Rising Cases of Dengue Fever in Mainland France: Causes, Prevention, and Outlook for the Future

2023-10-04 16:05:53

Specialists in infectious and tropical diseases note more cases of dengue every year in mainland France, particularly in the departments along the Mediterranean coast. Indigenous cases are closely monitored to prevent the virus from becoming endemic.

Usually absent from mainland France, dengue fever has been an infectious disease requiring notification since 2006. Each reported case, whether imported or indigenous, leads to a health investigation.

In 2022 alone, 66 cases of indigenous transmission of dengue were identified in mainland France, including 52 in PACA and 12 in Occitanie, Gard and the Pyrénées-Orientales. And 378 imported cases were reported compared to 48 cases in 20 years, between 2001 and 2021.

For 2023, 18 indigenous cases are recorded in Occitania for the period from May to mid-September. Every year, there are more and more cases, especially indigenous ones. Climate change and rising temperatures around the Mediterranean have a lot to do with it. And specialists predict an almost inevitable increase in cases of dengue, chikungunya and Zika in the years to come.

The increase in cases and particularly indigenous cases is due to the increase in the population of mosquitoes which are the vectors of infection. Research and systematic reporting of cases also play a role.

Charlotte Boullé, infectious disease specialist in the infectious and tropical diseases department of Montpellier University Hospital

For the infectious disease specialist, local cases are linked to imported cases. “For a person who has not stayed in a risk area to be infected, they must have been bitten by a contaminated mosquito, therefore must have first bitten a person carrying the virus, native or imported, nearby, because the mosquito does not move within a radius of more than 100 to 300 meters.”

Hence the importance for travelers returning from the Caribbean, Guyana and Reunion, symptomatic or not of the disease, to protect themselves from mosquito bites for 15 days following their return, to avoid transmission of the virus.

Our fear is that with the progression of the establishment of the tiger mosquito in mainland France, dengue fever will become an endemic disease.

Charlotte Boullé

In France, there is a vaccine once morest dengue but its use is rare.

There are actually four genera or serotypes of dengue. The vaccine can be effective once morest a first contamination with one of the serotypes but several studies show that in the event of a new infection with a serotype different from the first, the risks of developing a serious form are greater.

As of January 1, 2023, the tiger mosquito was present in 71 departments of mainland France out of a total of 96. • © Ministry of Health.

After the reporting of two indigenous cases of dengue fever in the Gard, in Rochefort-du-Gard and Gagnières, on September 19, a door-to-door investigation was carried out. Teams from ARS Occitanie and Public Health France interviewed concerned residents, which made it possible to identify five new cases of dengue fever on September 22. Their state of health does not cause concern.

Other suspicious cases, noted during these investigations, are still under investigation.

A first mosquito control operation was therefore carried out on the night of September 22, by the company Altopictus, at the request of ARS Occitanie. Faced with these cases grouped in a small geographical area, the targeted mosquito control operation was renewed twice (on September 25 and 28).

These operations aim to destroy all mosquitoes established near the living areas of infected people, to eliminate possibly contaminated tiger mosquitoes, following having bitten one of the sick people.

Mosquito control operation in urban areas once morest the tiger mosquito – archives. • © FREDERIC CHARMEUX / MAXPPP

All residents of affected areas who present clinical signs suggestive of a dengue infection are urged to consult their doctor promptly.

The suggestive symptoms are, in the absence of another established diagnosis:

a high fever (>38.5°C) of sudden onset associated with at least one other clinical sign such as headache, muscle or joint or lower back pain in the absence of cough, runny nose, sore throat , difficulty breathing or infected wounds.
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