The tiger mosquito continues its meteoric rise in France

Summer is the best season for the tiger mosquito. Its density increases until September. One in two French people could be bitten this year by the tiger mosquito, at home or at their vacation spot. This estimate is on the rise. We are going to experience a serious public health problem.” ​Director of research at the Institute of Research for Development (IRD), Didier Fontenille directs the Infectious Risks and Vectors program in Montpellier. The tiger mosquito (Aedes albopictus) can transmit dengue, Zika and chikungunya viruses. To better understand this health nuisance, 120 researchers and international public health actors met in congress at the IRD the last month.

Insect control operations from La Rochelle to Strasbourg

Originally from the forests of Southeast Asia, the mosquito has colonized temperate zones for 40 years. In Europe, it bites in more than 20 countries. Reported in France in 2004 in Menton (Alpes-Maritimes), it now colonizes 67 departments. Mathematical models predicted its expansion, but we were surprised by this speed”. On the website of the Ministry of Health, the presence map in France of the tiger mosquito shows a meteoric rise. From La Rochelle to Strasbourg, the Regional Health Agencies are carrying out insect control operations.

To the West, present from Vendée to Mayenne, it progress in Loire-Atlantique “where it should become abundant” notes the medical entomologist. The mosquito net is also detected in Brittany where the Regional Health Agency is now strengthening surveillance.

Colonization by roads

Easily recognizable by its color, black and white tabby, Aedes albopictusis original, compared to the 65 other mosquito species in France, 15 of which bite humans. Not only because it stings during the day, instead of waiting for the night. Its very wide genetic variety is quite astonishing. This is one of the reasons why it adapts to very different environments”.

Climate change is not the primary cause of its spread: its colonization follows the highways and main roads. A female enters a car, she comes out further and her eggs colonize another region”. The recent heat wave did not favor the insect: a study in a mosquito farm showed high mortality above 31 degrees.

Mosquito bites can cause allergic reactions. It is already a nuisance, believes Didier Fontenille, who cites the testimony of people “bitten ten times a day near Montpellier, in Nice, Marseille, and Toulon. It is the main mosquito in town, in the south of France”.

It is the potential transmission of viruses that worries specialists. It is very low today: only 82 people have been bitten in France, in ten years, by a tiger mosquito carrying dengue fever, but also Zika and chikungunya. These “indigenous cases” were contaminated by a mosquito, which had bitten a sick person a few days before, returning from a tropical region where dengue is rife. The number of dengue cases will increase in France, it is inevitable, ​estimates the entomologist, especially since travel has resumed. We expect ten or twenty autochthonous cases this year”.

​Hundreds of “imported” dengue cases are also identified each year in France. They are travelers from Overseas, from Reunion where dengue fever has been circulating since 2018 to Polynesia.

Release sterile mosquitoes

How can this nuisance be reduced? The tiger mosquito thrives in small water reserves: the saucer under the flowers, children’s toys left in a garden, a badly cleaned gutter. A first solution, already encouraged in communities in Occitania, consists of emptying all these containers where the water is stagnant.

Several types of traps exist, not always effective, as a study by ANSES has shown. Researchers the receptors, studying the behavior of mosquitoes. Another strategy is to release millions of X-ray-sterilized male insects into the wild. Drones transport cups of sterile males, dropped at sensible places. They will mate with wild females whose eggs will not hatch.”

This method was used in Reunion, as part of a project associated with IRD and ARS: 300,000 sterile males released each week reduced mosquito populations by half in a control area. Other scientists are looking for insecticides of biological origin: viruses that only kill these mosquitoes.

Everyone can participate in the fight against this mosquito. The ANSES signaling portal allows everyone to send their information on the presence and abundance of the insect. These data refine the distribution maps. We can send a photo of the mosquito, more or less crushed. After a bite, no precautions need to be taken, unlike ticks. The chances of being infected with dengue fever are still close to zero in mainland France.

The tiger mosquito continues its meteoric rise in France

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