The virus is commonly found in Africa, Europe, the Middle East, North America and West Asia. The World Health Organization (WHO) documents that it was first isolated in a woman in the West Nile district of Uganda in 1937. It was identified in birds (crows and columbiformes like doves and pigeons) in the Nile delta region in 1953. Before 1997, WNV was not considered pathogenic for birds — but then, a more virulent strain caused the death in Israel of different bird species, presenting signs of encephalitis and paralysis. Human infections attributable to WNV have been reported in many countries in the World for over 50 years, the WHO says.