Orthopoxviruses come from the poxiviridae family of viruses. They are responsible for several diseases, most notably smallpox and (now) monkeypox. They are brick-shaped, enveloped, and highly complex viruses about 250nM wide and around 300nM wide. This virus contains a very long (170-150kb) linear double-stranded DNA genome.
Cell entry is mediated by the membrane proteins that induce endocytosis of the virus in the cell cytoplasm. From here, the viral core is released and early phase expression begins quickly. Eventually the viral genome is exposed and intermediate gene expression and DNA replication begins. Late stage expression results in the viral structural proteins and assembly of new viral particles.
Variola virus is the most widely-known orthopoxvirus as it is the cause for smallpox disease. Smallpox has fortunately been eradicated for several decades. Monkeypox has also been known to pop up in outbreaks with the most recent one occurring now – the monkeypox virus is responsible for this disease.
Importantly, the vaccines that lead to the eradication of smallpox are based on the orthopoxvirus known as vaccinia virus. Vaccinia virus is still pathogenic to humans but typically more mild. It is for this reason that the live and attenuated smallpox vaccines were based on vaccinia as opposed to variola.