Eighty per cent (80%) of infected with West Nile virus people remain asymptomatic, 20% come up with mild symptoms, while less than 1% appear with severe manifestations from the central nervous system.
-Asymptomatic: 80% of people infected with the virus, ie 4 out of 5, do not have any symptom; thus, they may have already been infected and probably do not know it.
-Mild disease: 20% of those infected with the virus come up with mild clinical manifestations such as fever, muscle and joint pain, rash (occasionally) and lymph node enlargement. From the time of the infection till the time of symptoms experience, there is an interval of 2-14 days - a period that may be prolonged in people with immunocompression. Symptoms usually last 5-7 days and then draw back.
-Severe disease: less than 1% of people infected with the virus will develop serious clinical picture with symptoms from the central nervous system (meningitis/emcephalitis). Symptoms of this form of the disease include high fever and severe headache, disorientation and behaviour changes, convulsions, paralysis, coma.
Immunosuppressed and people over 65 years old are the most vulnerable for severe disease of WNV and death.