The West Nile virus (which is rather called “virus du Nile Occidental” in French) is not rare: experts believe that it is the most widespread flavivirus on the surface of the planet, just after the dengue virus.
It is responsible for a disease, Nile fever (or “West Nile fever”, or “West Nile virus fever”), which is potentially serious.
West Nile virus (West Nile virus): who is it and how is it transmitted?
West Nile virus: identity card. West Nile virus belongs to the flavivirus family (flaviviridae), such as yellow fever, dengue, and tick-borne encephalitis viruses. It was first identified in 1937 in Uganda (in the West Nile region, hence its name) in a woman who suffered from a high fever.
West Nile virus: how is it transmitted? West Nile virus transmission to humans occurs in three stages. First, the virus develops in certain birds (passerines, raptors and aquatic birds are particularly at risk of being infected); two, a “vector” mosquito feeds on the infected bird (experts estimate that 75 species of mosquitoes are likely to carry the West Nile virus); thirdly, the mosquito comes to bite an individual, thus transmitting the virus to him.
Domestic animals (horses, in particular) can also be infected following a bite from a mosquito infected with the West Nile virus. More rarely, humans can be infected with the West Nile virus via a blood transfusion or an organ transplant. Human-to-human transmission is considered extremely rare by experts.
To know. In Europe, the West Nile virus was introduced by migrating birds from the African continent.
And also… In mainland France, this virus is regularly detected around the Mediterranean; in France, the main “vector” mosquitoes are Culex pipiens (which is present in all kinds of environments, including cities) and Culex modestus (which is confined to wetlands). These mosquitoes are particularly active between the beginning of June and the end of October, in the Mediterranean regions.
West Nile virus (West Nile virus): what are the symptoms of Nile fever?
Infection with the West Nile virus (West Nile virus) can cause the development of a viral disease: Nile fever. This zoonosis has been responsible for epidemics in Africa, Eastern Europe, the Middle East and Asia; it is emerging in Europe (in Germany, the Netherlands and France, in particular) and in the United States.
To know. In 2018, 27 cases of Nile fever were recorded in France, mainly in the Alpes-Maritimes department (06). 13 cases were also observed in horses. In 2019, the disease was identified in 2 people in the Var department (83).
Nile fever: what are the symptoms? In the majority of cases (80%), West Nile virus infection is asymptomatic: it goes completely unnoticed. On the other hand, in 20% of infected people, symptoms appear after 3 to 6 days of incubation:
- A high fever,
- headaches (headaches),
- Muscle pain (myalgia; especially back pain),
- cough,
- Swollen neck glands (adenopathy),
- A skin rash (on the trunk, in particular),
- Digestive symptoms (nausea, vomiting, diarrhea, etc.),
- Respiratory symptoms…
Rarely (in about 1% of the most severe cases), neurological complications may appear: this is called West Nile encephalitis or meningitis. This combines severe headaches with high fever, stiff neck, convulsions, tremors, paralysis…
To know. Specialists estimate that approximately 1 in 150 infected people will develop a serious form of the disease: this concerns in particular people aged over 50-55 and immunocompromised people. Nile fever is fatal in about 2% of cases.
Nile fever is a notifiable disease. Since May 12, 2021, West Nile virus infection has been a notifiable disease (MDO) in France.
This means that health professionals (doctors, biologists, etc.) are obliged to transmit medical data concerning a possible case of Nile fever to medical public health inspectors, to their collaborators in regional health agencies (ARS ) and epidemiologists from Public Health France. The objective: to monitor and prevent the risk of epidemics.
West Nile virus (West Nile virus): diagnosis and treatment of Nile fever
Diagnostic. There are several ways to diagnose West Nile virus infection. The virus or specific antibodies can thus be identified in the cerebrospinal fluid (CSF) or in the serum; there are also PCR tests for the West Nile virus.
Treatments. Unfortunately, at present, there is no vaccine for humans against Nile fever; however, there is a vaccine for horses. Treatment of West Nile virus infection is primarily symptomatic. In case of neurological symptoms, hospitalization is unavoidable.
Prevention. Prevention against the West Nile virus focuses on the fight against mosquitoes: it is a question of protecting oneself personally (with effective chemical repellents, mosquito nets, covering clothing, etc.) and protecting one’s environment (in particular by doing flushing stagnant water).
Sources:
- Public Health France
- Pastor Institute
- Ministry of Health
- Vidal Encyclopedia
- World Health Organization (WHO)
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- Why mosquitoes aren’t (only) attracted to your skin
- Dengue fever: a case in Ile-de-France, what is it, exactly?
- Tiger mosquito: size, bite, how to recognize it?
