West Nile Virus is part of a family of viruses known as Flaviviruses, along with other known viruses such as Hepatits C, St Louis Virus and Yellow fever.
West Nile virus is transmitted by several species of mosquitoes. Most humans infected will only have minor, if any, symptoms.
More serious cases can cause symptoms of headaches, fever, muscle pains (this is not a full list of the symptoms).
Very rarely does is have extremely serious complications such as meningitis (inflammation of the brain coverings) or encephalitis (inflammation of the brain itself).
Serious infection is more common in immunocompromised people, like people with HIV or people on some sort of immunosuppressive therapy for a chronic disease, like cancer or Crohn’s disease. People with high blood pressure or type 2 diabetes are also at higher risk.
There is no vaccine against this infection. The best way to protect yourself is to wear insect repellant on days spent outdoors.