Dengue fever alert: the number of cases explodes in France, what we know about the situation

The tiger mosquito is now present in 70 departments and continues to make inroads in metropolitan France. Update on the situation.

Winter is approaching, yet they are still present: mosquitoes and especially tiger mosquitoes. Various health authorities have recently alerted to an increase in dengue fever cases in France. According to Public Health France, it would be more than three times higher than the maximum observed in 2020and the risk has spread “with the occurrence of outbreaks in departments hitherto spared”.

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What is dengue fever?

Also called “tropical flu”, dengue fever is an infectious disease caused by an arbovirus which is mainly transmitted by the tiger mosquito. Unlike the “classic” mosquito, this parasite is silent and bites at daybreak or dusk. In addition to dengue, it can be a vector for two other conditions: chikungunya and zika.

There are two kinds of dengue fever: classic and hemorrhagic. In the first case, the disease is characterized by high fever, headache, nausea, vomiting, joint and muscle pain, and a measles-like rash.

These signs occur suddenly after two to seven days of incubation. A brief remission is observed in the patient three to four days after the onset of the first manifestations, but this period is short-lived. The symptoms then intensify. The patient may then suffer from nosebleeds, conjunctival hemorrhages or bruises.

Dengue hemorrhagic fever is an acute and severe form of the disease. It affects 1% of dengue fever cases worldwide. It can cause serious complications such as persistent fever, multiple hemorrhages (gastrointestinal, cutaneous and cerebral), details WhyDoctor.

What explains this increase in cases?

According The Expressthe main reason for this outbreak is due to the Aedes albopictus, the tiger mosquito. Over the past twenty years, it has conquered more than two thirds of the French departments. With its black body and striped legs, this insect is a vector of many viruses such as dengue fever, Zika, chikungunya and yellow fever.

Other factors may also explain the increase in contamination: resumption of travel and the return of travelers from risk areas, as well as favorable climatic conditions for mosquito breeding with heat and rain.

“The summer we experienced, exceptional for its alternation of scorching heat and intense rainy episodes, especially in the southern regions, led to a significant increase in the number of mosquitoes (…)”, explained Yannick Simonin, virologist , lecturer in surveillance and study of emerging diseases, at the University of Montpellier, West France.

Santé Publique France details in this sense that the spread of infections transmitted by mosquitoes is strongly associated with global warming.

Which departments are most affected?

Currently, of the five departments affected by the disease, three are located in the region Occitania and two in the Provence-Alpes-Côte d’Azur region (Paca).

In Occitania, four cases have been identified in the same habitat, in the town of Salvetat Saint-Gilles, 20 km west of Toulouse, in Haute-Garonne; 3 cases have been reported in the commune of Andrest and that, 15 km away, of Rabastens-de-Bigorre, in the Hautes-Pyrénées; a case was detected in Perpignan, in the Pyrénées-Orientales. The dengue virus had never been identified in these last two departments.

In the Paca region, the two departments affected are the Var, with 7 cases identified in Fayence and, above all, the Alpes Maritimes with 31 cases identified in three municipalities located less than 10 km away from each other: Saint-Jeannet, Gattières and La Gaude, indicates West France.

On September 16, Public Health France told us: “This is the first time that cases have appeared in the Pyrénées-Orientales, Haute Pyrénées and Haute Garonne”.

67 departments colonized in 2022

As of January 1, 2022, Aedes albopictus was established in 67 metropolitan departments:

Ain, Aisne, Alpes de Haute-Provence, Alpes-Maritimes, Ardèche, Ariège, Aude, Aveyron, Bas-Rhin, Bouches du Rhône, Cantal, Charente, Charente Maritime, Cher, Corrèze, South Corsica, Côte d’Or, Deux-Sèvres, Dordogne, Doubs, Drôme, Essonne, Gard, Gers, Gironde, Haute-Corse, Haute-Garonne, Hautes-Alpes, Hautes-Pyrénées, Haute-Savoie, Haut-Rhin, Hauts-de-Seine, Haute- Vienne, Hérault, Indre, Indre-et-loire, Isère, Jura, Landes, Loire, Loire Atlantique, Lot, Lot-et-Garonne, Lozère, Maine-et-Loire, Mayenne, Nièvre, Paris, Puy-de-Dôme , Pyrénées-Atlantiques, Pyrénées-Orientales, Rhône, Saône-et-Loire, Savoie, Seine-et-Marne, Seine-St-Denis, Tarn, Tarn-et-Garonne, Val-de-Marne, Var, Vaucluse, Vendée , Vienne, Yvelines, Val-d’Oise, Meurthe-et-Moselle, Loiret, precise Public Health France.

Should we be worried though?

“We are heading towards an extension and multiplication of these episodes, the threat will only intensify in the future”, estimates Marie-Claire Paty, of the High Council for Public Health.

“We are not, in the future, safe from an epidemic”, adds SPF, which recalls the Italian precedent, in 2007 and 2017, on chikungunya.

Vigilance remains in order, while September “is a period conducive to the appearance of outbreaks”: “We are strongly mobilized”, indicates Public Health France, which recalls the classic prevention gestures, starting with emptying stagnant water cups. Knowing that research is underway to sterilize mosquitoes, and, “especially at the IRD in Montpellier, work on revegetation to fight against the heat while taking vector-borne diseases into account”.

Since dengue fever is often asymptomatic (in about 70% of cases), it can go largely unnoticed. Manifestations of the disease occur between 3 and 14 days after the mosquito bite, with an average of 4 to 7 days. The patient generally recovers spontaneously in a few days, but significant fatigue persists for several weeks.

Currently, there is no treatment for dengue fever. A vaccine exists, developed in 2015 by the Sanofi Pasteur laboratory, but it is only intended for people aged 9 to 45 living in endemic areas. To qualify, they must have been infected with the dengue virus for the first time.

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