After a summer marked by high temperatures and gigantic fires, autumn is turning out to be much milder than normal, aggravating the drought according to Météo France in the south of the country. With these high temperatures, more and more mosquitoes and cases of “indigenous” dengue are detected in France. Anna-Bella Failloux, specialist in mosquito-related diseases at the Institut Pasteur, explains that we must expect an increase in viruses which were classically “exotic”.
What do we observe in particular in this month of October?
The tiger mosquitoes are still present, but they should no longer be there at this time of year. The tiger mosquito is a “vector”: it is in fact “competent” to transmit viruses which will be pathogenic for humans, such as dengue fever. We have identified more than 60 cases of “indigenous” dengue fever: such a number, it had never happened. It even seemed unimaginable a few years ago. The virus arrives in France via people returning from abroad, in places where it circulates a lot, especially in the Tropics.
By biting a human, the tiger mosquito absorbs blood, lets the virus pass inside its body into its salivary glands. When it bites again, it reinjects this virus: this is how transmission works and how autochthonous cases are generated in people who have not left the territory.
What can we expect in the future?
Mosquito-related diseases, classically “exotic”, are now capable of being transmitted by a temperate mosquito in France. The first case of autochthonous dengue fever in France dates from 2010. We had a first autochthonous case of chikungunya in 2010 as well, and a first case of zika in 2019. With climate change, we can expect more mosquitoes and therefore of viruses. Instead of having mosquitoes from the beginning of May, we will see them from April. And they will stay later after the summer is over.
The hotter it is outside, the shorter the mosquito’s development cycle. Between the egg and the adult, it takes ten days. But if the temperature increases for example by 5 degrees, the cycle is shortened to eight days. In the future, we will therefore have mosquito densities that will increase since it will take them less time to become adults.
Climate change will also offer them more space to colonize. Today, the tiger mosquito is installed in the south of France. It will settle there permanently and try to colonize other sites further north which will offer it a space where the temperatures will be more and more adapted to its development and survival.
Should we be worried?
We must remain vigilant, try to anticipate. Viruses are expected to rise as people continue to travel and heavily disrupted ecosystems around us will be primed for mosquitoes. In the case of dengue, there is no widely used vaccine and tiger mosquitoes are resistant to the insecticides we use. Dengue fever kills between 30,000 and 50,000 people a year worldwide.
Different methods are being tested to eradicate it. One of them consists in introducing into nature mosquitoes infected with a bacterium blocking the circulation of the virus. It is done today in New Caledonia and Polynesia.
Source: Europe1
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