Surveillance and control efficacy of the Bergerac, France, 2025 chikungunya outbreak

Abstract The spread of the highly invasive mosquito, Aedes albopictus, across Europe, combined with climate change and human travel and trade, has led to new epidemic threats from mosquito-borne viruses, most significantly dengue and chikungunya, which are increasing in frequency and magnitude. In 2025, mainland France has seen a record number of autochthonous cases and outbreaks of chikungunya, spread across multiple locations, primarily introduced by travellers from the French Overseas Territory of La Réunion which is experiencing severe chikungunya outbreaks. Here, we describe one of the largest French outbreaks and subsequent control measures in the city of Bergerac, Dordogne, which resulted in 102 cases as of 5th November 2025. Using a state-of-the-art mathematical model, we accurately predict the course of the outbreak, suggesting that the initial control measures in the first four weeks after the discovery of the outbreak, limited in their intervention radius, had little effect on reducing the number of cases, given the high incidence and the wide geographic extent of viral circulation. However, subsequent more widespread and intense control efforts, combined with likely increased public awareness, substantially reduced case numbers. These findings underscore the need to tailor control measures to intensity and scale of viral circulation combined with effective preventive and proactive arbovirus surveillance. We conclude that adulticides combined with public awareness campaigns can be effective for public health protection and are an important part of mitigating against the risk of Aedes-borne arboviruses and the ongoing outbreaks in mainland France. Competing Interest Statement GL and AM are employed by Altopictus. The authors declare no potential conflict of interest. Funding Statement This study was funded by the NERC IAPETUS DTP (Grant NE/S007431/1), the EPSRC (Grant EP/Y017838/1 and EP/Y017919/1) and the BBSRC-Defra (Grant BB/X018113/1). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All case data is publicly available via Santé Publique France https://www.santepubliquefrance.fr/regions/nouvelle-aquitaine/documents/bulletin-regional/2025/chikungunya-dengue-et-zika-en-nouvelle-aquitaine.-bulletin-du-9-octobre-2025 and https://www.santepubliquefrance.fr/maladies-et-traumatismes/maladies-a-transmission-vectorielle/chikungunya/documents/bulletin-national/chikungunya-dengue-zika-et-west-nile-en-france-hexagonale.-bulletin-de-la-surveillance-renforcee-du-5-novembre-2025. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability All model code is available on GitHub https://doi.org/10.5281/zenodo.17534800. All case data is publicly available via Santé Publique France https://www.santepubliquefrance.fr/regions/nouvelle-aquitaine/documents/bulletin-regional/2025/chikungunya-dengue-et-zika-en-nouvelle-aquitaine.-bulletin-du-9-octobre-2025 and https://www.santepubliquefrance.fr/maladies-et-traumatismes/maladies-a-transmission-vectorielle/chikungunya/documents/bulletin-national/chikungunya-dengue-zika-et-west-nile-en-france-hexagonale.-bulletin-de-la-surveillance-renforcee-du-5-novembre-2025.