Monkeypox virus: Know what it is, how it spreads, what causes it | The ... Monkeypox is a viral disease caused by the monkeypox virus which is a member of the Orthopoxvirus genus in the family Poxviridae; this virus is associated with diseases like smallpox, cowpox, horsepox, and camelpox. The symptoms of monkeypox are similar to that of smallpox, which was declared eradicated in the 1980s.