West Nile Virus Lineage 2 Spreads Westwards in Europe and Overwinters in North-Eastern Spain (2017–2020)

Pilar Aguilera-Sepúlveda,Francisco Llorente,Jovita Fernández-Pinero,Alba Solé,Núria Busquets,Sebastián Napp,Carlos Solano-Manrique,Rafael Molina-López,Miguel Ángel Jiménez-Clavero,Elena Obón

doi:10.3390/v14030569

Abstract

West Nile virus lineage 2 (WNV-L2) emerged in Europe in 2004; since then, it has spread across the continent, causing outbreaks in humans and animals. During 2017 and 2020, WNV-L2 was detected and isolated from four northern goshawks in two provinces of Catalonia (north-eastern Spain). In order to characterise the first Spanish WNV-L2 isolates and elucidate the potential overwintering of the virus in this Mediterranean region, complete genome sequencing, phylogenetic analyses, and a study of phenotypic characterisation were performed. Our results showed that these Spanish isolates belonged to the central-southern WNV-L2 clade. In more detail, they were related to the Lombardy cluster that emerged in Italy in 2013 and has been able to spread westwards, causing outbreaks in France (2018) and Spain (2017 and 2020). Phenotypic characterisation performed in vitro showed that these isolates presented characteristics corresponding to strains of moderate to high virulence. All these findings evidence that these WNV-L2 strains have been able to circulate and overwinter in the region, and are pathogenic, at least in northern goshawks, which seem to be very susceptible to WNV infection and may be good indicators of WNV-L2 circulation. Due to the increasing number of human and animal cases in Europe in the last years, this zoonotic flavivirus should be kept under extensive surveillance, following a One-Health approach.

Highlights

West Nile virus (WNV) is one of the most widespread zoonotic arboviruses in the world, as it is present in Africa, Europe, the MiddleEast, Asia, and the New World [1]
Within the surveillance program for WNV implemented in Catalonia, birds found dead or that died at the Wildlife Rehabilitation Centres (WRC) had their heads sent to IRTA-CReSA to be diagnosed for WNV in encephalon samples
Further analysis of a partial sequence of the NS5 gene indicated that all the positive samples belonged to West Nile virus lineage 2 (WNV-L2)

Summary

Introduction

West Nile virus (WNV) (genus Flavivirus, family Flaviviridae) is one of the most widespread zoonotic arboviruses in the world, as it is present in Africa, Europe, the Middle. It circulates in an enzootic cycle where mosquitoes (mainly Culex spp.) act as vectors and birds are the reservoir hosts. Humans and horses can be infected and may develop a neurologic disease; they are considered dead-end hosts, as the viraemia resulting from the infection is insufficient to infect a new vector. Over 80% of WNV infections in humans are asymptomatic and the most prevalent clinical manifestation is West Nile fever (WNF) [3]. WNV may cause encephalitis or encephalomyelitis that may provoke clinical signs such as ataxia, incoordination, weakness, muscle fasciculation, and cranial nerve deficits

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