[Molecular epidemiological investigation and genetic characteristics of the early stage of Chikungunya fever outbreak in Guangzhou City, 2025].

Abstract

Objective: To conduct a molecular epidemiological investigation and genetic characteristics of the local outbreak of Chikungunya fever in Guangzhou City in July 2025, clarify the source, genotype, and variation characteristics of the virus, and provide a scientific basis for traceability and prevention and control of the outbreak. Method: Epidemiological data and serum samples of confirmed cases were collected. The virus nucleic acid testing, whole genome sequencing, phylogenetic tree reconstruction, and E1/E2 protein amino acid site analysis were performed. Results: By August 6, 2025, 104 autochthonous Chikungunya cases had been confirmed in Guangzhou City, showing a spatially scattered transmission pattern with limited cluster potential in areas such as Xintang Town. Fifty-one full-genome sequences were obtained, all belonging to the East/Central/South African (ECSA) genotype, Central African subclade, with a similarity of 99.96% to the Réunion Island strains (2024-2025). Fifteen amino acid mutations were identified in E1/E2 proteins, of which 13 were unique, including adaptive mutations such as E1-A226V and E2-I211T. Conclusion: The outbreak is caused by a single imported ECSA-genotype strain, potentially from the Indian Ocean region. There may be a risk of small-scale outbreaks in Guangzhou City. Continuously strengthening mosquito-borne disease surveillance, early warning systems, and etiological monitoring is significant for disease prevention and control.