Monkeypox is caused by an Orthopoxvirus named monkeypox. The viruses are oval brick-shaped viruses that have a lipoprotein layer with tubules or filaments that cover the viral DNA. There are many members of this viral genus, including such species as variola (smallpox), cowpox, buffalopox, camelpox, rabbitpox, and others. Most species infect a particular animal species but occasionally may infect other mammals.
Figure 1: Monkeypox virus, brick-shaped negative stained virus grown in tissue cultures, visualized by electron microscopy; SOURCE: CDC/Cynthia S. Goldsmith, Inger K. Damon, and Sherif R. Zaki
Transmission of monkeypox is usually by direct contact with infected animals or possibly by eating poorly cooked meat from an infected rodent or monkey. Cutaneous or mucosal lesions on the infected animals are a likely source of transmission to humans, especially when the human skin is broken due to bites, scratches, or other trauma — are a likely source for virus infection. Person-to-person transfer, probably by infected respiratory droplets, is possible but is not often documented. One study suggested that only about 8%-15% of infections were transmitted person to person among close family members.