Orthopoxvirus is a genus of viruses in the family Poxviridae and subfamily Chordopoxvirinae. Vertebrates, including mammals and humans, and arthropods serve as natural hosts. There are currently ten species in this genus including the type species vaccinia virus. Diseases associated with this genus include smallpox, cowpox, horsepox, and monkeypox. The most famous member of the genus is variola virus, which causes smallpox. Variola was eradicated using vaccinia virus as a vaccine.