Citation: Coroian, M.; Mihalca, A.D.; Dobler, G.; Euringer, K.; Girl, P.; Bors , an, S.-D.; Kalmár, Z.; Tincut , a Briciu, V.; Flonta, M.; Topan, A.; et al. Seroprevalence Rates against West Nile, Usutu, and Tick-Borne Encephalitis Viruses in Blood-Donors from North-Western Romania. Int. J. Environ. Res. Public Health 2022, 19, 8182. https://doi.org/10.3390/ ijerph19138182 Academic Editors: Andrea Trevisan, Chiara Bertoncello and Marco Fonzo Received: 10 May 2022 Accepted: 1 July 2022 Published: 4 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). International Journal of Environmental Research and Public Health Article Seroprevalence Rates against West Nile, Usutu, and Tick-Borne Encephalitis Viruses in Blood-Donors from North-Western Romania Mircea Coroian 1,2 , Andrei Daniel Mihalca 1 , Gerhard Dobler 3,4 , Kathrin Euringer 3,4 , Philipp Girl 3,4 , Silvia-Diana Bors , an 1 , Zsuzsa Kalmár 2,5, *, Violeta Tincut , a Briciu 2,6 , Mirela Flonta 6 , Adriana Topan 2 , Amanda Lelia Rădulescu 2 , Andrei Ungur 7 and Mihaela Sorina Lups , e 2,6 1 Department of Parasitology and Parasitic Diseases, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, 400372 Cluj-Napoca, Romania; mircea.coroian@usamvcluj.ro (M.C.); amihalca@usamvcluj.ro (A.D.M.); silvia.borsan@usamvcluj.ro (S.-D.B.) 2 Department of Infectious Diseases, University of Medicine and Pharmacy “Iuliu Hat , ieganu” Cluj-Napoca, 400012 Cluj-Napoca, Romania; briciu.tincuta@umfcluj.ro (V.T.B.); topanadriana@yahoo.com (A.T.); aradulescu@umfcluj.ro (A.L.R.); mihaela.lupse@yahoo.com (M.S.L.) 3 Bundeswehr Institute of Microbiology, 85748 Munich, Germany; gerharddobler@bundeswehr.org (G.D.); kathrineuringer@bundeswehr.org (K.E.); philipp.girl@bundeswehr.org (P.G.) 4 German Centre for Infection Research (DZIF), 85748 Munich, Germany 5 Department of Microbiology, Immunology and Epidemiology, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, 400372 Cluj-Napoca, Romania 6 Hospital for Infectious Diseases, 400348 Cluj-Napoca, Romania; m.flonta@yahoo.com 7 Department of Pathology, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, 400372 Cluj-Napoca, Romania; andrei.ungur@usamvcluj.ro * Correspondence: zsuzsa.kalmar@usamvcluj.ro Abstract: Introduction: West Nile virus (WNV), Usutu virus (USUV), and the tick-borne encephalitis virus (TBEV) are all arboviruses belonging to Flaviviridae family. All are characterized by vectorial transmission and sometimes associated with neuroinvasive infections. The circulation of these viruses is considered endemic in parts of Europe, with human cases reported in many countries. Among hosts, the viruses are vectored by hematophagous arthropods, such as mosquitoes (WNV, USUV) and ticks (TBEV). Considering the currently outdated knowledge regarding the epidemiology of these viruses in Romania, the aim of our study was to assess the seroprevalence rates of WNV, USUV, and TBEV among healthy blood donors in north-western Romania. Methods: Human blood samples from healthy donors were collected between November 2019 and February 2020 in six counties from the north-western region of Romania. The samples were serologically tested by ELISA and serum neutralization test. Results: Overall, we obtained a seroprevalence of 3.17% for WNV, 0.08% for TBEV, and 0% for USUV. Conclusion: Despite the low seroprevalence of WNV, USUV, and TBEV in our study, we highlight the need for continuous nationwide vector and disease surveillance and implementation of control measures. Further research is required for an optimal overview of the epidemiological status of the Romanian population regarding these flaviviruses together with countrywide awareness campaigns. Keywords: arboviruses; public health; tick-borne encephalitis virus; Usutu virus; vector-borne diseases; West Nile virus 1. Introduction West Nile virus (WNV), Usutu virus (USUV), and the tick-borne encephalitis virus (TBEV) are all arboviruses belonging to Flaviviridae family, characterized by vectorial transmission and sometimes associated with neuroinvasive infections. The circulation of these viruses is considered endemic in some parts of Europe, with cases reported in many Int. J. Environ. Res. Public Health 2022, 19, 8182. https://doi.org/10.3390/ijerph19138182 https://www.mdpi.com/journal/ijerph