Santé publique France has identified 25 locally transmitted cases of chikungunya in mainland France as of August 17, the national public health agency announced on Wednesday, August 19. The cases occurred across three separate outbreaks, with the majority reported in the Gironde department and additional infections found in Tarn.
The public health agency also confirmed four locally transmitted cases of dengue fever across three distinct episodes in Tarn, Hérault, and Dordogne. Both viral illnesses are spread by the invasive tiger mosquito, which carries the infection from person to person.
Santé publique France is the government organisation responsible for tracking infectious diseases and protecting public health across the nation. In its weekly report, the agency noted that the tiger mosquito has expanded far beyond its traditional habitats. Formerly restricted to tropical and subtropical regions, the insect is now established in 83 of metropolitan France's departments.
Mosquito spread and climate factors
The active period for tiger mosquitoes in mainland France now spans from May to November each year. Public health officials warned that the steady presence of local chikungunya infections demonstrates that the virus has become firmly established in the country over recent years.
A combination of climate change, global trade, and rapid urbanisation has enabled tiger mosquitoes to colonise northern and temperate areas where they were entirely absent a few decades ago. As mosquito populations thrive in warmer temperatures, local transmission of tropical diseases has become a recurring health concern in Europe.
Chikungunya and dengue are mosquito-borne viral infections that typically cause high fever, severe joint pain, headaches, and physical exhaustion. While native to warmer climates, these viruses spread locally when a tiger mosquito bites an infected traveler and then bites another person in the local community.
Regional comparison and West Nile virus
The 25 chikungunya cases recorded this year mark a substantial decline from the previous year, when health authorities logged more than 800 autochthonous cases across mainland France. However, officials stated that last year's exceptional total was driven in part by cases imported from Réunion, a French overseas island in the Indian Ocean that was hit by an epidemic unprecedented in about 20 years.
In addition to chikungunya and dengue, Santé publique France reported that 18 cases of West Nile virus have been registered since the start of summer. Unlike chikungunya and dengue, West Nile virus is transmitted by a common mosquito species traditionally native to mainland France.
The public health agency confirmed that West Nile cases were identified not only in the southern regions of France but also in the Paris area. West Nile fever, which can cause neurological complications in rare instances, is routinely monitored by European health authorities during the summer and autumn months.
