any of a group of viruses constituting the family Poxviridae, responsible for a wide range of pox diseases in human beings and other animals. Poxvirus was the cause in human beings of smallpox (q.v.), which was declared eradicated worldwide in 1977. (Chicken pox of human beings is caused by a herpesvirus; see herpes zoster.) The virus particle is somewhat brick-shaped, with the longest dimension as much as 250 nanometres (nm; 1 nm = 10^{- 9} metre). It is surface-studded with hollow spikes; and contains deoxyribonucleic acid (DNA). Unlike other DNA-viruses, poxviruses appear to develop entirely within the cytoplasm of affected cells. The virus of rabbit pox, or infectious myxomatosis (see myxomatosis), has been used with mixed success in Australia to control the wild-rabbit population.