Illustration showing the structure of a smallpox virus particle. The core (red, centre) contains the particle's DNA genetic material. The core has a concave shape and is overlaid with several layers of a membrane derived from its host cell. The depressions in its upper and lower surface contain lateral bodies (pink), the function of which is unknown. Smallpox is a disease that causes fever and often death. It was eradicated after a worldwide effort in the 1970s, but strains exist in research laboratories.