West Nile Virus Lineage 1 in Italy: Newly Introduced or a Re-Occurrence of a Previously Circulating Strain?

Giulia Mencattelli,Federica Monaco,Shadia Berjaoui,Federica Iapaolo,Giovanna Fusco,Valentina Curini,Giovanni Savini,Claudio De Martinis,Ottavio Portanti,Annapaola Rizzoli,Roberto Rosà,Elisabetta Di Felice,Andrea Polci,Annapia Di Gennaro

doi:10.3390/v14010064

Abstract

In Italy, West Nile virus (WNV) appeared for the first time in the Tuscany region in 1998. After 10 years of absence, it re-appeared in the areas surrounding the Po River delta, affecting eight provinces in three regions. Thereafter, WNV epidemics caused by genetically divergent isolates have been documented every year in the country. Since 2018, only WNV Lineage 2 has been reported in the Italian territory. In October 2020, WNV Lineage 1 (WNV-L1) re-emerged in Italy, in the Campania region. This is the first occurrence of WNV-L1 detection in the Italian territory since 2017. WNV was detected in the internal organs of a goshawk (Accipiter gentilis) and a kestrel (Falco tinnunculus). The RNA extracted in the goshawk tissue samples was sequenced, and a Bayesian phylogenetic analysis was performed by a maximum-likelihood tree. Genome analysis, conducted on the goshawk WNV complete genome sequence, indicates that the strain belongs to the WNV-L1 Western-Mediterranean (WMed) cluster. Moreover, a close phylogenetic similarity is observed between the goshawk strain, the 2008–2011 group of Italian sequences, and European strains belonging to the Wmed cluster. Our results evidence the possibility of both a new re-introduction or unnoticed silent circulation in Italy, and the strong importance of keeping the WNV surveillance system in the Italian territory active.

Highlights

Publisher’s Note: MDPI stays neutralWest Nile virus (WNV) is a mosquito borne single-stranded RNA virus, a member of the Japanese encephalitis (JE) serocomplex belonging to the genus Flavivirus within the Flaviviridae family [1]
We describe the two cases, and characterize by whole genome sequencing (WGS) and phylogenetic analysis the WNV lineage 1 (WNV-L1) responsible for the goshawk infection
This paper reports the first evidence of WNV-L1 strain circulation in the Campania region, Italy

Summary

Introduction

Publisher’s Note: MDPI stays neutralWest Nile virus (WNV) is a mosquito borne single-stranded RNA virus, a member of the Japanese encephalitis (JE) serocomplex belonging to the genus Flavivirus within the Flaviviridae family [1]. WNV is maintained in nature through an endemic cycle which involves mosquitoes (Diptera; Culicidae) as vectors, and birds as reservoir hosts [2]. Humans and horses are considered “dead-end” hosts: they may develop disease; they are not able to infect vectors, and maintain the virus in the environment [3]. Lineages 1 and 2, often associated with cases of encephalitis in humans and horses, are by far those most widespread in Europe and the Mediterranean basin [5,6,7,8]. In Europe, WNV lineage 1 (WNV-L1) circulation was first evidenced in the 1960s in France, Portugal, and Cyprus [8,9,10]. Cases associated to WNV-L1 infection were reported in humans and horses in North African, Western, and Eastern

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