West Nile Virus Infections in Germany: Update 2022–2024

Introduction: West Nile virus (WNV) is an arthropod-borne virus (arbovirus). It circulates in an enzootic cycle between ornithophilic mosquitoes as vectors and different avian species as reservoir hosts and/or for amplification but humans can be infected as accidental hosts. Since 2019, autochthonous mosquito-borne WNV infections in humans were reported in Germany indicating a continuous circulation in the affected areas. The animal and human infections were initially restricted to Central-East Germany in the first years. This article provides an update to the WNV epidemiology in Germany from 2022 to 2024. Methods: Analysis was based on surveillance data and confirmatory testing for human and animal cases of WNV in Germany from 2022 to 2024. Results: Since 2022, a slight annual spread became visible, which intensified in 2024 and caused numerous infections in northwest Germany, particularly among animals. Altogether, 80 confirmed human WNV infections were identified in 2022-2024, mostly among blood donors. Transfusion safety is maintained by donor deferral or testing of donations using nucleic acid amplification techniques (NAT) after a stay in an affected area. The vast majority of blood establishments test all donations during the transmission season in Germany from June to the end of November. In this way, roughly 2.2 million donations are screened annually, by that contributing significantly to WNV surveillance. Conclusion: Confirmation of initially reactive screening tests is still a challenge as other flaviviruses, especially Usutu virus, are co-circulating. Specific NAT or next-generation sequencing are necessary for discrimination. To fully understand the WNV epidemic, combined results of human and veterinary surveillance including results of sequencing are needed. A One health approach is essential to identify affected areas and to ensure transfusion safety and public health.