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

Abstract

Background West 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. Aim We aimed to identify and genetically characterise WNV infections in humans and mosquitoes in Berlin. Methods We 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. Results West 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. Conclusion Our study provides evidence that autochthonous WNV lineage 2 infections occurred in Berlin and the virus has established an endemic maintenance cycle.

Winged Threat on the Offensive: A Literature Review Due to the First Identification of Aedes japonicus in Poland

“…Currently, the northern range of West Nile virus occurrence is Germany, where WNV has been detected since 2018 both in birds and equines, as well as in humans [98]. Its presence in other neighboring countries, e.g., the Czech Republic [98], leads to the assumption that it also occurs in Poland, although no local outbreaks of the disease have been detected here so far. Although West Nile fever outbreaks occur with unpredictable frequency and location, there has been a gradual expansion of the disease's geographical range in Europe.…”

“…In 2023, EU/EEA countries reported 707 cases of WNV infection in humans, mainly in Italy, Greece, Romania, France, and Hungary, but cases were also detected in Spain, Germany, Croatia, and Cyprus [97]. Currently, the northern range of West Nile virus occurrence is Germany, where WNV has been detected since 2018 both in birds and equines, as well as in humans [98]. Its presence in other neighboring countries, e.g., the Czech Republic [98], leads to the assumption that it also occurs in Poland, although no local outbreaks of the disease have been detected here so far.…”