Heat in France: expect an increase in viruses "exotic" – Orange messages

published on Thursday, October 27, 2022 at 05:18

More high temperatures, mosquitoes and cases of “indigenous” dengue fever in France: Anna-Bella Failloux, a specialist in mosquito-related diseases at the Pasteur Institute, explains that we must expect an increase in viruses that were classically “exotic”.

What specifically are we observing in this month of October?

Tiger mosquitoes are still present, but they shouldn’t be there at this time of year. The tiger mosquito is a “vector”: in fact, it is “competent” to transmit viruses that will be pathogenic to humans, such as dengue fever.

We have identified more than 60 cases of “indigenous” dengue fever: such a number has never happened. A few years ago, it even seemed unimaginable. The virus enters France through people returning from abroad, to places where it circulates a lot, especially in the tropics.

By biting a person, the tiger mosquito absorbs the blood and allows the virus to pass inside its body to the salivary glands. When he bites again, he injects this virus again: this is how transmission works and how autochthonous cases arise in people who have not left the territory.

What can we expect in the future?

Mosquito-related diseases, classically “exotic”, are now able to be transmitted by temperate mosquitoes in France.

The first case of autochthonous dengue fever in France dates from 2010. We also had the first autochthonous case of chikungunya in 2010 and the first case of Zika in 2019.

With climate change, more mosquitoes and therefore more viruses are to be expected. Instead of having mosquitoes from the beginning of May, we will see them from April. And they will stay even later after the summer is over.

The warmer it is outside, the shorter the mosquito’s development cycle. It takes ten days between egg and adult. But if the temperature rises by, for example, 5 degrees, the cycle is shortened to eight days. Therefore, in the future we will have mosquito densities that will increase because they will take 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 have to stay alert, try to anticipate. Virus numbers are expected to rise as people continue to travel and the severely disrupted ecosystems around us become ready for mosquitoes. There is no widely used vaccine for dengue, and tiger mosquitoes are resistant to the insecticides we use. Dengue fever kills between 30,000 and 50,000 people worldwide each year.

Various methods are being tested to eradicate it. One of them is the introduction into nature of mosquitoes infected with bacteria blocking the circulation of the virus. Today it is done in New Caledonia and Polynesia.

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