Smallpox is a disease similar to chicken pox, but not exactly the same. Smallpox is caused by a virus called Variola and is a member of the genus orthopoxvirus. The virus is a large brick shaped DNA virus. Smallpox spreads by direct, face to face contact with an infected person or by contact with infected body fluids or contaminated objects such as clothing. Smallpox is rarely spread through airborne transmission and is not known to be transmitted by animals or insects. The incubation period lasts from 7 to 17 days, during which infected individuals often show no symptoms and are not contagious. The lifecycle of poxviruses is complicated by having multiple infectious forms, with differing mechanisms of cell entry. Smallpox reproduces in a unique way among DNA viruses in that they replicate in the cytoplasm of the cell rather than in the nucleus. In order to replicate smallpox produce a variety of specialized proteins not produced by other DNA viruses, the most important of which is a viral-associated DNA-dependent RNA polymerase (CDC, 2004).
Allbee, Miranda and Smith, Brandon, "Smallpox Infectious Disease" (2015). Infectious Diseases Project 2015. 1.