Summary

Since 2004, when it was first identified in the Alpes-Maritimes department, the “tiger” mosquito Aedes albopictus—a vector capable of transmitting the dengue, chikungunya, and Zika viruses—has gradually expanded its geographic range in mainland France.

Present in Île-de-France since 2015, when its presence was confirmed in the Val-de-Marne department, Aedes albopictus is considered to be established and active in municipalities across all departments in the region except Val-d’Oise.

To combat the risk of arboviral diseases in metropolitan France, an integrated surveillance system was established in 2006. It relies on epidemiological surveillance based primarily on the mandatory reporting (DO) system for biologically confirmed cases. Surveillance is intensified during the mosquito’s active period (May 1 to November 30) by tracking down cases not reported through the mandatory reporting system, identified using data from medical testing laboratories. The identification and investigation of all these cases help guide vector control (LAV) efforts, implemented by mosquito control operators, whose objective is to combat the risk of an autochthonous transmission cycle establishing itself in mainland France during the mosquito activity period.
This bulletin presents the arbovirus surveillance system in mainland France and provides epidemiological and entomological summaries of the enhanced surveillance seasons for 2019 and 2020 in Île-de-France.

Key Points

• Initially limited to departments where the presence of Aedes albopictus has been confirmed, the enhanced surveillance system was expanded in 2020 to all metropolitan departments.

• In 2019, the departments in Île-de-France covered were Paris (75), Seine-et-Marne (77), Essonne (91), Hauts-de-Seine (92), Seine-Saint-Denis (93), and Val-de-Marne (94).

• 252 cases were reported during the 2019 season, primarily imported dengue cases, mostly from Southeast Asia.

• 419 cases were reported during the 2020 season, mainly imported dengue cases originating primarily from the Caribbean.

• No secondary local transmission was identified in the region during these two seasons.

• The estimated number of viremic cases present for at least one day in the Île-de-France region was 191 in 2019 (75.8% of cases) and 344 in 2020 (82.1% of cases).

• Despite the impact of the COVID-19 pandemic on travel in 2020, 609 entomological surveys were conducted compared to 259 in 2019, and 8 adulticide treatments were carried out compared to 3 in 2019.

• Two new diseases have been notifiable since May 12, 2021: West Nile Virus (WNV) and tick-borne encephalitis (TBE).