Paris: “Mosquitoes are increasingly adapting to life with humans”

Zika, dengue fever, malaria, yellow fever, chikungunya: favored by global warming, deforestation and unbridled urbanization, the transmission of these infectious diseases by mosquitoes is increasingly scrutinized by researchers at the Pasteur Institute.

“Temperatures are increasing, living conditions are deteriorating: we are creating development conditions where mosquitoes adapt to life with humans,” underlines entomologist (insect specialist) Anna-Bella Failloux .

His team works on “the species of mosquitoes that live in the city with us: initially, they grew in tropical forests, took blood from animals; today, they lay eggs in the city in a plastic bucket of water, next to people they sting,” she summarizes.

Today, 80% of the world’s population runs the risk of being exposed to one or more infectious diseases long considered tropical, which kill more than a million people per year, mostly children, according to the World Health Organization. Health.

To study them, the Pasteur Institute announced on Tuesday that it would invest 90 million euros to build a “research center on infections linked to climate and the environment”, which will be built in 2028. “This will allow us to have all species of mosquitoes at the same time, in the same place,” explains Anna-Bella Failloux.

Out of 3,500 species of mosquitoes, only 15% bite humans. “Those that interest us are the Aedes aegypti and the Aedes albopictus (the tiger mosquito), which live where there is a significant human concentration and water which stagnates around houses due to lack of evacuation, as in the favelas of Rio,” describes the entomologist. If these two species are responsible for the transmission of several diseases to humans, many questions remain unanswered.

“Today, the malaria mosquito, Anopheles gambiae, cannot transmit the viruses of yellow fever, dengue, chikungunya, zika… even though it coexists with Aedes aegypti which, for its part, transmits,” continues Anna-Bella Failloux. “They live in the same place, bite humans in the same way, so how come only one of them transmits malaria?

To study the transmission of these viruses, researchers infect female mosquitoes – the only ones to bite. They are first “starved for 24 hours”, then “we fill a capsule covered with skin – generally pig intestine – with a mixture of blood and virus, which the female mosquito will come and bite “.

“The difficulty,” explains the researcher, “is to force them to eat, because it is not very appetizing. So we have lots of tips to attract them: we wear smelly socks, CO₂or a smell of apples. And “some only bite at night: we have to infect them in the dark, so it’s complicated.”

Within three years, this research should make it possible to draw up “risk maps” for the tiger mosquito, present on 80% of French territory, by testing “different populations of mosquitoes against 12 distinct viruses” . While mosquitoes have developed resistance to insecticides, “we need to make the fight as targeted as possible,” she concludes.