title: Phylogenetic relationships of Western Mediterranean West Nile virus strains (1996-2010) using full-length genome sequences: single or multiple introductions?
abstract: In recent years, West Nile virus (WNV) has re-emerged in the Western Mediterranean region. As a result, the number of complete WNV genome sequences available from this region has increased, allowing more detailed phylogenetic analyses, which may help to understand the evolutionary history of WNV circulating in the Western Mediterranean. To this aim, the present work describes six new complete WNV sequences from recent outbreaks and surveillance in Italy in 2008-2009 and in Spain in 2008 and 2010. Comparison with other sequences from different WNV clusters within lineage 1 (clade 1a) confirmed that all Western Mediterranean WNV isolates obtained since 1996 (except one from Tunisia, collected in 1997) cluster in a single monophyletic group (here called 'WMed' subtype). The analysis differentiated two subgroups within this subtype, which appear to have evolved from earlier WMed strains, suggesting a single introduction in the area, and further dissemination and evolution. Close similarities between WNV variants circulating in consecutive years, one in Spain, between 2007 and 2008, and another in Italy between 2008 and 2009, suggest that the virus possibly overwinters in Western Mediterranean sites. The NS3(249)-proline genotype, recently proposed as a virulence determinant for WNV, has arisen independently at least twice in the area. Overall, these results indicate that the frequent recurrence of outbreaks caused by phylogenetically homogeneous WNV in the Western Mediterranean since 1996 is consistent with a single introduction followed by viral persistence in endemic foci in the area, rather than resulting from independent introductions from exogenous endemic foci.
authors.affiliation: Centro de Investigación en Sanidad Animal (CISA)-INIA, Ctra. Algete-El Casar s/n, 28130 Valdeolmos, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Sotelo
authors.affiliation: Centro de Investigación en Sanidad Animal (CISA)-INIA, Ctra. Algete-El Casar s/n, 28130 Valdeolmos, Spain.
authors.forename: Jovita
authors.initials: J
authors.lastname: Fernández-Pinero
authors.affiliation: Centro de Investigación en Sanidad Animal (CISA)-INIA, Ctra. Algete-El Casar s/n, 28130 Valdeolmos, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Llorente
authors.affiliation: National Center for Microbiology, Instituto de Salud Carlos III, Majadahonda, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Vázquez
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna (IZSLER), Brescia, Italy.
authors.forename: Ana
authors.initials: A
authors.lastname: Moreno
authors.affiliation: Laboratorio Central de Veterinaria, Ctra Algete km. 8, 28110 Algete, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Agüero
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna (IZSLER), Brescia, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Cordioli
authors.affiliation: National Center for Microbiology, Instituto de Salud Carlos III, Majadahonda, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Tenorio
authors.affiliation: Centro de Investigación en Sanidad Animal (CISA)-INIA, Ctra. Algete-El Casar s/n, 28130 Valdeolmos, Spain.
authors.forename: Miguel Ángel
authors.initials: MÁ
authors.lastname: Jiménez-Clavero
mesh_terms: D000818:Animals; D001715:Bird Diseases / Q000453:epidemiology* / Q000821:virology; D016000:Cluster Analysis; D004196:Disease Outbreaks; D016679:Genome, Viral; D007558:Italy / Q000453:epidemiology; D008969:Molecular Sequence Data; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics*; D017422:Sequence Analysis, DNA; D013030:Spain / Q000453:epidemiology; D014901:West Nile Fever / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D014902:West Nile virus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D012367:RNA, Viral