BACKGROUND: West Nile virus (WNV) is currently the most important mosquito-borne pathogen spreading in Europe. Data on overwintering of WNV in mosquitoes are crucial for understanding WNV circulation in Europe; nonetheless, such data were not available so far. RESULTS: A total of 28,287 hibernating mosquitoes [27,872 Culex pipiens, 73 Anopheles maculipennis (sensu lato), and 342 Culiseta annulata], caught in February or March between 2011 and 2017 in a WNV-endemic region of South Moravia, Czech Republic, were screened for the presence of WNV RNA. No WNV positive pools were found from 2011 to 2016, while lineage 2 WNV RNA was detected in three pools of Culex pipens mosquitoes collected in 2017 at two study sites. CONCLUSIONS: To the best of our knowledge, this is the first record of WNV RNA in overwintering mosquitoes in Europe. The data support the hypothesis of WNV persistence in mosquitoes throughout the winter season in Europe.

Department of Basic Medical Sciences College of Medicine Mohammed Bin Rashid University of Medicine and Health Sciences Dubai Healthcare City Dubai United Arab Emirates

Department of Experimental Biology Masaryk University Brno Czech Republic

Department of Microbiology and Infectious Diseases University of Veterinary Medicine Budapest Hungary

Francis Schaffner Consultancy Riehen Switzerland

Institute of Macromolecular Chemistry v v i Czech Academy of Sciences Praha Czech Republic

Institute of Vertebrate Biology Czech Academy of Sciences v v i Brno Czech Republic

Institute of Virology University of Veterinary Medicine Vienna Austria

National Centre for Vector Entomology Institute of Parasitology Vetsuisse Faculty University of Zurich Zurich Switzerland

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History of Arbovirus Research in the Czech Republic

First Autochthonous West Nile Lineage 2 and Usutu Virus Infections in Humans, July to October 2018, Czech Republic