Classification
Smallpox has two clinical forms: Variola major and Variola minor. Variola major is more common and also more severe. Variola minor is less common and less severe. The classification of viruses is called the ICTV system and it is similar to the classification of cellular organisms. Viruses are classified by order, then family, then subfamily, then genus, then species. An order is a group of families that share certain characters. The name of the order consists of a single word ending in virales. A family is a group of genera sharing certain characters regardless of whether they are they are organized into subfamilies. A family name consists of a single word ending in viridae. A subfamily is a group of genera sharing certain characters and is only used when needed to solve complex hierarchical problems. A subfamily name is a single word ending in virinae. A genus is a group of species that share significant properties and often only differ in host range and virulence. A genus name must be a single word ending in virus. A species is one specific virus and its name must provide an unambiguous identification of the species. The classification of smallpox is: Order: Unassigned, Family: Poxviridae, Subfamily: Chordopoxvirinae, Genus: Orthopoxvirus, Species: Variola.