Herpes simplex virus particle, coloured transmission electron micrograph (TEM). Each particle (virion) consists of a deoxyribonucleic acid (DNA) genome surrounded by an icosahedral capsid (orange), which is itself surrounded by an envelope (blue). When the envelope breaks and collapses away from the capsid, negatively stained virions have the typical insfried-eggins appearance that is seen here. Herpes simplex is one of the most common viral pathogens in humans. It causes inflammation of the skin and mucous membranes, characterized by fluid-filled blisters. Magnification: x156,000 when printed 10 centimetres wide.