While cases of dengue fever imported into mainland France have already reached a record level in 2024, health authorities are on alert as this event approaches, which is expected to welcome more than 15 million tourists.
One month before the Paris Olympic Games, French health authorities have increased their level of vigilance towards dengue fever and other arboviruses (diseases caused by arboviruses). And for good reason: over the first six months of 2024, more than 2,800 imported cases were recorded in mainland France. This is more than the number of cases recorded over the whole of 2023, which was already a record compared to previous years.
Cases of dengue fever and other mosquito-related diseases are currently on the rise. “significant increase” in Europe, according to the European Center for Disease Prevention and Control, climate change favors the spread of tiger mosquitoes. The mosquito capable of transmitting dengue and other viruses – the tiger mosquito («Aedes albopictus») – was not present 20 years ago in mainland France. It has now spread to almost the entire territory, including Île-de-France.
Cases imported from the Antilles
Dengue fever is a viral disease that is most often benign, which can progress, in approximately 1% of cases, to a more serious form, notably causing bleeding. Deaths are very rare. Transmission of the virus occurs when a female tiger mosquito bites a contaminated carrier individual and on this occasion ingests viral particles. When she then bites another human, she will inject the virus at the same time as she sucks up her dose of blood.
Cases “imported” concern people who have traveled to regions of the world where the virus is circulating endemically. Since the beginning of May, a little more than half of the cases imported into mainland France returned from Guadeloupe or Martinique. The health authorities also alerted in mid-April about a situation “unpublished” in metropolitan France, linked to an outbreak of dengue fever in the Americas and the Caribbean, and called for increased vigilance, especially in the run-up to the Olympic Games, which are favorable to the mixing of populations. Around 15 million visitors are expected in Île-de-France during this period.
As of June 25, no episode of indigenous transmission of dengue fever by a mosquito present on site – but also of chikungunya or Zika – had yet been detected. In 2023, France had recorded around fifty indigenous cases of dengue fever, after a record of 66 in 2022.
Disinect within three weeks
Recently, researchers from the Pasteur Institute studied the ability of tiger mosquitoes to transmit five viruses (West Nile, chikungunya, Usutu, Zika and dengue), and determined the incubation time necessary for these viruses to be found in the glands. mosquito saliva in sufficient quantity to infect a human. They estimated that for dengue and Zika, this delay is between 14 and 21 days when the temperature is 28°C. “If a case of dengue fever is detected in Île-de-France, we now know that disinfestation must take place within 21 days. These results make it possible to adjust the window of opportunity so that the approach is optimal. “, declared in a press release Anna-Bella Failloux, head of the Arbovirus and insect vectors unit at the Pasteur Institute, who led this study.
In addition to arboviruses, the French Public Health agency has indicated that it will also maintain particular surveillance on food-borne infections, measles, but also on the risks linked to heat in the event of a heatwave.
