West Nile virus

Other Scientific Names

• West Nile-like virus

International Common Names

• English: WN virus

English acronym

• WNLV
• WNV

• Domain: Virus
•     Group: "Positive sense ssRNA viruses"
•         Group: "RNA viruses"
•             Order: Nidovirales
•                 Family: Flaviviridae
•                     Genus: Flavivirus
•                         Species: West Nile virus

WNV virions are approximately 40 nm in diameter, spherical and contain a lipid envelope. The positive-sense single stranded RNA genome is 11.3 kb in size and contains three structural and seven non-structural proteins. The structural proteins comprise a capsid protein (C), the major envelope protein (E) and either a prM (immature virion) or M (mature virion). WNV is stable at an alkaline pH of 8.0 but is readily inactivated by acidic pH, temperatures above 40°C, organic solvents, detergents, UV-light and gamma-irradiation.

Two genetic lineages have been described (Berthet et al., 1997). Lineage 1 includes isolates from Europe, the Middle East, Africa, India, Australia (KUNV) and from North America (Lanciotti et al., 1999). Lineage 2 includes isolates from West, Central and East Africa and Madagascar which have not been associated with disease outbreaks. Scherret et al. (2001) suggested on the basis of genetic and antigenic analyses that WN viruses should be subdivided into at least 6 subtypes.

The close antigenic relationship of WNV to other flaviviruses is demonstrated in binding assays such as ELISA and haemagglutination-inhibition (HI) using polyclonal and monoclonal antibodies. Neutralising assays are more discriminating, with the envelope glycoprotein E the main target for neutralising antibody. The E protein is also responsible for inducing protective immunity.