Vaccinia virus particle (VV), coloured transmission electron micrograph (TEM). VV is composed of a DNA (deoxyribonucleic acid) core (orange), surrounded by a protein coat (yellow) and a lipid envelope (green). Vaccinia causes cowpox, a disease of cattle and humans, which produces skin lesions. This variant is a vaccine strain, used to vaccinate against smallpox, a related but more deadly human disease. Magnification: x64,000 when printed 10 centimetres wide.