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Further WNV info
VLA & WNV
West Nile virus (WNV)
What is West Nile virus?
West Nile Virus (WNV) is a flavivirus that is primarily transmitted and amplified between avian reservoir hosts and many species of mosquitoes and other biting insects in enzootic cycles.
The virus is antigenically related to Japanese encephalitis, Murray Valley encephalitis, St Louis encephalitis and Usutu viruses and has been associated with encephalitis in humans, horses and some species of birds. The virus has also been detected in a wide range of other animals including reptiles and amphibians.
Geographic location
WNV is endemic in parts of Africa, the Middle East and South West Asia. More recently, outbreaks of WNV have occurred in more temperate zones, including Eastern Europe, Russia, France, Italy and Portugal.
In 1999, WNV was reported for the first time in the United States resulting in outbreaks of encephalitis in the human population in and around New York.
Subsequently the disease spread to the whole of North America resulting in over 700 human fatalities and the death of many thousands of horses and wild birds.
Every year since 2001, the VLA has carried out WNV surveillance in targeted species of wild birds in the UK. However, no evidence for the presence of WNV has been obtained in any of the submissions to date.
For further information see: Phipps LP et al (2008). Surveillance for West Nile virus in British birds (2001 to 2006). Veterinary Record 162: 413-5.
Clinical signs
Horses and other equidae will show listlessness, stumbling and incoordination, weakness of limbs, ataxia, partial paralysis or death. A fever is not usually observed in equines.
In humans, the most common symptoms are a fever and headache, but can include a rash, swollen lymph nodes and conjunctivitis. In severe cases, the symptoms include the rapid onset of severe headache, high fever, stiff neck, disorientation, muscle weakness, paralysis, coma or death.