West Nile Virus
It´s a disease caused by an arthropod born flavivirus, carried by mosquitoes, who cause encephalitis that affect humans and animals, such as horses, sometimes with fatal results.
It´s important to understand that both horses and people are end stage hosts and are not infectious to other horses or people. Many infected animals show no signs of illness although they produce detectable blood antibody levels.
In areas where the virus occurs, wild birds which are commonly infected by mosquitoes, act as a source of replicating the virus. Clinical signs in horses range from a loss of appetite and depression to fever, weakness or paralysis of the hind limbs, ataxia, blindness or excessive excitability, coma, collapse and death.
When a horse is suspected of having WNV blood tests should be performed. There isn´t a specific treatment for West Nile virus. Horses that need to compete internationally, vaccination appears to be a sensible precaution.
This article is based in scientific veterinary literature.