Zika virus infection in a traveller returning to France from Seychelles, 2024

Abstract

In August 2024, a case of Zika virus infection was identified in metropolitan France in a traveller returning from Seychelles. Genomic analysis confirmed that the strain belongs to the Asian lineage. Recent epidemiological findings provide the first evidence of ZIKV circulation in the western Indian Ocean region.

Zika virus (ZIKV) is an arthropod-borne flavivirus primarily transmitted in tropical regions by Aedes spp. mosquitoes. While large-scale outbreaks have occurred in Central and South America, in the Pacific and in South-East Asia,¹ there had been no prior evidence of ZIKV circulation in the Indian Ocean region until April 2024, when a case was imported into Italy by a traveller returning from Seychelles.²

In August 2024, a woman in her fifties was diagnosed with a ZIKV infection after returning to metropolitan France from a 3-week stay in Seychelles. Six days following her return, she developed a fever and rash, prompting her to seek medical advice. Although hospitalization was not required, she underwent a blood test due to suspicion of arboviral infection.

A serum sample obtained on the day of symptom onset was tested at INOVIE Labosud Garosud laboratory (Montpellier, France) and yielded a positive result by RT-qPCR for ZIKV using the ZIKV/Dengue Virus/Chikungunya Virus Real-Time PCR Kit (BioPerfectus) on the BeGenius® system (ELITech). After transfer of the serum to the French National Reference Center (NRC) for Arboviruses (Marseille), positive RT-qPCR result was confirmed by Panther Fusion system (31 Ct) using ZIKV primers and probes (ref 001 K-05694) and positive control (ref 001 K-05619) provided by the European Virus Archive-Marseille (EVAM, https://evam.european-virus-archive.com/). The serum was negative for anti-ZIKV IgM and IgG using EUROIMMUN ELISA kits; unfortunately, a convalescent sample was not collected and therefore, seroconversion was not assessed. The strain was successfully isolated on Vero E6 cells and deposited in the European Virus Archive collection (EVA, https://www.european-virus-archive.com/, ref-SKU 001 V-06178). Using an unbiased Klenow-based approach on the Illumina next-generation sequencing platform, we obtained a complete virus genome (GenBank accession number PV426612). To determine the geographical origin of the virus strain isolated in this study, we inferred the phylogenetic relationships between public near-complete virus sequences (>8500 nucleotides) available on GenBank as of March 2025 and the virus genome from the strain imported into France in August 2024, we found it belongs to the Asian lineage and is closely related to the sequence from the ZIKV infection imported from Seychelles into Italy in April of the same year (Figure 1).²

Figure 1.

Situation of the patient sample (France ex Seychelles_2024-08-01) among ZIKV sequences sampled globally. Phylogeny of ZIKV species estimated using a maximum likelihood approach under a GTR + F + R5 nucleotide substitution model implemented in IQ-TREE2. Statistical support for tree nodes and branches was estimated using ultrafast bootstrap approximation (UFBoot2, 1000 replicates).

Given the travel history, the rapid onset of symptoms after the patient’s return and the results of the phylogenetic analysis, it is likely that the ZIKV infection was acquired in Seychelles; moreover, no autochthonous ZIKV cases were recorded in metropolitan France in 2024. In addition to the case imported in Italy in April, the UK Government also reported a ZIKV infection from a returning traveller from Seychelles, having occurred between January and June 2024 (specific travel dates are not provided).³ Furthermore, between early August and mid-September, sequences from the Asian lineage of ZIKV and closely related to those from Seychelles were detected in Lamu Island, off the coast of Kenya (Figure 1).⁴ These recent detections constitute the first evidence of ZIKV circulation in the western Indian Ocean region, indicating active transmission throughout much of 2024, at least until September. So far, Seychelles and neighbouring islands-including La Réunion, Madagascar, Comoros, Mauritius and Mayotte-have been spared from ZIKV circulation, despite the presence of suitable conditions, and are considered at high risk for ZIKV outbreaks.⁵ Recent vector studies have shown that Aedes (Ae.) aegypti and Ae. albopictus mosquitoes from La Réunion are poorly competent for ZIKV Asian strains, while ZIKV African strains were efficiently transmitted.^6,7 In Seychelles, Ae. albopictus is the predominant mosquito species, with Ae. aegypti present at lower densities;⁸ both species have previously been implicated as vectors of chikungunya and dengue virus in Seychelles.^9,10 However, vector competence studies for ZIKV have not yet been conducted.

As a popular tourist destination, it is essential to strengthen surveillance in the Seychelles and neighbouring regions, as viremic travellers may introduce the virus into other areas with established populations of Ae. aegypti and Ae. albopictus. Clinicians should be aware of the risk of ZIKV infection in travellers returning from the Seychelles Islands.

Funding

This work was supported by the ARBOGEN project, funded by the MSDAVENIR Foundation. The activity of the National Reference Centers is supported by the National Public Health Agency (Santé Publique France, SPF). The activity of the UVE is supported by its supervising institutional bodies (Aix-Marseille Université, Università di Corsica, Institut national de la santé et de la recherche médicale, Institut de recherche pour le développement, Institut de Recherche Biomédicale des Armées).

Author contribution

Laura Pezzi (Conceptualization [equal], Data curation [equal], Formal analysis [equal], Investigation [equal], Methodology [equal], Project administration [equal], Resources [equal], Validation [equal], Writing—original draft [equal], Writing—review & editing [equal]), Nazli Ayhan (Data curation [equal], Formal analysis [equal], Investigation [equal], Methodology [equal], Resources [equal], Validation [equal], Writing—original draft [equal], Writing—review & editing [equal]), Justine Brulé (Investigation [equal], Methodology [equal], Resources [equal], Validation [equal], Writing—review & editing [equal]), Guillaume A Durand (Investigation [equal], Resources [equal], Validation [equal], Writing—review & editing [equal]), Gilda Grard (Investigation [equal], Resources [equal], Supervision [equal], Validation [equal], Writing—review & editing [equal]), Xavier De Lamballerie (Conceptualization [equal], Funding acquisition [equal], Investigation [equal], Methodology [equal], Project administration [equal], Resources [equal], Validation [equal], Writing—review & editing [equal]), and Raphaëlle Klitting (Conceptualization [equal], Data curation [equal], Formal analysis [equal], Funding acquisition [equal], Investigation [equal], Methodology [equal], Project administration [equal], Resources [equal], Supervision [equal], Validation [equal], Writing—original draft [equal], Writing—review & editing [equal])

Conflict of interest: Authors declare no conflict of interest.

Ethical statement

This study was part of the national public health surveillance programme of the National Reference Centre (NRC) for Arboviruses supervised by the National Public Health Agency (Santé Publique France, SPF). Therefore, as an epidemiological record, consultation with an ethics committee was not required. Samples transferred to the NRC are submitted with a form that includes the patient’s consent (non-opposition clause).

Data availability

Data (clinical features and laboratory results) underlying the findings reported here will be made available immediately following publication. Requests should be directed to the corresponding author. Genomic sequence is publicly available on GenBank under accession number PV426612.