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. 2023 Nov;28(48):2300258.
doi: 10.2807/1560-7917.ES.2023.28.48.2300258.

Ecological and clinical evidence of the establishment of West Nile virus in a large urban area in Europe, Berlin, Germany, 2021 to 2022

Claudia Ruscher  1 , Corinna Patzina-Mehling  2 , Julia Melchert  3   2 , Selina L Graff  2 , Sarah E McFarland  1 , Christian Hieke  2 , Anne Kopp  2 , Anita Prasser  1 , Torsten Tonn  4 , Michael Schmidt  4 , Caroline Isner  5 , Christian Drosten  3   2 , Dirk Werber  1 , Victor M Corman  6   3   2 , Sandra Junglen  2
Affiliations

Ecological and clinical evidence of the establishment of West Nile virus in a large urban area in Europe, Berlin, Germany, 2021 to 2022

Claudia Ruscher et al. Euro Surveill. 2023 Nov.

Abstract

BackgroundWest Nile virus (WNV), found in Berlin in birds since 2018 and humans since 2019, is a mosquito-borne virus that can manifest in humans as West Nile fever (WNF) or neuroinvasive disease (WNND). However, human WNV infections and associated disease are likely underdiagnosed.AimWe aimed to identify and genetically characterise WNV infections in humans and mosquitoes in Berlin.MethodsWe investigated acute WNV infection cases reported to the State Office for Health and Social Affairs Berlin in 2021 and analysed cerebrospinal fluid (CSF) samples from patients with encephalitis of unknown aetiology (n = 489) for the presence of WNV. Mosquitoes were trapped at identified potential exposure sites of cases and examined for WNV infection.ResultsWest Nile virus was isolated and sequenced from a blood donor with WNF, a symptomatic patient with WNND and a WNND case retrospectively identified from testing CSF. All cases occurred in 2021 and had no history of travel 14 days prior to symptom onset (incubation period of the disease). We detected WNV in Culex pipiens mosquitoes sampled at the exposure site of one case in 2021, and in 2022. Genome analyses revealed a monophyletic Berlin-specific virus clade in which two enzootic mosquito-associated variants can be delineated based on tree topology and presence of single nucleotide variants. Both variants have highly identical counterparts in human cases indicating local acquisition of infection.ConclusionOur study provides evidence that autochthonous WNV lineage 2 infections occurred in Berlin and the virus has established an endemic maintenance cycle.

Keywords: Berlin; West Nile virus; arbovirus; mosquito; mosquito-borne disease.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Detailed information on the detection and sequencing of West Nile virus showing (A) mosquito trapping sites in Berlina, (B) phylogeny of the Berlin cladeb and (C) scheme of the West Nile virus genome showing the Berlin variantsc, Berlin, Germany, 2021–2022
Figure 2
Figure 2
Phylogenetic relationship of the complete coding region of West Nile virus lineage 2 strains
Figure 3
Figure 3
Comparative growth curves of two West Nile virus isolates from a human and a mosquito on a primate cell line, Berlin, Germany, 2021–2022
See this image and copyright information in PMC

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