West Nile virus particles. Coloured transmission electron micrograph (TEM) of West Nile virus (WNV) particles (red/orange dots) with host cells. This virus causes encephalitis (inflammation of the brain) in humans. The WNV belongs to the group of flaviviruses, which are RNA viruses that have a core (red) surrounded by an outer protein coat (orange) with a cubic symmetry. WNV is transmitted by mosquitoes and infects both humans and animals. Symptoms can range from a mild fever to spontaneous bleeding of the skin and circulatory failure, which are often fatal. WNV occurs in Africa, Asia and Europe. Magnification: x38,400 at 10 centimetres wide.