The tiger biting the mosquito is getting farther and farther north

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

Native to the forests of Southeast Asia, this mosquito has resided in temperate regions for 40 years. In Europe, it bites in more than 20 countries. Reported in France in 2004 in Menton (Alpes-Maritimes), it now has 67 departments. Mathematical models predicted its expansion, but we were surprised at the speed.” On the website of the Ministry of Health, a map of the presence of tiger mosquitoes in France shows a rapid increase. From La Rochelle to Strasbourg, the Regional Health Service is carrying out insect control operations. In the West, present from Vendée to Mayenne, it progressing in the Loire-Atlantique “where it will become abundant” note medical entomologists. Mosquito also discovered in Brittany where the Regional Health Authority is currently increasing surveillance.

Colonization by road

Easily identifiable by its color, black and white stripes, Aedes albopictusare original, compared with 65 other species of mosquitoes in France, 15 of which bite people. Not just because it burns during the day, instead of waiting at night. Its huge genetic variability is quite astonishing. This is one of the reasons why it adapts to very different environments.”

Climate change is not the main driver of its spread: its colonization follows highways and major roads. One female enters the car, the female goes further and her eggs reside in another area”. The recent heatwave has not necessarily been beneficial to the insect: a study at a mosquito farm found mortality rates as high as 31 degrees Celsius.

Mosquito bites can cause allergic reactions. Didier Fontenille believed it was a nuisance, who quoted people’s testimony “Bite ten times a day near Montpellier, in Nice, Marseille and Toulon. It is the main species of mosquito in the town, in the south of France.”

It is the possibility of virus transmission that worries specialists. The rate is very low today: only 82 people were bitten by mosquitoes in France, within 10 years, due to the mosquito that carries dengue fever, in addition to Zika and chikungunya. These “indigenous cases” were infected by a mosquito that had bitten an infected person a few days earlier, returning from a tropical region where dengue fever was endemic. Dengue fever cases will increase in France, it is inevitable, The entomologist’s estimate, especially since tourism has returned. We expect 10 or 20 self-medicating cases this year.”

Hundreds of “imported” dengue cases are also reported each year in France. They are tourists from abroad, from Reunion where dengue fever is endemic since 2018 to Polynesia.

Release sterile mosquitoes

How can this annoyance be reduced? Tiger mosquitoes thrive in small water reserves: a dish under flowers, children’s toys left in the garden, a gutter that hasn’t been cleaned. The first solution, which has been promoted in communities in Occitania, involves emptying these containers where the water is stagnant.

Several types of traps exist, which are not always effective, as an ANSES study has shown. Researchers are improving them by 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, which are dropped in reasonable places. They will mate with wild females whose eggs will not hatch.”

This method has been used in Reunion, as part of a project involving IRD and ARS: 300,000 infertile males released per week halved the mosquito population in the control area. Other scientists are looking for biological insecticides: viruses that kill only these mosquitoes.

Everyone can join the fight against this mosquito. ANSES . reporting portal allows people to submit their information about insect presence and abundance. These data refine the distribution maps. We can send a photo of the mosquito, more or less crushed. After being bitten, there is no need to take precautions, unlike ticks. The likelihood of being infected with dengue remains close to zero in mainland France.

Nicolas GUILLAS.

The tiger biting the mosquito is getting farther and farther north

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