Usutu virus (USUV) is a flavivirus (Flaviviridae: Flavivirus) of an African origin transmitted among its natural hosts (diverse species of birds) by mosquitoes. The virus was introduced multiple times to Europe where it caused mortality of blackbirds (Turdus merula) and certain other susceptible species of birds. In this study, we report detection of USUV RNA in blackbirds, Culex pipiens and Cx. modestus mosquitoes in the Czech Republic, and isolation of 10 new Czech USUV strains from carcasses of blackbirds in cell culture. Multiple lineages (Europe 1, 2 and Africa 3) of USUV were found in blackbirds and mosquitoes in the southeastern part of the country. A single USUV lineage (Europe 3) was found in Prague and was likely associated with increased mortalities in the local blackbird population seen in this area in 2018. USUV genomic RNA (lineage Europe 2) was detected in a pool of Cx. pipiens mosquitoes from South Bohemia (southern part of the country), where no major mortality of birds has been reported so far, and no flavivirus RNA has been found in randomly sampled cadavers of blackbirds. The obtained data contributes to our knowledge about USUV genetic variability, distribution and spread in Central Europe.

CEITEC University of Veterinary and Pharmaceutical Sciences 61242 Brno Czech Republic

Centre for Epidemiology and Microbiology National Institute of Public Health 10000 Prague Czech Republic

Department of Parasitology Faculty of Science Charles University 12800 Prague Czech Republic

Department of Pathology and Parasitology Faculty of Veterinary Medicine University of Veterinary and Pharmaceutical Sciences 61242 Brno Czech Republic

Department of Virology Veterinary Research Institute 62100 Brno Czech Republic

Faculty of Science University of South Bohemia 37005 Ceske Budejovice Czech Republic

Institute of Parasitology Biology Centre Czech Academy of Sciences 37005 Ceske Budejovice Czech Republic

Institute of Vertebrate Biology Czech Academy of Sciences 60365 Brno Czech Republic

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Detection of Usutu virus in a house martin bug Oeciacus hirundinis (Hemiptera: Cimicidae): implications for virus overwintering in a temperate zone

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

Mosquito surveillance of West Nile and Usutu viruses in four territorial units of Slovakia and description of a confirmed autochthonous human case of West Nile fever, 2018 to 2019

Hedgehogs, Squirrels, and Blackbirds as Sentinel Hosts for Active Surveillance of Borrelia miyamotoi and Borrelia burgdorferi Complex in Urban and Rural Environments