BackgroundDespite the known circulation of West Nile virus (WNV) and Usutu virus (USUV) in Slovakia, no formal entomological surveillance programme has been established there thus far.AimTo conduct contemporaneous surveillance of WNV and USUV in different areas of Slovakia and to assess the geographical spread of these viruses through mosquito vectors. The first autochthonous human WNV infection in the country is also described.MethodsMosquitoes were trapped in four Slovak territorial units in 2018 and 2019. Species were characterised morphologically and mosquito pools screened for WNV and USUV by real-time reverse-transcription PCRs. In pools with any of the two viruses detected, presence of pipiens complex group mosquitoes was verified using molecular approaches.ResultsAltogether, 421 pools containing in total 4,508 mosquitoes were screened. Three pools tested positive for WNV and 16 for USUV. USUV was more prevalent than WNV, with a broader spectrum of vectors and was detected over a longer period (June-October vs August for WNV). The main vectors of both viruses were Culex pipiens sensu lato. Importantly, WNV and USUV were identified in a highly urbanised area of Bratislava city, Slovakias' capital city. Moreover, in early September 2019, a patient, who had been bitten by mosquitoes in south-western Slovakia and who had not travelled abroad, was laboratory-confirmed with WNV infection.ConclusionThe entomological survey results and case report increase current understanding of the WNV and USUV situation in Slovakia. They underline the importance of vector surveillance to assess public health risks posed by these viruses.

Institute of Animal Physiology Centre of Biosciences Slovak Academy of Sciences Košice Slovakia

Institute of Parasitology Slovak Academy of Sciences Košice Slovakia

Institute of Virology Biomedical Research Center Slovak Academy of Sciences Bratislava Slovakia

Research Station and Museum of TANAP Tatranská Lomnica Slovakia

School of Health Sciences Federation University Berwick Australia

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

The National Reference Centre for Arboviruses and Haemorrhagic Fevers of the Public Health Authority of the Slovak Republic Bratislava Slovakia

University of Veterinary Medicine and Pharmacy Košice Slovakia

Veterinary and Food Institute in Bratislava Bratislava Slovakia

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An unwanted companion reaches the country: the first record of the alien mosquito Aedes japonicus japonicus (Theobald, 1901) in Slovakia