Targeted surveillance reveals native and invasive mosquito species infected with Usutu virus

Jeremy V. Camp,Norbert Nowotny,Jolanta Kolodziejek

doi:10.1186/s13071-019-3316-z

Abstract

BackgroundThe emergence of Usutu virus (USUV) in Europe was first reported in Austria, 2001, and the virus has since spread to many European countries. Initial outbreaks are marked by a mass die-off of European blackbirds (Turdus merula) and other bird species. During outbreaks, the virus has been detected in pools of Culex pipiens mosquitoes, and these mosquitoes are probably the most important enzootic vectors. Beginning in 2017, a second wave of blackbird deaths associated with USUV was observed in eastern Austria; the affected areas expanded to the Austrian federal states of Styria in the south and to Upper Austria in the west in 2018. We sampled the potential vector population at selected sites of bird deaths in 2018 in order to identify infected mosquitoes.ResultsWe detected USUV RNA in 16 out of 19 pools of Cx. pipiens/Cx. torrentium mosquitoes at sites of USUV-linked blackbird mortality in Linz and Graz, Austria. A disseminated virus infection was detected in individuals from selected pools, suggesting that Cx. pipiens form pipiens was the principal vector. In addition to a high rate of infected Cx. pipiens collected from Graz, a disseminated virus infection was detected in a pool of Aedes japonicus japonicus.ConclusionsWe show herein that naturally-infected mosquitoes at foci of USUV activity are primarily Cx. pipiens form pipiens. In addition, we report the first natural infection of Ae. j. japonicus with USUV, suggesting that it may be involved in the epizootic transmission of USUV in Europe. Ae. j. japonicus is an invasive mosquito whose range is expanding in Europe.

Highlights

The emergence of Usutu virus (USUV) in Europe was first reported in Austria, 2001, and the virus has since spread to many European countries
In Graz, two nights of trapping resulted in 315 Cx. pipiens/Cx. torrentium (8 from the light trap, 2 of which were gravid, and all except for 32 of the remaining specimens collected in the gravid trap were gravid), 17 Ae. j. japonicus (10 from the light trap, and 2 of 7 from the gravid trap were gravid), three Aedes vexans (Meigen, 1830) captured in the light trap, and one An. maculipennis (Meigen, 1818) captured in the light trap (Table 1)
Two of the three pools containing seven and 15 Cx. pipiens/Cx. torrentium mosquitoes, respectively, from Linz were positive for USUV nucleic acid (Table 1)

Summary

Introduction

The emergence of Usutu virus (USUV) in Europe was first reported in Austria, 2001, and the virus has since spread to many European countries. Initial outbreaks are marked by a mass die-off of European blackbirds (Turdus merula) and other bird species. In 2001, USUV was first identified in Austria, associated with a large die-off of Eurasian (or common) blackbirds (Turdus merula Linnaeus, 1758) [2], the initial emergence in Europe may have been earlier [3]. The virus spread to many European countries and is typically associated with the death of certain species of native birds, mainly blackbirds [4,5,6,7]. The identification of USUV nucleic acid in field-captured mosquito pools suggests that Culex pipiens Linnaeus, 1758 is the principal vector in Europe [16]. Experimental vector competence studies have demonstrated that European Cx. pipiens form pipiens populations are

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