Nile virus: 5 cases in the South West, is it fatal?

The Nouvelle-Aquitaine Regional Health Agency has received the report of the first autochthonous human case of West-Nile virus infection in a person residing in Bordeaux (Gare district) on July 27, 2023, can we read in a press release from the ARS of August 1, 2023. 4 other cases have been reported in Gironde and are under investigation, jointly with Public Health France. Nevertheless, “their state of health does not inspire concern and they are in the process of recovery“. These 5 cases represent the first human cases whose infection was acquired in New Aquitaine. So far, in France, human infections with the West-Nile virus have only been found around the Mediterranean (PACA and Occitanie regions).

What is West Nile Virus?

West Nile Virus West Nile Virus) is a arbovirus of the genus Flavivirus (Flaviviridae family). It is considered today as the Flavivirus most common after dengue fever. It was first isolated in 1937 in the West Nile district of Uganda (Africa)hence its name, recalls Public Health France. It has historically been responsible for epidemics in Africa, the Middle East, West Asia and Europe. It appeared in North America for the first time in 1999 and in a few years it spread throughout the territory. In France, it is regularly detected around the Mediterranean. “It is transmitted to humans by mosquitoes, and more particularly by Culex Mosquito“, continues Dr. Pascal Del Giudice, infectiologist, and specialist in pathology. In Europe the virus was initially introduced by migratory birds from Africa. “The main hosts of the virus are birdsmammals (like man) are accidental hosts“.

What Symptoms Cause Nile Virus?

“In 80% of cases, West Nile virus infection does not cause symptoms“, continues the specialist. The symptomatic forms of the disease are characterized by: sudden and significant fever after 3 to 6 days incubation, which can be associated with a rash (discreet red patches). “THE serious forms of the disease are rare (less than 1% of cases) and mainly affect adults and in particular the elderly. These are neurological disorders which manifest themselves by meningitis, encephalitis, meningoencephalitis… Moreover, in the south of France, where mosquitoes are very present, any syndrome with a neurological disorder and a high fever during the summer period, is the subject of a test for the detection of the Nile virus.“.

What is the mortality from West Nile Virus?

In cases of severe forms, where the disease presents as a severe neurological form (aseptic meningitis, meningoencephalitis, acute flaccid paralysis, Guillain Barré syndrome) mainly described in weakened subjects, the lethality was evaluated at 2% of infectionsreports the Ministry of Health.

Is the Nile Virus present in France?

Since its first identification in East Africa, the virus has been identified on all continents, underlines the Pasteur Institute. Today it is endemic around the Mediterraneanin Central Europe and North America where it is responsible for fatal human cases as it has been observed in mainland Greece, southern Italy and the United States. The year 2018 was marked by the largest epidemic described, the number of cases recorded in Europe was higher than the sum of the previous 7 years, notes Public Health France. In 2019 and 2020 human cases were reported for the first time in Germany (2019 and 2020) and the Netherlands (2020). In France, the first human and equine cases have been diagnosed in the early 1960s. The virus reappeared in horses in the Camargue in 2000, and 7 human cases were identified in 2003 in the Var and one case was reported in New Aquitaine in 2023.. “The virus travels with migratory birdscontinues our interlocutor. The number of cases therefore varies each year.

The diagnosis can be confirmed by biological analyzes carried out in the blood and/or in the cerebrospinal fluid (CSF)through a lumbar puncture.

Frequent infections in horses?

“The horse is a species that is particularly susceptible to the West Nile virus. The viral infection is characterized by fever, encephalomyelitis and paralysis of the hind limbs, and causes a significant mortality rate. Cases of horses infected with the West Nile virus have been reported in several countries in Europe and the Mediterranean basin: in Egypt, in Italy (1998), in Israel (2000), in the United States (1999-2004), in France (in the Camargue in 2000 and in the Eastern Pyrenees in 2006), in Guadeloupe in 2002, and in Morocco in 2003, 2010, recalls thePastor Institute.

“Those are the Migrator birds which act as reservoir animals for the West Nile virusexplains Dr. Del Giudice. Transmission of the virus to humans then occurs through bite of a mosquito, of the genus Culex. Mosquitoes become infected by feeding on infected birds“. Just like man, horses are also susceptible to infection. “The only vector of contamination being the mosquito, the disease is only present in the summer period, between June and October.“.

What is the treatment for West Nile Virus?

“To date, there is no no specific antiviral treatment against the West Nile virus, concludes the doctor. Only the symptoms are treated: for example, by giving paracetamol to lower fever“. For the horse, a equine vaccine is marketed. Prevention of West Nile virus infection is limited to protection measures against mosquitoes (individual and collective)

Mosquitoes Culex mainly bite at sunset and at night, outdoors and in homes.

According to ARS Nouvelle Aquitaine, the most effective preventive measures to protect against mosquito bites are:

• wear covering and loose clothing;
• use a skin repellent in the evening, recommended by your pharmacist, on uncovered areas of skin;
• if necessary, use mosquito nets on the openings (doors and windows);
• sleep under mosquito nets, which may also be impregnated with fabric insecticide. There are crib nets for newborns;
• use fans and possibly air conditioners that bother mosquitoes;
• use electric diffusers inside homes;
• use insecticide coils only outdoors;

To limit the development mosquitoes around your home, you should:

• cover water supplies with mosquito nets or fabric to make them airtight;
• clean gutters and gutters;
• empty or store any container that may contain water (tip: fill the cups with sand);
• avoid illegal dumping of waste.

Thanks to Dr Pascal Del Giudice, head of the infectiology and dermatology department of the hospital center of Fréjus-Saint-Raphaël.