Evidence of mosquito-transmitted flavivirus circulation in Piedmont, north-western Italy

Abstract

BackgroundFlavivirus is a highly heterogeneous viral genus that includes important human pathogens and several viral strains with unknown zoonotic potential. Mosquito-borne flaviviruses have been isolated and characterized in Northern Italy: West Nile virus and Usutu virus were detected in mosquitoes and in different host species and recent studies provided evidence about the circulation of “insect Flavivirus” strains.MethodsIn order to clarify the diffusion and the distribution of the mosquito-transmitted flaviviruses in Italy, we analyzed Culex and Ochlerotatus mosquitoes collected in 2009 and 2010 in an area divided evenly between hills and plains and where the landscape is dominated by mixed agricultural patches, rice fields, deciduous tree forests, and urban environments. Each mosquito pool was tested for the presence of Flavivirus strains and we characterized positive samples by genetic sequencing.ResultsPositive mosquito pools revealed low infection prevalence, but suggested a continuous circulation of both Usutu virus and insect Flavivirus. Interestingly, phylogenetic analyses based on NS5 gene partial sequences showed a closer relationship among new Usutu virus strains from Piedmont and the reference sequences from the Eastern Europe, with respect to Italian samples characterized so far. Moreover, NS5 gene phylogeny suggested that mosquito flaviviruses found in Italy could belong to different lineages.ConclusionsOur results contribute to a wider point of view on the heterogeneity of viruses infecting mosquitoes suggesting a taxonomical revision of the Mosquito-borne Flavivirus group.

Wide detection of Aedes flavivirus in north-eastern Italy – a European hotspot of emerging mosquito-borne diseases

“…The prevalence of AeFV infection in Aedes albopictus in both regions was higher than the prevalence of other ISFs in other mosquito species collected within the two regions and this is in agreement with similar studies that were carried out either in Italy (Calzolari et al, 2010a(Calzolari et al, , 2012bCerutti et al, 2012) or abroad (Tyler et al, 2011;Machado et al, 2012; Zuo et al, 2014). In previous studies, seasonality was shown to be an important factor affecting AeFV detection (Kim et al, 2009;Calzolari et al, 2010a).…”

“…Moreover, the prevalence of AeFV in Aedes albopictus in Trentino was higher than in Veneto and this result is supported by previous research carried out in 2008(Roiz et al, 2009, and it was also higher compared with the prevalence of ISFs detected in other northern Italian regions (e.g. Lombardia, Emilia-Romagna and Piemonte) (Roiz et al, 2009(Roiz et al, , 2012Calzolari et al, 2010a Calzolari et al, , b, 2012aCalzolari et al, , 2013aCerutti et al, 2012;Ravanini et al, 2012;Pautasso et al, 2013).These results support the hypothesis that the local ecological and climatic conditions may shape not only the abundance and distribution of mosquito populations (Roiz et al, 2010(Roiz et al, , 2011Trawinski & Mackay, 2010), but also their viral infection pattern (Newman et al, 2011;Calzolari et al, 2012b;Obara-Nagoya et al, 2013). The ecological and climatic conditions of the two study areas differ not only in climate, but also in the degree of anthropization, biodiveristy and land use.…”

“…Lelli et al, 2008;Manarolla et al, 2010;Tamba et al, 2011; Vázquez et al, 2011;Cerutti et al, 2012;Ravanini et al, 2012;Buchebner et al, 2013;Calzolari et al, 2013a; Höfle et al, 2013). In Europe, USUV has been recognized as a candidate human pathogen in Austria (Weissenböck et al, 2007), Italy (Cavrini et al, 2009;Pecorari et al, 2009;Savini et al, 2011;Gaibani et al, 2012Gaibani et al, , 2013Pierro et al, 2013) and Croatia (Vilibic-Cavlek et al, 2014), but the pathogenicity for humans still requires further assessment.…”

“…Since then, it has been detected in wild-caught mosquitoes in Puerto Rico (Cook et al, 2006), Thailand (Kihara et al, 2007 and Mexico (Espinoza-Gó mez et al, 2011). Over the past 40 years, many other ISFs have been isolated and identified from field-collected mosquitoes, belonging to different species, in several locations (Ferreira et al, 2013;Haddow et al, 2013; Papa et al, 2014 Calzolari et al, 2010a Calzolari et al, , b, 2012aCalzolari et al, , 2013aCerutti et al, 2012;Ravanini et al, 2012;Pautasso et al, 2013). Moreover, DNA sequences related to AeFV were identified in wild Aedes albopictus mosquito collected in 2007(Roiz et al, 2009).…”

Usutu virus: current knowledge and future perspectives

“…51 During a regional WNV surveillance program based on reverse transcription polymerase chain reaction (RT-PCR) detection conducted in Italy in the same year, 56 pools (54 of C. pipiens and 2 of Aedes albopictus) out of 1,789 mosquito pools were USUV positive by RT-PCR, 52 and similar results have been reported since then in different regions of Italy. [53][54][55][56][57] These findings confirm the role of Culex species as the main vector in the virus cycle, although Aedes mosquitoes also play a role on it, and point to an association between the presence of USUV-positive mosquitoes and drought conditions and a wide temperature range. USUV was also isolated from a pool of C. pipiens mosquitoes trapped in summer of 2010 in Germany 58 and from Culex modestus in Czech Republic the same year.…”