The 2022 West Nile Virus Season in Greece; A Quite Intense Season.

Since 2010, the West Nile virus (WNV) has been established in Greece. We describe the epidemiology of diagnosed human WNV infections in Greece with a focus on the 2022 season. During the transmission period, clinicians were sending samples from suspected cases for testing. Active laboratory-based surveillance was performed with immediate notification of diagnosed cases. We collected clinical information and interviewed patients on a timely basis to identify their place of exposure. Besides serological and molecular diagnostic methods, next-generation sequencing was also performed. In 2022, 286 cases of WNV infection were diagnosed, including 278 symptomatic cases and 184 (64%) cases with neuroinvasive disease (WNND); 33 patients died. This was the third most intense season concerning the number of WNND cases, following 2018 and 2010. Most (96%) cases were recorded in two regions, in northern and central Greece. The virus strain was a variant of previous years, clustering into the Central European subclade of WNV lineage 2. The 2022 WNV season was quite intense in Greece. The prompt diagnosis and investigation of cases are considered pivotal for the timely response, while the availability of whole genome sequences enables studies on the molecular epidemiology of the disease.

West Nile fever upsurge in a Greek regional unit, 2020.

During the 2020 West Nile virus (WNV) transmission season, Greece was the most affected EU Member State. More than one third of human cases occurred in Serres regional unit in northern Greece, which is characterized by the presence of a major wetland (Kerkini lake and Strimon river). A total of 2809 Culex pipiens mosquitoes collected in Serres were grouped into 70 pools and tested for WNV. Ten (14.3%) pools were found positive, and all WNV sequences belonged to the Central European subclade of WNV lineage 2. The first human case occurred in a village nearby the lake, and all following cases occurred across the connected river and its tributaries. Similar distribution presented the sites where WNV-positive mosquitoes were detected. The number of Culex spp. mosquitoes per trap per night was higher in 2020 than in previous years (2017-2019). The spatial and temporal distribution of human cases and WNV-positive mosquitoes in 2020 in Serres regional unit suggest that the upsurge of the virus circulation was probably related with factors that affected the ecosystem of the wetland.