2023-09-17 07:00:00
Fever, muscle pain, vomiting, bleeding… Between August 21 and September 3, the French Public Health agency recorded an outbreak of dengue cases in the French Antilles archipelago. Worrying thresholds had already been reached at the beginning of July but, in recent days, 770 significant clinical cases have been recorded in Martinique and 600 in Guadeloupe. Twelve of the patients died from bleeding complications. The epidemic phase is declared.
The authorities have logically relaunched a campaign to remind people of useful actions such as wearing long clothes, using repellents on the entire body and systematically emptying stagnant water. But in reality, the inhabitants of these islands have learned to live with the threat of dengue. This virus, which is transmitted only by mosquito bites, has been present there for more than 50 years (14,000 contaminations in 1977). On the other hand, recent decades have seen a clear acceleration of the disease: “20 years ago, the Antilles experienced epidemic peaks every 4 or 5 years,” explains Didier Fontenille, research director at the Research Institute for development (IRD). Now, there are years where dengue is weak, others where it is strong but the threat has become constant. »
READ ALSO Zika, dengue, West Nile… These exotic viruses that threaten us
This worsening of the situation is based on several factors, starting with the different strains of dengue (there are four) which develop alternately. “Contaminated populations are immune to a certain type of dengue but they become vulnerable again when another form develops,” summarizes the entomologist.
The other reason is linked to the climate which favors and accelerates the reproduction of mosquitoes carrying the virus. Epidemics are thus traditionally linked to the El Niño meteorological phenomenon, responsible for rainy episodes and heat conducive to the proliferation of the insect. In the current context, this is an additional source of concern since El Niño has officially returned after several years of absence. Its effects are only just beginning to be felt.
READ ALSO Why you attract (or not) mosquitoes
An imported disease
In mainland France, dengue fever has long been considered an exotic disease, a bad memory brought back from a stay in the tropics. But this perspective changed radically with the invasion of l’aedes albopictus, the tiger mosquito, now present in all departments. It turns out to be a close cousin of the West Indian mosquito, the Aedes of Egypt, and that they are both very effective vectors of dengue fever: “Of the 3,700 species of mosquitoes listed in the world, only 20 are capable of transmitting the virus,” explains Didier Fontenille. Bad luck, those we meet are on the list.
We then understand the link that unites France and the Antilles in the face of the problem. A traveler can very well be infected in Guadeloupe, return during the incubation period which can last 7 days and report symptoms once arrived. All it takes is for a tiger mosquito to bite it to then spread the virus.
With 3,000 passengers leaving Martinique every day and more than 5,000 leaving Guadeloupe, this scenario is not only likely, it is recurring and the peak episodes match between the two regions of the globe. “Between May 1 and September 8, 675 cases of dengue fever were imported into mainland France, mainly from the Antilles but also from Thailand, Mexico and Guyana where the virus is also very present,” observes the research director. of the IRD.
READ ALSO Is the invasion of the tiger mosquito due to climate change?
Stemming indigenous cases
Fatally, these contaminations led to indigenous cases of dengue fever. Public Health France counted 65 in 2022 and several outbreaks were again identified this summer. If only a few dozen people have been contaminated in the metropolis, it is because dengue fever is the subject of close surveillance by the health authorities and their response is relentless.
The latest example, this September 14 in the early morning, the town of Sainte-Foy-lès-Lyon, in the Rhône, was invaded by men in white overalls urgently dispatched to carry out mosquito control over several blocks. The reason: a single case of dengue fever identified in a traveler who had recently returned from a contaminated area. The same scene occurred in the Nantes suburbs a few days earlier, as well as in Colombes (Hauts-de-Seine) and Paris, at the end of August, for the same reason.
READ ALSO “Man is the tiger mosquito’s favorite animal”
Soon a vaccine?
Today, the fight against the tiger mosquito (and all its cousins that carry dengue) constitutes, along with prevention, the only levers in the fight against the virus because there is no remedy to protect against it. But how can we defeat an enemy that happily profits from excessive urbanization and the effects of climate change? Repeated heat waves, increasingly mild winters and torrential rains are all factors in the development of the “tiger” and therefore dengue fever in mainland France.
Among the solutions that are emerging, the most effective is quite paradoxical: introducing even more mosquitoes. Didier Fontenille explains: “I am working with my teams on a new technique called the sterile insect. This involves releasing sterilized males who will produce empty eggs in order to limit the proliferation of individuals and therefore potential carriers of diseases. It is above all a preventive tool but the first tests carried out on Reunion Island were rather conclusive. »
Finally, another reason for hope lies in the development of a vaccine against dengue fever, in particular the Japanese “Takeda” which has started its marketing in certain regions but not yet on a large scale. There is no doubt that the waiting list is long. Today the virus is present in 129 countries.
#dengue #virus #arrives #France