Nouvelle-Aquitaine: Indigenous dengue and chikungunya are making their way into the region: "These outbreaks were predictable"

With 20 cases of indigenous chikungunya in Nouvelle-Aquitaine since July, and two cases of dengue fever, the region is impacted by the epidemics raging in the Indian Ocean. Many cases are flying under the radar of the regional health agency.

F or the first time, Nouvelle-Aquitaine has recorded outbreaks of indigenous chikungunya and dengue fever. These viral diseases, transmitted by the bite of an infected tiger mosquito, did not concern us until this year. The spread of Aedes albopictus in France, fueled by global warming and epidemics affecting overseas regions—particularly Réunion and Mayotte—have a direct impact on the continent.

"Mosquitoes take the train, the plane, and the boat," Bordeaux-based infectious disease specialist Denis Malvy often points out, pointing out that globalization and travel facilitate the circulation of viruses. As of August 12, Public Health France counted 20 indigenous cases of chikungunya in Nouvelle-Aquitaine , including 14 cases in Val de Cognac (Charente), compared to 140 imported cases – travelers returning from overseas departments – and two indigenous cases of dengue fever in Langon (33) compared to 100 imported cases.

Dr. Robin Le Barreau, head of the health monitoring unit at the Nouvelle-Aquitaine regional health agency (ARS), admits that this situation was "expected." "We were prepared for the possibility of the emergence of indigenous cases, given the strong epidemic overseas and the links that unite us through travel. Until now, only the Provence-Alpes-Côte d'Azur and Occitanie regions had recorded indigenous cases. Among those diagnosed in the region, there have been no serious cases, no hospitalizations. However, we must remain vigilant and prevent contagion." The cases reported to the ARS are only the tip of the iceberg.

But how does a doctor diagnose chikungunya or dengue fever? "It's very complex, because the two viral diseases are similar. These diseases are notifiable, and all general practitioners know that they are responsible for filling out a form when they detect a case. The clinical signs of dengue fever resemble a flu-like syndrome, with fever and possibly joint pain, sometimes a rash. The signs of chikungunya fever correspond to a triad of fever, joint pain, and a rash. The diagnosis is only made after the results of a blood test."

When a person returning from overseas presents symptoms, a blood test to detect arbovirosis precedes the declaration to the ARS. Diagnosis for a person who has not traveled and presents the same symptoms is based on the same process. "Indeed," continues Dr. Le Barreau. "In the first case, that of the infected person returning from Mayotte or Reunion, after the declaration is transmitted by the general practitioner, the ARS sets up an epidemic and environmental investigation protocol, organizes an investigation to contain the outbreak. The infected person will be contagious two days before the symptoms and seven days after. They must isolate themselves to avoid being bitten by a tiger mosquito, which, by biting another person nearby, could infect them in turn. The mosquito's perimeter does not exceed 150 meters, it's not much. You just have to pass by."

The ARS systematically organizes a mosquito control campaign in the area affected by the infection.

Last July, the first case of indigenous regional chikungunya was reported to the Bordeaux Regional Health Agency (ARS). It involved a 5-year-old child living in Illats, Gironde.

Yet, a few weeks later, when another outbreak was detected on July 28 in Dax, Landes, the ARS clarified that Illats' child had not contracted the disease after all. Strange: "It's very rare," explains Dr. Le Barreau. "For each suspected case, two blood tests are performed to validate the diagnosis. In Illats' case, the first test did indeed detect chikungunya; the same sample was sent for double examination to the National Reference Center for Arboviruses in Marseille, which denied the claim."

The ARS's mission is to contain infection hotspots and prevent viral proliferation through the multiplication of infected mosquito bites. The first mosquito bites a sick person, then bites another nearby, infecting them. The latter can in turn be bitten by a mosquito during the nine days they are contagious, infecting a mosquito, and so on. "For now, the diseases are fairly mild, but many infected people with few or no symptoms are slipping under our radar. We know this, so we must protect ourselves as much as possible against the invasion of tiger mosquitoes ," concludes the ARS doctor.

For now, the illnesses are quite mild...