‘West Nile’ virus has had three native French cases

Three native cases of the West Nile virus have been recorded in the Var department, sparking fears that the number of infections may begin to rise. 

The virus – originating in birds but which can spread to humans through mosquito bites – has been recorded in France before, but mostly in cases where a person has been infected abroad and then returned to the country. 

The French health authorities (Agence régionale de santé, ARS) state now that three cases have been caused by infected people being bitten in France. 

The bites are mostly spread by Culex mosquitoes.

Whilst it can often be asymptomatic, some cases result in lasting fevers and neurological damage and can be fatal in extreme cases.

What is the West Nile virus and where did it come from?

The West Nile virus was first recorded in Uganda in the 1930s, but cases have been recorded on all continents since then, it is particularly dangerous in parts of North America.

In Europe, it is endemic to parts of Greece and southern Italy, and other stretches of the Mediterranean. 

Cases have been present in France for decades, but were first recorded outside of the Mediterranean coast in 2023.

Read more: First case of mosquito-spread virus identified in south-west France

The virus primarily affects birds and mosquitos. Birds (mostly reservoir birds) host the virus, with mosquitoes feeding on them and becoming infected. 

They then pass the infection to other birds when they feed on them, resulting in a feedback loop between the two that rapidly increases cases.

However, humans and horses can become accidental hosts if bitten by an infected mosquito. 

Neither can transmit the virus to other members of their species, meaning they are ‘dead ends’ and the virus dies inside them.

In extremely rare cases, the virus can be passed on through blood transfusions or breast feeding, but cannot be transmitted outside of this contact via acts such as coughing or sexual contact. 

Read more: Dengue fever in France - how widespread is it in summer 2024?

How dangerous is the virus? 

In around 80% of cases, it is asymptomatic, with humans not knowing they have been infected. 

In the remaining 20% a high fever, known as West Nile Fever, occurs between three and six days after being bitten by a mosquito carrying the disease. 

This fever is accompanied by headaches and backaches, muscle pains, a cough, swollen neck glands. Often a skin rash, nausea, abdominal pains, diarrhoea and respiratory symptoms also present. 

Around 1% of cases result in neurological damage (such as meningitis). Other complications (hepatitis, pancreatitis or myocarditis) may occur, but this is less likely.

It is these which can lead to the death of a person infected with the disease.

The World Health Organisation estimates around one in every 150 people infected by the virus end up with a severe form of the illness.

Generally, anyone can be infected, but it is particularly dangerous for those over the age of 50, immunocompromised people, or who have had transplants or blood transfusions. 

Can it be treated? 

There is no general treatment against the West Nile virus, as it largely depends on the exact symptoms a person suffers. 

In general, those who suffer only a fever and other general pains begin to feel better after a few days, but some of the aches may linger as after-effects. 

Severe cases that result in hospitalisation are treated based on the symptoms patients present. 

The best way to reduce the number of cases is to combat the proliferation of mosquitoes; the ARS states. 

This includes removing potential breeding grounds from homes and using repellants (including sprays etc to prevent bites).