Surveillance for dengue, chikungunya, and Zika is based on mandatory reporting. From May 1 to November 30 of each year, during the active season of mosquito vectors, this surveillance is intensified through investigations of each case and the implementation of prevention measures in collaboration with the Regional Health Agencies (ARS) and mosquito control operators (see surveillance system and partners).

Enhanced surveillance for chikungunya, dengue, and Zika ended on November 30, 2024.

Episodes of local transmission of dengue, chikungunya, and Zika

The dengue, chikungunya, and Zika viruses, transmitted by mosquitoes of the genus Aedes, and the West Nile virus, transmitted by Culex mosquitoes, are subject to surveillance in mainland France, which aims primarily to prevent and/or limit the establishment of a transmission cycle for these arboviruses. Since its initial introduction in 2004, the Aedes albopictus mosquito (tiger mosquito), a vector for these viruses, has spread to the vast majority of mainland France. Culex mosquitoes are ubiquitous.

This surveillance relies on mandatory reporting (MR) of all biologically confirmed cases, both imported and indigenous. It is reinforced, in particular, by the automated transfer of results from the main laboratories performing these diagnoses and by raising awareness among healthcare professionals during the mosquito activity period from May 1 to November 30 to address the risk of local transmission.

The preliminary report for the 2024 season indicates 11 outbreaks of local dengue transmission totaling 83 cases (Table 1). This represents the highest number of outbreaks and indigenous cases identified since the implementation of enhanced surveillance in 2006. These outbreaks occurred primarily in Provence-Alpes-Côte d’Azur and Occitanie (Figure 1). An autochthonous case of chikungunya was reported for the first time in Île-de-France, one year after the identification of the first autochthonous dengue transmission outbreak (3 cases) in that region. For each outbreak, entomological and epidemiological investigations were immediately launched, accompanied by vector control measures. Measures to secure products derived from the human body were also implemented, in accordance with the recommendations of the High Council for Public Health.

Thanks to the epidemiological investigations conducted, the imported case at the origin of the transmission was identified in 3 of the 11 outbreaks investigated. The imported primary cases had returned from French Guiana, Réunion, and Indonesia.

For 8 of the 11 local outbreaks, the dengue virus serotype was identified. Serotype 1 (DENV-1) was identified in 4 outbreaks, serotype 2 (DENV-2) in 3 outbreaks, and serotype 3 (DENV-3) in one outbreak.

The transmission zone within a single transmission cluster did not exceed a radius of 400 meters.

These data confirm the increased risk of local transmission of arboviral diseases spread by Aedes albopictus observed in 2022, a year in which more locally acquired cases of dengue were reported (66 cases) than during the entire period since the first emergence of dengue (48 cases) in 2010. Similarly, the northward geographic expansion of the risk of local transmission of these arboviruses is confirmed.

Imported cases from May 1 to November 30, 2024

As part of enhanced surveillance, 2,120 imported dengue cases were identified, including 1,885 in departments where the presence of Aedes albopictus has been documented. In addition, 25 cases of chikungunya (n=24 in departments colonized by Aedes albopictus) and 6 cases of Zika (n=6 in colonized departments) were also reported. A dengue-chikungunya co-infection was also reported.

Record number of imported dengue cases since January 2024

As of December 17, 2024, 4,694 imported dengue cases had been reported since January 1, 2024, marking the highest annual number of reported cases since surveillance began in 2006 (Figure 2).

These figures come amid an exceptional year for dengue globally. In the Americas, with a total of more than 12 million estimated cases, 2024 set a record for the highest number of cases since dengue surveillance began in 1980. The previous record, set in 2023, stood at 4.5 million cases.

Major dengue outbreaks affected Guadeloupe, Martinique, and French Guiana from the summer of 2023 through the summer of 2024. These outbreaks, combined with significant travel between these territories and mainland France, resulted in a record number of dengue cases imported from these territories.

Since early November 2024, Guadeloupe has once again been affected by a dengue outbreak.

Imported cases of dengue, chikungunya, and Zika in mainland France

From January 1 to April 30, 2024, the following cases were reported through mandatory reporting (figures updated on September 3):

• 2,271 imported cases of dengue

• 6 imported cases of chikungunya

• 2 imported cases of Zika

From May 1, 2024, to November 26, 2024, the following were identified in mainland France:

• 2,028 imported cases of dengue, including 1,808 in departments where the presence of Aedes albopictus has been documented

• 21 imported cases of chikungunya (n=20 in departments colonized by Aedes albopictus)

• 5 imported cases of Zika (n=5 in departments colonized by Aedes albopictus)

West Nile Virus Surveillance Data for 2024

West Nile virus surveillance identified 39 locally acquired cases in the departments of Provence-Alpes-Côte d’Azur, Occitanie, and Nouvelle-Aquitaine, including, for the first time, in the Pyrénées-Atlantiques department (Figure 3). These data also confirm the increased risk of West Nile virus infection, with a significant number of cases and the spread of this risk to the southwest.

In Europe, more than 1,300 locally acquired cases of West Nile virus were reported in 2024. Italy (449 cases) and Greece (217 cases) are the most affected countries.

Map of human West Nile virus cases in mainland France, 2024 season

Situation in Europe

• Dengue: Outbreaks of local transmission in Europe (ECDC)

• Chikungunya: Outbreaks of local transmission in Europe (ECDC)