any of a group of viruses constituting the family Papovaviridae, which is divided into two subgroups: the papillomaviruses (papillomavirus) and the polyomaviruses (polyomavirus). Papovaviruses are responsible for a variety of abnormal growths in animals: warts (papillomas) in humans, dogs, and other animals; cervical cancer in women; tumours (polyomas) in mice; and vacuoles (open areas) in cells of monkeys. The virus particle lacks an outer membrane; is spheroidal, about 45 nanometres (nm; 1 nm = 10^{- 9} metre) across; is covered with 42 subunits called capsomeres; and contains deoxyribonucleic acid (DNA). Papovaviruses develop in the nuclei of cells, in which they can be seen in apparent crystalline arrangements.