Crimean-Congo hemorrhagic fever (CCHF) is a tickborne disease caused by CCHF virus (CCHFV) (species Orthonairovirus haemorrhagiae, genus Orthonairovirus, family Nairoviridae, order Bunyavirales). Endemic in Africa, the Middle East, Asia, and Eastern Europe, CCHF has expanded to Western Europe (1). Repeated detection of CCHFV in Spain (2) raises questions about its circulation in neighboring countries, such as Portugal, Italy, and France.

In Corsica, a French Mediterranean island, a seroprevalence study of CCHFV conducted in livestock (cattle, goats, and sheep) during 2014–2016 showed an overall seroprevalence of 9.1%, and cattle harbored the highest rates (3). A subsequent surveillance study of 8,051 ticks collected from wild (wild boar, deer, and mouflon sheep) and domestic (cattle, horses, sheep) animals during 2016–2020 failed to detect CCHFV or nairovirus RNA (4).

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Figure. Phylogenetic analysis of Crimean-Congo hemorrhagic fever virus in ticks collected from cattle, Corsica, France, 2023. Map at left shows locations of cattle from which ticks were collected at the slaughterhouses...

Since 2022, we have continued CCHFV surveillance by collecting ticks from cattle at 2 slaughterhouses >2 times/month. Cattle originate from a broad geographic area, and the national ear-tag identification system enables tracing of each animal’s origin and farm owner (Figure). We identified ticks by using taxonomic keys, then pooled ticks by species, sex, development stage, study site, and animal host, as previously reported (4). We spiked each pool, consisting of 1–6 ticks, with a predefined amount of MS2 bacteriophage for monitoring nucleic acid extraction, reverse transcription PCR (RT-PCR), and nucleic acid amplification (5). We used MagMAX Viral/Pathogen Ultra Nucleic Acid Isolation Kit (Thermo Fisher Scientific, https://www.thermofisher.com) to purify nucleic acids. We tested each sample by using 2 real-time RT-PCRs, 1 targeting the large (L) RNA segment (2) and 1 targeting the small (S) RNA segment (6). We used the SuperScript IV One-Step RT-PCR System Kit (ThermoFisher) to design 28 CCHFV-specific pairs of primers to amplify the S, medium (M), and L segments (Appendix). We sequenced PCR products by using S5 Ion Torrent technology (ThermoFisher). We determined the best model by using the maximum-likelihood method and performed phylogenetic analyses by using MEGA6 software (7) (Figure).

During June 2022–July 2023, we collected 5,165 ticks from 465 cattle and grouped ticks into 1,491 pools. Tick species consisted of 2,390 (46.27%) Rhipicephalus bursa, 1,103 (21.35%) Hyalomma marginatum, 750 (14.52%) Boophilus annulatus, 507 (9.81%) Hyalomma scupense, 238 (4.60%) Haemaphysalis punctata, 127 (2.45%) Ixodes ricinus, 48 (0.92%) Rhipicephalus sanguineus, and 2 (0.03%) Dermacentor marginatus. A total of 24 (1.70%) pools collected from 5 cattle from southern Corsica tested positive by the L-RNA assay (Table). Nineteen of the 24 tick pools were collected from 1 animal (no. 4039) (Table). Partial sequences for S (1,340 bp), M (4,894 bp), and L (11,275 bp) segments were obtained from animal nos. 2478 (pool 417) and 4039 (pool 1207) (Table). The effective detection of CCHFV genome is strongly supported by the formal exclusion of contamination because no CCHFV strain or genome had been previously processed in the laboratory, the PCR systems used can distinguish genomic RNA from the positive control (6), and the CCHFV sequences obtained were original and unambiguous.

The obtained S and M segment sequences constituted a monophyletic group belonging to genotype I (Africa 1), whereas the L segment sequence grouped with genotype III strains (Africa 3) (Figure). The sequences of all 3 segments of the CCHFV from Corsica are closely related to 2 sequences from Senegal corresponding to strains identified in the 1970s and likely represent strains reassorted in Senegal. Whether those strains are typical of strains from Senegal or have been circulating in other parts of Africa requires additional investigations.

Our results suggest that CCHFV strains circulating in Corsica and Spain have distinct origins. In Spain, genotype III is the most widespread and is most often detected in H. lusitanicum ticks (2), a species not yet identified in Corsica. Trans-Saharan migratory birds carrying H. marginatum ticks are the most likely source of CCHFV strains entering Corsica (6). Examination of the main bird migration routes suggests that 2 different migratory corridors link Spain and Corsica to Africa; mainly, but not exclusively, West Africa for Spain and Central Africa for Corsica (6). Those migration routes also could explain the different origin of CCHFV strains circulating in Corsica and in Spain.

Our results provide evidence for established CCHFV circulation in Corsica because detection occurred at 2 distinct sites in the southeastern and central western parts of the island. In addition, our results provide evidence for infection in cattle because multiple CCHFV-positive ticks were found on the same animal. CCHFV detection in feeding ticks is indicative of virus circulation within the cattle population but does not elucidate the role of ticks in virus transmission. Our results must be interpreted by considering previous serologic evidence of CCHFV circulation in cattle in Corsica (3), the presence of competent vectors locally (4), and recent reports of CCHFV detection in southern mainland France (10). The threat of possible continuous expansion and circulation of the virus over Western Europe should not be disregarded. Healthcare professionals and other groups at risk for infection, including hunters and farmers, should be informed about CCHFV circulation in Corsica.

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