Viruses. Composite image of coloured transmission electron micrographs (TEM) of four types of viruses. The collage contains papilloma viruses (orange, upper left), an adenovirus (orange, upper right), two rotaviruses (yellow, lower left) and a herpes virus (green, lower centre). The envelope of the herpes virus is seen. Adenoviruses infect the respiratory tract, the eyes and the gut. Papilloma viruses cause warts, rotaviruses can cause diarrhoea, and herpes viruses cause cold sores. All these viruses display regular cubic symmetry. The relative sizes are approximately to scale. Magnification unknown.