First Evidence of West Nile Virus Overwintering in Mosquitoes in Germany.

Helge Kampen,Birke Andrea Tews,Doreen Werner

doi:10.3390/v13122463

Helge Kampen, Birke Andrea Tews + Show 1 more

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https://doi.org/10.3390/v13122463

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Abstract

Mosquitoes collected from mid-December 2020 to early March 2021 from hibernacula in northeastern Germany, a region of West Nile virus (WNV) activity since 2018, were examined for WNV-RNA. Among the 6101 mosquitoes tested in 722 pools of up to 12 specimens, one pool of 10 Culex pipiens complex mosquitoes collected in early March 2021 in the cellar of a medieval castle in Rosslau, federal state of Saxony-Anhalt, tested positive. Subsequent mosquito DNA analysis produced Culex pipiens biotype pipiens. The pool homogenate remaining after nucleic acid extraction failed to grow the virus on Vero and C6/36 cells. Sequencing of the viral NS2B-NS3 coding region, however, demonstrated high homology with virus strains previously collected in Germany, e.g., from humans, birds, and mosquitoes, which have been designated the East German WNV clade. The finding confirms the expectation that WNV can overwinter in mosquitoes in Germany, facilitating an early start to the natural transmission season in the subsequent year. On the other hand, the calculated low infection prevalence of 0.016–0.20%, depending on whether one or twelve of the mosquitoes in the positive pool was/were infected, indicates a slow epidemic progress and mirrors the still-hypoendemic situation in Germany. In any case, local overwintering of the virus in mosquitoes suggests its long-term persistence and an enduring public health issue.

Highlights

West Nile virus (WNV) is a flavivirus pathogenic to humans, horses, and birds
The mosquitoes were assigned to five taxa: An. maculipennis complex (69 specimens, 21 pools), Cs. annulata (791 specimens, 162 pools), Cx. hortensis/territans (23 specimens, 8 pools), Cx. pipiens complex (5217 specimens, 530 pools), and Uranotaenia unguiculata (1 specimen, 1 pool) (Table S1)
Among all the pools tested for viruses, one single pool collected on 9 March 2021 in a dungeon of a medieval castle in Rosslau, federal state of Brandenburg (Figure 1), was WNV-RNA-positive according to NS5 and NS2B-NS3 gene PCR and sequencing

Summary

Introduction

West Nile virus (WNV) is a flavivirus (family Flaviviridae) pathogenic to humans, horses, and birds. During the large European West Nile virus epidemic in 2018, which affected 15 countries with 2083 human infections, including 166 fatal ones, and 285 equine outbreaks in EU member states [6,7], the virus emerged for the first time in Germany [8]. In both 2019 and 2020, case numbers increased in Germany, with the first human case diagnosed in 2019 and the first fatal human case occurring in 2020 [9,10]. Confirmed cases were determined in northeastern Germany, notably in areas of Berlin and Leipzig [11]

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