West Nile Virus Infection

West Nile virus (WNV) is an arthropod-borne virus transmitted mainly by mosquito bites. Wild avifauna constitutes its natural reservoir. Mammals are dead-end hosts as they generally do not develop a viraemia high enough to trigger a new infection cycle. WNV belongs to the Flavivirus genus and can be responsible for a disease known as WN fever. Humans and horses are the most sensitive hosts as they may develop severe neurological signs. WNV has a worldwide distribution and caused numerous outbreaks since the late 1990s, most notably in North America and Europe. Lineage 1 strains have caused the most severe outbreaks to date. However, the situation has recently evolved with the emergence in the late 2000s of pathogenic lineage 2 strains in South Africa, Russia and Eastern and Southern Europe. Many developments in the fields of WN diagnosis and vaccination have been described in the recent years and may help control WNV spread. Key Concepts West Nile virus (WNV) is a zoonotic arbovirus mainly transmitted by mosquitoes. It is an enveloped, positive-stranded RNA virus belonging to the genus Flavivirus in the family Flaviviridae. WNV has a wide geographical range that includes Europe, the Middle East, Western Asia, Africa, Australia (Kunjin virus) and North, Central and South America. Most WNV infections are asymptomatic, but can be responsible for a disease known as WN fever (10–20% of WNV infections) or severe neurological signs (1–10% of WNV infections) in humans and horses. Humans and horses are the most sensitive hosts. Since the late 1990s, pathogenic WNV strains have begun to emerge. Diagnosis can be difficult as flaviviruses are antigenically related. There are no effective drugs or treatments against WNV infections. Approved vaccines are available in equids, and human vaccines are under development. Control of WNV outbreaks largely depends on vector control measures and interventions. Keywords: West Nile; Flavivirus; arthropod-borne virus infection; RNA virus; neuroinvasive; emergence; human; horse; bird