Should we be worried about West Nile virus?

A case of infection with the West Nile virus was reported on Tuesday August 1 in Gironde, signing an unprecedented occurrence of the virus outside the Mediterranean rim, according to information communicated by the regional health agency (ARS) in New Aquitaine. “Overnight, 2 new cases were confirmed. We are still awaiting confirmation from the national reference center for two other suspected cases which show biological signs in favor of a viral infection”, informs Dr Karim Tararbit, epidemiologist and expert medical adviser at ARS Nouvelle-Aquitaine. However, the regional agency wants to be reassuring because their state of health "does not inspire concern".

The symptoms of West Nile fever are relatively similar to those of the flu, including fever, joint and muscle pain, and headaches. In less than 1% of cases, there are neurological complications, especially in immunocompromised people. But most of the time, or 80% of cases, the infection does not cause symptoms in humans.

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Until 2010, the virus was mainly present in Africa, the Middle East and Western Asia, but since then a more active circulation has been observed in Europe. Between 2019 and 2020, Germany and the Netherlands reported their first cases. As far as France is concerned, only the Paca and Occitanie regions have so far been concerned, with cases regularly recorded over the past two decades in humans and horses. “Recently, 17 human infections were reported in the Alpes Maritimes in 2018, 2 in the Paca region in 2019, 6 in 2022”, reports Dr Tararbit. “So it remains a rare but well-known infection in France,” he insists. Nevertheless, this new appearance of the pathogen in Gironde raises concerns about its potential spread to other regions of France.

Birds are the main reservoirs of the virus which was discovered in Uganda in 1937. With climate change, the more favorable climate for migrating birds from Africa remains one of the probable hypotheses as to the introduction of the virus into Europe. Transmission to humans occurs through mosquitoes of the Culex genus, the most common in France. By biting infected birds, these mosquitoes now carrying the virus are likely to transmit it to other birds, humans being considered as “an accidental host”. However, this virus would not be transmissible between humans, nor from humans to mosquitoes. “These factors limit a more massive spread but the viruses evolve regularly so nothing is certain. “, underlines Dr. Tararbit.

Although the threat is currently low, health authorities remain cautious. An investigation under the direction of ARS Nouvelle Aquitaine and the national health agency, Santé Publique France, has just been launched with the aim of documenting the sources of contamination and estimating the area of ​​​​spread of the virus. Ultimately, this will make it possible to take all appropriate measures to limit its extension to other areas. “In particular, we have launched an alert with the French Blood Establishment because there is a risk, even if it is very low, of transmission through blood or organ donations. Security measures have already been put in place since July 28, when the first suspicions arose,” says Dr. Karim Tararbit.