne-Rhône-Alpes. An epidemiological survey is underway to determine if there is a link between the two cases, although nothing attests for the moment
According to the ARS, this new case has been identified in a sector close to the first, which led the health authorities to strengthen the surveillance measures and to trigger a demoustication operation within a perimeter of 150 meters around the places frequented by the infected person. Agents have also gone to meet residents to identify possible suspicious cases, while recalling the good gestures of prevention against mosquito bites.
An upward trend for several years
Each summer, dengue is returning via travelers returning from endemic countries. And the figures give the measurement of the phenomenon: since 2015, Public Health France has identified each year at least 500 imported cases. This figure has climbed strongly since 2020, exceeding 1,100 cases imported in 2023, and already 581 in 2025 to July 15, according to the latest epidemiological bulletin in public health France.
In parallel, indigenous cases, nonexistent ten years ago, became a reality: the first local household was detected in 2010, then some isolated cases were reported between 2015 and 2018. Their number has since exploded, with 66 cases identified in 2022, 45 in 2023, and up to 82 in 2024.
The reasons? With the intensification of international trips, the tiger mosquito more present than ever on the whole territory and an increasingly conducive climate for its proliferation, the risks of local transmission of the virus increase each year.
How to recognize the symptoms of dengue?
The symptoms of dengue generally appear between 4 and 7 days after the bite of an infected mosquito. In many cases, the disease can be benign, even asymptomatic. But when the symptoms manifest, they can be impressive.
There is a high fever (often above 38.5 ° C), accompanied by intense headaches, especially behind the eyes. Joint and muscular pain, sometimes very violent, appear, hence the nickname “tropical flu” or even “packet fever”.
Nausea, vomiting, extreme fatigue and rashes can also occur. Dengue can therefore easily be confused with other viral infections, hence the importance of quickly consulting a healthcare professional if these symptoms are presented after a stay in risky areas, or in a region where indigenous cases have been detected.
In 1 to 5 % of cases, the disease can evolve towards a more serious form called severe dengue. It manifests itself by bleeding, a brutal fall in blood pressure, intense abdominal pain, persistent vomiting or great agitation. This serious form requires emergency hospitalization, because it can be fatal if it is not treated quickly.
What to do in case of suspicion of dengue ?
As soon as the symptoms appeared above, the priority is to consult a doctor and report any recent stay in the infested zone of tigers mosquitoes, even without a trip abroad.
The diagnosis can be confirmed by a blood test. DEENGE being a compulsory declaration disease, health professionals must inform ARS to allow rapid management and prevention actions in the entourage.
A person infected with dengue can transmit the virus to a tiger mosquito that would bite it. This mosquito can then contaminate other people. This is why it is crucial, in the event of confirmed diagnosis, to protect yourself from bites for several days: wearing of covering clothes, use of skin repellents, installation of mosquito nets.
Likewise, it is strongly recommended to eliminate all the larval lodges around his home. The tiger mosquito lays its eggs in small amounts of stagnant water: cups, vases, clogged gutters, children’s toys … All these places must be emptied and cleaned regularly.
NAMELY
It is important to distinguish two types of dengue when we talk about the situation in mainland France. The imported cases are cases contracted abroad, generally in tropical areas where the virus is actively circulating-Antilles, Southeast Asia, Latin America … These cases do not present in itself danger for the local population as long as they do not meet a tiger mosquito ready to transmit the virus. On the other hand, indigenous cases, like those reported in Saint-Chamond, are those where the sick person has not left the territory. This means that the virus has been transmitted by a locally infected mosquito, which constitutes an additional step in the sustainable installation of dengue in mainland France.
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