orthopoxvirus
noun(or-tho-pox-vi-rus)
a genus of poxviruses that are brick-shaped measuring about 200 by 200 by 250 nanometers, that hybridize extensively within the genus and sometimes with the DNA of members of other poxvirus genera, and that include the vaccina virus and the causative agents of cowpox, monkeypox, mousepox, and smallpox