None of these two cases has traveled in the endemic zone. The first case, identified at the end of July, also stayed in the Jura department (Burgundy-Franche-Comté) during the possible period of risk exposure. The second case, confirmed on August 6, did not leave Île-de-France within 15 days of the appearance of symptoms. These are the first identifications of local vector transmission of the West Nile virus in Île-de-France.
Transmission modes and symptoms
The Western Nile Virus is transmitted to humans mainly by the bite of a mosquito of the genre Culexinfected after having stung a bird carrying the virus. This mosquito, common in France, spikes especially in the evening and at night, unlike the tiger mosquito, Aedes Albopictus, active during the day.
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No direct transmission between humans, nor via a mosquito having bitten an infected person.
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Seasonal transmission: from May to November, period of activity of vectors mosquitoes.
In 80 % of cases, the infection is asymptomatic. When it is symptomatic, it manifests itself by a pseudo-grippal syndrome (large fever accompanied by headaches, muscle or abdominal pain, nausea, diarrhea).
In rare cases (less than 1 %), neurological complications (meningitis, encephalitis) may occur. Generally, the patient spontaneously recovers, sometimes with sequelae. But viral infection can be fatal mainly in the elderly.
Since 2021, the fever of the Western Nile Virus has been registered on the List of Mandatory Declaration Diseases (MDO).
One case is defined as indigenous when no trip to the endemic zone took place within 15 days preceding the symptoms. As soon as a proven case of arbovirosis is reported at ARS, a health survey is conducted by the agency and public health France to identify any recent displacement of the contaminated person in endemic zone or contact with a sick person.
Surveillance and prevention system
Present on several continents, the Western Nile Virus has known, since 2010, a progressive extension in Europe, especially in the countries of the South, with an increase in neuro-invasive forms.
In France, a tripartite surveillance system in humans, horses and birds exists. It is based on the sectors of human health (ARS, Public Health France, National Reference Center for Arboviruses, Health Professionals) and Animal Health (Equine and Avian – ANSES, National Reference Laboratories, National Biodiversity Office), as well as the Departmental Directions for Population Protection (DDPP), research teams, demonstrators of demoustication and entomologists.
This surveillance is reinforced each year from May 1 to November 30, period of activity of vectors mosquitoes. It aims to quickly detect the circulation of the virus to trigger protective measures, in particular the security of blood and organ donations.
Actions implemented by ARS Île-de-France in collaboration with other actors
Faced with an unprecedented situation in Île-de-France, ARS intensifies its cooperation with several partners in order to characterize the health risk, limit its extension and ensure a coordinated response on the impacted territory:
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Epidemiological survey in collaboration with the regional public health unit France to identify possible places of contamination;
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Temporary security of products from the human body as soon as the alert concerning labile blood products but also the donations of organs, tissues, cells and gametes by the French Blood Establishment (EFS) and the Biomedicine Agency (ABM), in connection with Public Health France;
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Awareness of Ile -de -France health establishments likely to accommodate people with serious forms of the disease;
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Strengthening entomological surveillance around confirmed human cases and potential areas of avian transmission;
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Mobilization of animal health actors to strengthen surveillance in birds and equines present in Île-de-France.
Recommendations for the general public
1- Protect yourself from bites in the event of a mosquito presence:
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Wear covering and loose clothes, especially in the evening, mosquitoes Culex mainly having a night activity;
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Use suitable repellents, advised by a pharmacist, on discovered skin areas;
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Install mosquito nets or fences at the doors and windows;
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Use indoor electric diffusers and insecticide serpentine only outside.
2 – Consult a doctor quickly in case of evocative symptoms: Brutal appearance of significant fever accompanied by head and back pain, muscle pain, cough, swelling of neck nodes, and often rash, nausea, abdominal pain, diarrhea and respiratory symptoms.
