Illustration of smallpox virus particles. The virus particles are covered in a viral membrane (transparent) derived from its host cell. Inside this lies the core, which contains the particle's DNA (deoxyribonucleic acid) genetic material. The core has a biconcave shape. The surface of the virus is covered with surface tubules which help the virus in attachment to a host cell. 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.