What specifically are we observing in this month of October?
Tiger mosquitoes are still around even though they shouldn’t be at this time of year. But the tiger mosquito is a “vector”: it carries 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. 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 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. Also in 2010 we had the first autochthonous case of chikungunya and in 2019 the first case of Zika.
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 locations further north, which will offer it a space where the temperatures will be more and more suitable.
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.