False-colour transmission electron micrograph (TEM) of virions (virus particles) of the rotavirus. Individual virions consist of a protein capsid surrounding a core of double-stranded RNA. Rotaviruses belong to the Reovirus class, whose members possess icosahedral symmetry, are 65-75 nanometers in size and are non-enveloped. Other members of virus families are surrounded by a lipoprotein envelope that is often derived from the host cell's membranes. The rotavirus causes infective diarrhoea, especially in children and the elderly. Magnification: X 100,000 at 35mm size.