Orthopoxviruses (pox), also known as poxviruses, are a family of viruses belonging to the group of nucleocytoplasmic large DNA viruses (NCLDV). At 400-500nm, poxviridae are the largest viruses we know of. The orthopoxvirus family is divided into the subfamilies Entomopoxvirinae and Chordopoxvirinae. Human pathogenic species are only found in the subfamily Chordopoxvirinae. For further information see below. Poxviridae.