Monkeypox is a rare disease that is caused by infection with monkeypox virus. Monkeypox virus belongs to the Orthopoxvirus genus in the family Poxviridae. The Orthopoxvirus genus also includes variola virus (the cause of smallpox), vaccinia virus (used in the smallpox vaccine), and cowpox virus.
Monkeypox was first discovered in 1958 when two outbreaks of a pox-like disease occurred in colonies of monkeys kept for research, hence the name ‘monkeypox.’ The first human case of monkeypox was recorded in 1970 in the Democratic Republic of Congo during a period of intensified effort to eliminate smallpox. Since then, monkeypox has been reported in humans in other central and western African countries. Human monkeypox infections have only been documented six times outside of Africa; in the United States in 2003 (47 cases), in both the United Kingdom (3 cases) and Israel (1 case) in 2018, in Singapore in 2019 (1 case) and in both the United Kingdom (3 cases) and the United States (1 case) in 2021.
The natural reservoir of monkeypox remains unknown. However, African rodent species are suspected to play a role in transmission.
There are two distinct genetic groups (clades) of monkeypox virus—Central African and West African. Human infections with the Central African monkeypox virus clade are typically more severe compared to those with the West African virus clade and have a higher mortality. Person-to-person spread is well-documented for Central African monkeypox virus and limited with West African monkeypox.
|Country||Year||Recorded Human Cases*|
|Central African Republic||1984||6|
|Central African Republic||2001||4|
|Central African Republic||2010||2|
|Central African Republic||2015||12|
|Central African Republic||2016||11|
|Central African Republic||2017||8|
|Central African Republic||2018||14|
|Côte d’Ivoire (Ivory Coast)||1971||1|
|Côte d’Ivoire (Ivory Coast)||1981||1|
|Democratic Republic of Congo||1970-present||>1000/year †|
|Republic of Congo||2003||11|
|Republic of Congo||2009||2|
|Republic of Congo||2017||88|
* Includes laboratory-confirmed cases and suspected cases that had an epidemiologic (close contact), spatial, or temporal link to a laboratory-confirmed case
† DRC has reported >1,000 suspected cases each year since 2005
§Introduction attributed to an imported case in a traveler who visited Nigeria.
¶ Current as of July 2021. See Nigerian Centre for Disease Control for the most up to date information
** Introduction attributed to movement of the virus from Democratic Republic of the Congo. Cases occurred in an area that is now part of South Sudan
†† Introduction attributed to two unrelated imported cases among travelers who visited Nigeria.
§§ Introduction attributed to a shipment of animals imported from Ghana.
*** Patient tested positive for monkeypox after returning to the U.S. from Nigeria.
Child affected with monkeypox.