West Nile virus lineage 2 (WNV-2) was mainly
confined to sub-Saharan Africa until the early
2000s, when it was identified for the first time in
Central Europe causing outbreaks of human and animal
The aim of this new study was to reconstruct the
origin and dispersion of WNV-2 in Central Europe and
Italy on a phylodynamic and phylogeographical basis.
To this aim, discrete and continuous space
phylogeographical models were applied to a total of
33 newly characterised full-length viral genomes
obtained from mosquitoes, birds and humans in
Northern Italy in the years 2013–2015 aligned with
64 complete sequences isolated mainly in Europe.
The European isolates segregated into two highly
significant clades: a small one including three
sequences and a large clade including the majority
of isolates obtained in Central Europe since 2004.
Discrete phylogeographical analysis showed that the
most probable location of the root of the largest
European clade was in Hungary a mean 12.78 years
The European clade bifurcated into two highly
supported subclades: one including most of the
Central/East European isolates and the other
encompassing all of the isolates obtained in Greece.
The continuous space phylogeographical analysis of
the Italian clade showed that WNV-2 entered Italy in
about 2008, probably by crossing the Adriatic sea
and reaching a central area of the Po Valley.
The epidemic then spread simultaneously eastward, to
reach the region of the Po delta in 2013, and
westward to the border area between Lombardy and
Piedmont in 2014; later, the western strain changed
direction southward, and reached the central area of
the Po valley once again in 2015.
Over a period of about seven years, the virus spread
all over an area of northern Italy by following the
Po river and its main tributaries.
For more information
Zehender G, Veo C, Ebranati E, Carta V, Rovida F,
Percivalle E, et al. (2017)
Reconstructing the recent West Nile virus lineage 2
epidemic in Europe and Italy using discrete and
continuous phylogeography. PLoS ONE 12(7): e0179679.
Università degli Studi di Milano
Scienze biomediche e cliniche 'L. Sacco'