Dengue, Zika, Chikungunya... All the questions raised by these diseases carried by the tiger mosquito

Chigungunya, Dengue, Zika... Behind these disease names lies a single culprit: the mosquito. The same mosquito that flies close to our ears in the middle of the night or sneaks in through the smallest open window at the end of the day to be served as its nocturnal snack.

While the situation may seem humorous in its description, the reality is quite different. In a context of intense heat, these diseases, once exclusively tropical, are taking hold in metropolitan France, and this is a cause for concern for health authorities.

Indeed, as of July 1, 2025, Public Health France has already recorded seven episodes of indigenous chikungunya transmission in France, in five regions including Provence-Alpes-Côte d'Azur. And what concerns the authorities is the early onset of symptoms over the year. This year, the first symptoms appeared between May 27 and June 27, while in previous years, symptoms were observed later in the year. In this case, in 2024, a year when the dengue epidemic was particularly severe, the first case was identified in June.

In view of this, here are the questions that arise regarding the development of these diseases.

How many imported cases have been recorded in France and PACA?

According to Public Health France, which issues a surveillance bulletin every week, between May 1 and July 1, 2025, there were 496 imported cases of dengue fever, 712 of chikungunya and 1 case of Zika.

In Paca, between May 1 and July 1, 64 imported cases of chikungunya were recorded in the region, 59 cases of dengue fever and 1 case of Zika.

Where do imported cases come from?

For dengue, imported cases come mainly from three destinations: Guadeloupe, Martinique and French Polynesia .

Imported cases of Chikungunya come almost exclusively from territories in the Indian Ocean.

In particular, there have been 55 imported cases of Chikungunya from Réunion . This situation is partly linked to the epidemic in this territory, which has been on a scale unprecedented for twenty years. While the epidemic is coming to an end in the overseas department, the "threat" has spread to mainland France.

To a lesser extent, one case of Zika has been reported, a traveler returning from Thailand.

How are these diseases transmitted?

They are transmitted to humans through a bite by female mosquitoes of the genus Aedes, but also sometimes the tiger mosquito (Aedes albopictus). "When a mosquito feeds on the blood of an infected person, the virus replicates in its intestine and then reaches the salivary glands," explains the Pasteur Institute. Under certain conditions, the mosquito becomes infectious within a few days and can then contaminate other people. The virus can also be transmitted, more rarely, from a pregnant woman to her baby, through transfusion or transplant.

What is an indigenous case?

An indigenous case corresponds to the situation where a person contracted the disease on national territory and did not travel to an area where the virus is circulating in the 15 days preceding the onset of symptoms.