Dengue fever, a disease transmitted by the tiger mosquito, is spreading to a degree never seen in mainland France. Although there are still only a few dozen cases, this rise illustrates how much climate change affects public health.
Where does the disease strike?
Dengue fever is currently a tropical disease. Overseas, certain French regions (Guadeloupe, Martinique, Réunion, etc.) are regularly hit by major epidemics.
The novelty of recent years is the arrival of dengue fever in mainland France. Since the 2010s, a few “indigenous” cases (which do not come from contamination outside the territory) have been reported each year. This trend has taken a new step this summer. In mid-September, the health authorities identified around forty cases, concentrated in the South, a figure destined to increase further this year.
Afterwards, “we are moving towards an extension and multiplication of these episodes”warned epidemiologist Marie-Claire Paty, during a conference of Public Health France, this Friday, September 16. “We are not immune to epidemics in the future” in mainland France, she insisted, admitting that their magnitude would certainly be less than overseas.
This progression of the disease stems from its mode of transmission.
How does dengue fever circulate?
Dengue needs an intermediary: mosquitoes. After biting a patient, they may find themselves carrying the virus and transmitting it to their future victims.
This is also the case with malaria, which is transmitted by Anopheles mosquitoes, while dengue fever spreads via several species of the “Aedes” genus. There is notably the tiger mosquito, whose presence was limited a few decades ago to Southeast Asia but which is now establishing itself in Europe and America.
In metropolitan France, this species, absent before the 2000s, has gained two thirds of the territory.
This does not mean that dengue fever cases are so prevalent. But their spread tends to follow, with a lag of a few years, the establishment of the tiger mosquito. A phenomenon observed in other countries with similar diseases. Italy, one of the first European countries to have seen the arrival of this insect, has thus recorded in recent years hundreds of cases of chikungunya, another virus transmitted by this mosquito.
Why this progress?
The spread of the tiger mosquito is “favoured by the globalization of trade and travel, the advance of urbanization and climate change”summarized in 2014 the World Health Organization (WHO).
The insect lives in fact only in the city, prefers humidity and heat, can slip into luggage or imported products.
The fight against this mosquito, and beyond against dengue fever, resonates particularly with a concept in full swing in public health: “One Health (one health)”, insisting on the interdependence between human health, animal health and protection of the environment.
How to fight dengue?
There is a vaccine, produced by the Sanofi laboratory, but its effectiveness is too insufficient to recommend it to people who have never caught dengue fever.
The fight against the disease begins with the environment, starting with mosquitoes spreading the virus. The “mosquito control” operations thus aim to identify and destroy the centers of larvae. But this can come up against other measures against the effects of climate change, such as planting plants to reduce the accumulation of heat in the city.
“There may be water collection and breeding sites”warned Ms. Paty, however, judging it possible to reconcile the two issues.
Still, once installed somewhere, the tiger mosquito cannot generally be completely eradicated. In the long term, the solution would rather be to instrumentalize it.
Several approaches exist. One of the most promising consists of introducing mosquitoes infected with a bacterium that blocks the circulation of the virus into the wild.
Several studies, the most important of which was published last year in the New England Journal of Medicine, suggest that this approach, particularly practiced in New Caledonia, significantly reduces cases of dengue fever.