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. 2025 Jun;30(22):2500344.
doi: 10.2807/1560-7917.ES.2025.30.22.2500344.

Genomic insights into the re-emergence of chikungunya virus on Réunion Island, France, 2024 to 2025

Etienne Frumence  1   2 , Géraldine Piorkowski  3 , Nicolas Traversier  1   2 , Rayane Amaral  3 , Muriel Vincent  4 , Ambroise Mercier  2 , Nazli Ayhan  3   5 , Laurent Souply  2 , Laura Pezzi  3   5 , Clément Lier  2 , Gilda Grard  3   5 , Guillaume André Durand  3   5 ; Chikungunya genomics diagnostic laboratory network  6 ; Xavier Deparis  7 , Fabian Thouillot  4 , Xavier de Lamballerie  3   5 , Raphaelle Klitting  3   5 , Marie-Christine Jaffar-Bandjee  1   2 ; Chikungunya genomics diagnostic laboratory network
Collaborators, Affiliations

Genomic insights into the re-emergence of chikungunya virus on Réunion Island, France, 2024 to 2025

Etienne Frumence et al. Euro Surveill. 2025 Jun.

Abstract

Chikungunya virus re-emerged on Réunion Island in August 2024, 18 years after a first major outbreak. Analysis of 173 genomes from the current epidemic reveals a monophyletic clade with mutations linked to adaptation to Aedes albopictus mosquitoes, including E1-A226V. Bayesian inference suggests only brief cryptic circulation before detection. The same lineage was also detected on Mayotte Island in March 2025. Continued spread and confirmed travel-related cases in mainland France and globally highlight the risk of wider regional and international dissemination.

Keywords: Chikungunya; Genomic analysis; arbovirus; emergence; molecular epidemiology; surveillance.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Weekly chikungunya cases and CHIKV genome sequencing data from Réunion Island, showing low-level circulation until late 2024 and a sharp increase with a peak between weeks 13 and 17 of 2025.
Figure 1
Temporal distribution of confirmed chikungunya cases (n = 51,558) and sequenced CHIKV genomes (n = 1,564), Réunion Island, France, August 2024–May 2025
Phylogenetic tree showing chikungunya virus genomes from Réunion Island (2024–25) grouped within the East-Central-South African genotype. The tree highlights the virus lineages causing the current outbreak and related sequences from Central Africa and mainland France. Key mutations are indicated.
Figure 2
Phylogenetic tree of CHIKV genomes from 1952–2025 (n = 2,729) and the Réunion Island clade, France, 2024–2025 (n = 201)
See this image and copyright information in PMC

References

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