How A Réunion Island Outbreak Sparked France’s Record Chikungunya Season

A surge of imported cases from Réunion Island triggered France’s earliest chikungunya play ever, testing nan limits of its surveillance strategy and exposing Europe’s increasing vulnerability to mosquito-borne diseases.

Rapid communication: Multiple early section transmissions of chikungunya virus, Mainland France, from May 2025. Image Credit: khlungcenter / Shutterstock

In a caller accelerated connection successful nan diary Eurosurveillance, researchers from France's nationalist wellness agency item nan existent script of nan chikungunya illness wrong nan country. Specifically, nan aftermath of a ample 2025 chikungunya outbreak connected Réunion Island led to a surge of imported cases successful mainland France, triggering an unusually early and wide play of section transmission.

The study highlights how, by July 10, 2025, 10 section outbreaks involving 27 group had been identified crossed 5 French regions. The first section transmission occurring successful May (with denotation onset May 27) is nan earliest recorded for immoderate arbovirus (chikungunya, dengue, aliases Zika). These events, driven by nan Aedes albopictus (tiger) mosquito, awesome an escalating threat from arboviral diseases successful Europe and importantly strain surveillance and consequence systems.

Map of nan autochthonous transmission events of chikungunya virus, Mainland France, May–10 July 2025 (n = 27)

Background

Chikungunya is simply a mosquito-transmitted viral illness caused by nan chikungunya virus (CHIKV), an RNA microorganism successful nan alphavirus genus of nan family Togaviridae. Formally a tropical illness localized successful Africa and Southeast Asia, nan scope description of its vector (the Aedes albopictus mosquito) has allowed chikungunya to found itself globally, peculiarly successful ample parts of Europe, including France.

The illness is characterized by precocious fever and mean to terrible associated symptom that manifests abruptly wrong a week of infection. These symptoms whitethorn besides beryllium accompanied by musculus pain, headache, fatigue, and rashes.

Viral transmission follows a straightforward and well-documented shape – an infected individual (termed an "imported case") travels from an outbreak area to a region wherever tiger mosquitoes are present. If a section mosquito bites that personification during their viraemic shape (when nan microorganism is successful their blood), it tin transmit nan microorganism to different section people, creating an "autochthonous" aliases section transmission chain.

To combat this, France operates an enhanced surveillance strategy from May to November, aiming to quickly observe imported cases and instrumentality vector power to forestall section spread. However, successful early 2025, this strategy faced important challenges owed to a monolithic chikungunya outbreak connected Réunion Island, a French overseas territory (Indian Ocean).

About nan Report

The coming study represents a accelerated connection detailing nan real-time findings from France's mandatory surveillance strategy for Aedes-borne viruses. Conducted by researchers from Santé publique France (the French National Public Health Agency), nan study intends to forestall aliases limit section chikungunya transmission by quickly identifying and responding to some imported and autochthonous cases.

Surveillance information is collated and synthesized via regular monitoring of laboratory results and epidemiological investigations of confirmed cases. When a lawsuit is confirmed, nationalist wellness authorities question and reply nan diligent to find their recreation history and found nan apt spot of infection. If a lawsuit has nary recreation history, it is classified arsenic autochthonous, initiating intensive section response.

Chikungunya mitigation measures and intensive section consequence include: 1. Door-to-door lawsuit uncovering to place different imaginable infections, including tracing superior imported cases (successful successful 4/10 outbreaks), and 2. Vector power measures, specified arsenic eliminating mosquito breeding sites and spraying insecticides and larvicides successful nan affected area.

Report Findings

The study credited nan Réunion Island outbreak betwixt January and April 2025 pinch a mostly (n = 484; 78%) of nan 620 imported chikungunya cases pinch denotation onset documented successful mainland France betwixt May and June 2025. By July 10, 2025, 1,911 imported cases had been notified, 89% linked to Réunion Island – nan highest connected grounds since French surveillance began successful 2006. Notably, much than 86% of imported cases were viraemic during their enactment successful mainland France.

This monolithic influx triggered 10 autochthonous outbreaks comprising 27 cases identified by July 10. The largest cluster (unusually ample compared to others) was successful Salon-de-Provence pinch 13 people.

Critically, this marks nan earliest arbovirus transmission play successful France's history. Prior to 2025, nan earliest first lawsuit occurred connected June 12, pinch only 3 of 53 antecedently documented outbreaks starting successful June. The median 9-day reporting hold for imported cases facilitated accelerated response.

The outbreak successful Lipsheim (Grand Est) is peculiarly important arsenic nan first section transmission successful this precocious colonized region, wherever Aedes albopictus was only detected successful 2015.

Conclusions

The coming study highlights France's escalating arbovirus situation and suggests that this is only nan commencement of nan expanding threat of mosquito-borne diseases successful Europe. The operation of a ample overseas outbreak (and its associated influx of cases), a Réunion strain well-adapted to Aedes albopictus, and nan mosquito's northward description has demonstrated that section transmission tin hap overmuch earlier successful nan play than antecedently thought, moreover erstwhile vector densities are presumed to beryllium low.

While nan accelerated discovery and containment of these first outbreaks item nan effectiveness of France's surveillance system, nan resource-intensive quality of door-to-door investigations and vector power measures raises concerns astir nan system's capacity if transmission trends proceed to increase. This study underscores nan urgent request for European policymakers to expect this increasing consequence done dedicated funding, contingency planning, and research.