Mosquito-borne diseases spreading in France

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Mosquito-borne diseases spreading in France
This image shows Culex quinquefasciatus, a representative of the Culex genus of mosquitoes. (AFP PHOTO/JIM GATHANY/CENTER FOR DISEASE CONTROL AND PREVENTION)

For the first time, France has recorded several cases of locally-acquired mosquito-borne infections, such as West Nile virus, as experts warn that rising temperatures could increase the presence of virus-carrying mosquitoes in other parts of the country.


As of early September, there had been eight probable or confirmed cases of native West Nile virus contracted in France, as well as four cases of the Usutu virus in south-west France.

The summer of 2023 marked the first time the West Nile virus was contracted in a part of France outside of the country's Mediterranean coast, and in particular the first time people became infected in the south-west of France.

Experts believe that France will start to record more mosquito-borne infections, in part thanks to improved detection methods and warming temperatures as a result of the climate crisis.

Mosquito specialist Anna-Bella Failloux told Franceinfo that the country's detection system for mosquito-borne illnesses "is becoming increasingly precise and refined, which explains why more and more cases of contamination are being reported".

"That does not necessarily mean that there are more, but we can be certain that changes in climate and human activity are contributing to a population explosion in mosquitoes and therefore the transmission of viruses they can carry," Failloux said.

Rising temperatures across France also have a physical impact on mosquitoes' ability to spread disease. The heat can cause viruses to "multiply more rapidly in their metabolic system, meaning they reach salivary glands much more quickly".


Both the West Nile and Usutu viruses are carried by the Culex mosquito - not to be confused with the Tiger Mosquito which is present across much of French territory and is known for being able to carry illnesses such as Zika and Dengue.

As of September 2023, France had not seen any native cases of Dengue fever, but there had been several cases recorded among people who had recently travelled from countries where the disease is endemic. 

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The Culex mosquito had previously only been present along the Mediterranean, but now experts say that it has begun to spread toward the Atlantic coast as well, reaching the Nouvelle-Aquitaine region. 

France has carried out several mosquito-control campaigns, which involves spraying pesticides in an area where the infected insects likely inhabit. However, Failloux warned that while these operations are essential to contain possible epidemics from arising, "only one insecticide molecule is authorised, so as with antibiotics in humans, mosquitoes can develop resistance to it.

"This means that doses must be increased to be effective, which can have harmful impact on the environment," she told Franceinfo.

When it comes to infection from the West Nile virus, France has only ever recorded cases along its Mediterranean coast, namely in the regions of Provence-Alpes-Côte d'Azur and Occitanie. In 2018, at least 30 people in Alpes-Maritimes were infected, with some requiring hospitalisation. 


The Usutu virus, which is thought to have been in circulation in mosquitoes in France since 2015, with very few cases having been recorded since. One took place in 2016 near Marseille, and French regional health authorities said that they believed to have identified another in the south-west of France in November 2022.

In terms of danger to humans, West Nile virus generally causes flu-like symptoms, but in some people it be life-threatening, particularly by causing neurological disorders like encephalitis or meningoencephalitis. There is no vaccine currently available. 

In contrast, French health authorities have described the Usutu virus as "not presenting a real danger to humans."

"However, very rarely and in immunocompromised people, it can cause neurological disorders," French health authorities said in a statement.



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