West Nile Virus Surveillance in 2013 via Mosquito Screening in Northern Italy and the Influence of Weather on Virus Circulation.
West Nile virus (WNV) is a recently re-emerged health problem in Europe. In Italy, an increasing number of outbreaks of West Nile disease, with occurrences of human cases, have been reported since 2008. This is particularly true in northern Italy, where entomological surveillance systems have been implemented at a regional level. The aim of this study was to use, for the first time, all the entomological data collected in the five regions undergoing surveillance for WNV in northern Italy to characterize the viral circulation (at a spatial and temporal scale), identify potential mosquito vectors, and specify relationships between virus circulation and meteorological conditions. In 2013, 286 sites covering the entire Pianura Padana area were monitored. A total of 757,461 mosquitoes were sampled. Of these, 562,079 were tested by real-time PCR in 9,268 pools, of which 180 (1.9%) were positive for WNV. The largest part of the detected WNV sequences belonged to lineage II, demonstrating that, unlike those in the past, the 2013 outbreak was mainly sustained by this WNV lineage. This surveillance also detected the Usutu virus, a WNV-related flavivirus, in 241 (2.6%) pools. The WNV surveillance systems precisely identified the area affected by the virus and detected the viral circulation approximately two weeks before the occurrence of onset of human cases. Ninety percent of the sampled mosquitoes were Culex pipiens, and 178/180 WNV-positive pools were composed of only this species, suggesting this mosquito is the main WNV vector in northern Italy. A significantly higher abundance of the vector was recorded in the WNV circulation area, which was characterized by warmer and less rainy conditions and greater evapotranspiration compared to the rest of the Pianura Padana, suggesting that areas exposed to these conditions are more suitable for WNV circulation. This observation highlights warmer and less rainy conditions as factors able to enhance WNV circulation and cause virus spillover outside the sylvatic cycle.
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Mattia
M
Calzolari
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Alessandra
A
Pautasso
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Fabrizio
F
Montarsi
Centro Agricoltura Ambiente "G.Nicoli," Crevalcore (BO), Italy.
Alessandro
A
Albieri
Centro Agricoltura Ambiente "G.Nicoli," Crevalcore (BO), Italy.
Romeo
R
Bellini
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Paolo
P
Bonilauri
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Francesco
F
Defilippo
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Davide
D
Lelli
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Ana
A
Moreno
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Mario
M
Chiari
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Marco
M
Tamba
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Mariagrazia
M
Zanoni
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Giorgio
G
Varisco
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Silvia
S
Bertolini
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Paola
P
Modesto
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Maria Cristina
MC
Radaelli
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Barbara
B
Iulini
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Marino
M
Prearo
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Silvia
S
Ravagnan
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Stefania
S
Cazzin
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Paolo
P
Mulatti
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Isabella
I
Monne
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Lebana
L
Bonfanti
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Stefano
S
Marangon
Istituto Zooprofilattico Spermentale dell'Abruzzo e Molise, Teramo, Italy.
Maria
M
Goffredo
Istituto Zooprofilattico Spermentale dell'Abruzzo e Molise, Teramo, Italy.
Giovanni
G
Savini
Entostudio snc, Brugine (PD), Italy.
Simone
S
Martini
Istituto per le Piante da Legno e l'Ambiente S.p.A., Torino, Italy.
Andrea
A
Mosca
Regione Lombardia, Milano, Italy.
Marco
M
Farioli
Regione Lombardia, Milano, Italy.
Laura
L
Gemma Brenzoni
Regione Friuli Venezia-Giulia, Trieste, Italy.
Manlio
M
Palei
Regione Veneto, Venezia, Italy.
Francesca
F
Russo
Regione Emilia-Romagna, Bologna, Italy.
Silvano
S
Natalini
Regione Emilia-Romagna, Bologna, Italy.
Paola
P
Angelini
Istituto Zooprofilattico del Piemonte Liguria e Valle d'Aosta, Torino, Italy.
Cristina
C
Casalone
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Brescia, Italy.
Michele
M
Dottori
Istituto Zooprofilattico Sperimentale delle Venezie, Leganro (PD), Italy.
Gioia
G
Capelli
D000818:Animals; D003465:Culex / Q000821:virology*; D004196:Disease Outbreaks; D062665:Epidemiological Monitoring; D006801:Humans; D007303:Insect Vectors / Q000821:virology*; D007558:Italy / Q000453:epidemiology; D014887:Weather; D014901:West Nile Fever / Q000453:epidemiology*; D014902:West Nile virus / Q000302:isolation & purification*