Screening of Mosquitoes for West Nile Virus and Usutu Virus in Croatia, 2015-2020.

Ana Klobucar,Ivan Toplak,Vladimir Savic,Tatjana Vilibic-Cavlek,Urska Kuhar,Josip Madic,Suncica Petrinic,Marcela Curman Posavec

doi:10.3390/tropicalmed6020045

Abstract

In the period from 2015 to 2020, an entomological survey for the presence of West Nile virus (WNV) and Usutu virus (USUV) in mosquitoes was performed in northwestern Croatia. A total of 20,363 mosquitoes were sampled in the City of Zagreb and Međimurje county, grouped in 899 pools and tested by real-time RT-PCR for WNV and USUV RNA. All pools were negative for WNV while one pool each from 2016 (Aedes albopictus), 2017 (Culex pipiens complex), 2018 (Cx. pipiens complex), and 2019 (Cx. pipiens complex), respectively, was positive for USUV. The 2018 and 2019 positive pools shared 99.31% nucleotide homology within the USUV NS5 gene and both clustered within USUV Europe 2 lineage. The next-generation sequencing of one mosquito pool (Cx. pipiens complex) collected in 2018 in Zagreb confirmed the presence of USUV and revealed several dsDNA and ssRNA viruses of insect, bacterial and mammalian origin.

Highlights

West Nile virus (WNV) and Usutu virus (USUV) are mosquito-borne arboviruses of the genus Flavivirus, family Flaviviridae
Out of a total of 72 mosquitoes from Medimurje County, 52.8% belong to Cx. pipiens complex, followed by Ae. vexans (41.7%) and Oc. sticticus (5.5%) (Table 2)
Human USUV infections were not reported at that time; one pool of Cx. pipiens complex mosquitoes collected in north-west Croatia (Prelog, Medimurje County) tested positive for USUV RNA

Summary

Introduction

West Nile virus (WNV) and Usutu virus (USUV) are mosquito-borne arboviruses of the genus Flavivirus, family Flaviviridae. In Europe, both viruses have been detected in humans, horses, mosquitoes, and birds [1,2]. WNV is sustained in an enzootic cycle between birds and mosquitoes while humans and horses represent “dead-end” hosts. Numerous bird species are competent amplifier hosts for WNV, and mosquitoes of the genus Culex are the main vectors [3]. WNV has been responsible for sporadic outbreaks in Mediterranean countries since 1960s [4]. The occurrence of outbreaks in many European countries has significantly increased [1,5]. The highest number of WNV infections in Europe was recorded in 2018. Number of cases were seven times higher than in 2017 (1605 versus 212) and exceeded all cases reported between 2011 and 2017 [6]

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Conclusion