French regions are waging war against tiger mosquitoes as the country records rising cases of tropical diseases such as dengue, zika and chikungunya.

Since Jan. 1, France has already seen 1,123 imported cases of dengue, 728 imported cases of chikungunya and four imported cases of zika. In May alone, French health authorities said they recorded 225 cases of chikungunya, 152 cases of dengue and one case of zika — also all imported.

The numbers raise alarm for health authorities, who are warning people to watch out for tiger mosquitoes, the insects most responsible for carrying and spreading the diseases.

While a person infected with dengue or chikungunya cannot pass the virus to another person, they can infect other mosquitoes which can further spread the disease. Zika can be transmitted from an infected person through sexual intercourse.

The southeastern region of Auvergne-Rhône-Alpes — which was the second most affected French region in 2024 and already recorded 68 cases of chikungunya and dengue in May — has issued recommendations to help eradicate the mosquitoes, which have spread to over one quarter of the municipalities in the region.

They urge people to store, empty or cover containers that could accumulate water, which can serve as breeding sites for mosquitoes, and take precautions against mosquito bites, especially when traveling. They’re also sending a plea to mayors and other local officials to take action to control the spread of mosquitoes.

It’s not just France: Belgium’s public health institute warned that tiger mosquitoes had been found in twice as many locations in 2023 compared with the previous year. The Flemish Department of Public Health also launched a new campaign to minimize the spread of the tiger mosquitoes earlier this month, urging people to play their part to stop the invasive insect from breeding.

Tiger mosquitoes are increasingly spreading across Europe as climate change makes environmental conditions more habitable, raising the risk that vector-borne diseases once limited to the tropics become endemic across the continent.