Widespread circulation of Crimean-Congo haemorrhagic fever virus in ticks, Corsica (France), 2024

Crimean-Congo Haemorrhagic Fever is a severe tick-borne viral disease with a high fatality rate. This study aimed to advance the understanding of CCHF virus (CCHFV) in terms of geographical spread and genotypic characterization by investigating its detection in ticks collected from cattle, one year after the first detection of CCHFV in Corsica. From 2024 to 2025, we collected ticks from cattle, with standardised sampling occurring twice per month. Ticks were screened for CCHFV RNA by RTq-PCR. Genome sequencing and phylogenetic analyses were performed. Blood samples from a subset of these cattle were tested for CCHFV antibodies using a commercial enzyme-linked immunosorbent (ELISA) test. Among the 13,577 ticks collected, CCHFV RNA was detected in 61 pools (1.6%) out of the 3803 tested. We identified CCHFV African genotype III in ticks collected from cattle at different sites in northern and southern Corsica. However, two tick strains showed a reassortant profile, with the S and L segments belonging to genotype III and the M segment belonging to genotype I. Data also showed that our strains clustered with strains isolated in African and Western European countries. The overall IgG anti-CCHFV seroprevalence in cattle was 8.44% [95% CI: 6.27% - 11.06%]. This study provides new insights into the spatial and temporal distribution of CCHFV in Corsica and confirms the wider-than-expected distribution and variability of CCHFV in Corsica. Therefore, our findings confirm the genetic variability inside the CCHFV genotypes and their introduction to Corsica from other countries.