Dengue fever: increase in France, symptoms, is it serious?

[Mise à jour le 16 septembre 2022 à 09h52] the risk of dengue fever in France (mainland) increasesinform the General Directorate of Health in a letter dated September 12. Since July 2022, 26 indigenous casescorresponding to 5 episodes of transmission of which 3 major foci were identified in the PACA and Occitanie regions. Cases have occurred in departments hitherto spared, such as Eastern Pyrenees (66), Haute-Garonne (31) and Hautes-Pyrénées (65)and clusters of cases have also been confirmed in Alpes-Maritimes and the Var. “Other cases or outbreaks are likely in the coming weeks in mainland France.“ warns the DGS. The risk of dengue cases is highest from May to November. According Public Health Francefrom 1^er May to September 2, 2022, 139 cases imported dengue fever have been identified in France including 133 in departments with documented establishment ofAedes albopictusthe famous tiger mosquito (67 in all). the dengue fever report, as well as chikungunya and Zika, is obligatory. What are the symptoms of dengue fever? When to consult? Are there treatments? What are the risks in case of bites ?

“In recent years, Aedes albopictus, vector of dengue fever in Asia, has established itself in North America and Europe, including France where 2 first autochthonous cases were identified in 2010 in Nice“ informs Professor Anna-Bella Failloux, head of the “Arboviruses and Insect vectors” research and expertise unit at the Institut Pasteur. According Public Health Francefrom 1^er May to September 2, 2022, 139 cases imported dengue fever have been identified in France including 133 in departments with documented establishment ofAedes albopictusthe famous tiger mosquito. These cases are mainly recorded in the south of France, in the Occitanie and Paca regions. The risk of dengue cases is highest from May to November.

List of departments with documented implementation ofAedes albopictus at 1^er May 2022

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.

Dengue is a disease caused by a virus transmitted to humans by female mosquitoes of the genus Aedesmainly the species Aedes aegypti. Aedes albopictus, more commonly known as the tiger mosquito can also transmit dengue. It is a very often mild disease. Dengue virus is a arbovirus (virus transmitted by insects) divided into 4 serotypes :

• DEN-1,
• DEN-2,
• DEN-3
• DEN-4.

In people who have been infected, recovery leads to lifelong immunity against the serotype causing the infection, but not against the other three. An individual can therefore be infected with each of the four dengue serotypes during their lifetime.

The vector of the dengue virus is the Aedes aegypti mosquito and the tiger mosquito which live in urban areas and breed mainly in containers with standing water. In Aedes aegypti, cis the female that stings, mainly during the day, with a peak of activity in the early morning and evening before dusk. “Aedes albopictusat daytime activity, present in Asia, has spread to North America and Europe. Endowed with great ease of adaptation in temperate zones, it was introduced in 2004 in the Alpes-Maritimes, and its area of ​​implantation continues to expand”recalls Professor Anna-Bella Failloux, head of the “Arboviruses and Insect Vectors” research and expertise unit at the Institut Pasteur.

A person infected with dengue is not contagious to another human being.

► The mode of contamination is classic : the mosquito becomes infected by biting an already infected person and can thus transmit the virus by biting another individual a few days later. Once in the body, the virus multiplies and persists for 3 to 10 days. The person infected with dengue fever is not contagious for another human being, on the other hand it can contaminate other mosquitoes of the genus Aedes if it is bitten again in a period ranging from 1 to 2 days before the onset of symptoms and up to 7 days later. The virus can, more rarely, be transmitted by transfusion or transplantation (of organs or cells).

The dengue fever is asymptomatic in 50 to 90% of cases (variable percentage according to the epidemics). Symptoms are most often flu-like (sudden high fever, headache, nausea, vomiting, joint and muscle pain, and rash resembling that of measles) manifesting within 3 to 14 days (4 to 7 days on average incubation period) following the mosquito bite. The acute phase lasts about a week. Most often benign although debilitating, classic dengue can however be complicated by hemorrhagic forms. A critical phase can occur between the 4th and 6th day about ; them warning signs are a fever >39°C after the 5th day, severe abdominal pain with or without diarrheaof the uncontrollable vomitingrestlessness or drowsiness, edema, hemorrhagic signs.

The incubation period of dengue fever ranges from 3 to 14 days: 4 to 7 days on average.

Dengue affects infants, young children and adults alike. So there are no people at risk more than others. Nevertheless, people living in areas with high circulation of the virus (see below) are most at risk.

Two and a half billion people live in areas at risk. Dengue is rampant mainly in the whole intertropical zone. Long limited to Southeast Asia, it continues to extend to the Indian Ocean, the South Pacific, the West Indies French andLatin Americawhere reported annual cases increased 60-fold between 1989 and 1993 compared to the previous period (1984-1988).

Nonsteroidal anti-inflammatory drugs and aspirin are contraindicated.

Early diagnosis can be made by search for NS1 antigen, a dengue virus protein detected in the serum of people with dengue at the onset of fever; the identification of the virus can also be carried out early.
The search for IgM-type antibodies, only becomes positive around the 6th or 7th day of fever and persists for an average of 2 to 3 months. Other more sophisticated biological examinations, such as PCR or viral cultures, are reserved for research or the very specialized laboratories of reference centres. “The biological diagnosis allows the declaration of the disease; on the other hand, if we accept the theory according to which a second infection could be more severeit is preferable for a person to know whether or not they have already had an episode of dengue fever, in order to adopt even more drastic preventive measures”says Professor Failloux.

The diagnostic approach recommended in the ministerial plan “anti-dissemination of chikungunya and dengue fever” is as follows:

• Up to 5 days after the onset of signs (D5): RT-PCR
• Between D5 and D7: RT-PCR and serology
• After D7: serology only (IgG and IgM) with a second confirmation sample at the earliest 10 days after the first sample

Blood samples can be taken by any analysis and medical biology laboratory.

There is no no specific treatment dengue. The treatment is symptomatic, intended to fight against pain and fever. Nonsteroidal anti-inflammatory drugs (ibruprofen, etc.) and especially aspirin are contraindicated due to thrombocytopenia (low platelet count) and hemorrhagic risk.

There is no vaccine against dengue fever. Prevention therefore relies on effective vector control measures.

According to the ARS, to avoid mosquito bites, it is advisable to:

• wear covering and ample clothing, even to impregnate them with insecticide for fabrics;
• use a skin repellent, preferably in the morning and evening, recommended by a pharmacist, on exposed areas of skin;
• if necessary, use mosquito nets on the openings (doors and windows);
• using crib nets for newborns;
• use electric diffusers inside homes;
• use insecticide coils only outdoors;
• use air conditioners or fans that interfere with mosquitoes.

To limit the development of mosquitoes around your homeit is right to :

• empty, store or dispose of any container that may contain water;
• cover water supplies with a mosquito net or cloth to make them airtight;
• clean gutters and gutters;
• avoid illegal dumping of waste.

Dengue virus infection during pregnancy does not cause no increased risk of disease or worsening disease in the mother. The rate of malformations is not increased, but occasionally cases of congenital dengue fever are observed. Premature births and abortions are possibly more common in dengue patients. Infection of the fetus occurs before birth, during the last weeks of pregnancy.

Clinical vigilance should be maximal around the 4th day.

In children under 15 years old, hypovolemic shock may set in (cooling, clammy skin and imperceptible pulse signaling circulatory failure) and lead to abdominal pain. Appropriate medical treatment is necessary to avoid complications and the risk of death. An intravenous infusion must be started quickly to restore the blood volume because haemorrhages can lead to significant blood loss.

Severe dengue is a life-threatening complication by the occurrence of a State of shock or bleeding complications. Generally after the resurgence of fever, the infection starts again and can evolve in rare cases (1% of cases in people with dengue symptoms) to severe dengue. Clinical vigilance should be maximal around the 4th day. The dengue usually heals within 2 weeks, but recovery time may take several weeks. Patients may feel quite tired during this period and develop depressive symptoms.

Produced with Professor Anna-Bella Failloux, head of the “Arboviruses and Insect vectors” research and expertise unit at the Institut Pasteur.