About Monkeypox

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.

Cases of Monkeypox Since 1970
Country Year Recorded Human Cases*
Cameroon 1979 2
Cameroon 1989 4
Cameroon 2018 1
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
Gabon 1987 5
Israel 2018 1 §
Liberia 1970 4
Liberia 2017 2
Nigeria 1971 2
Nigeria 1978 1
Nigeria 2017-present 446
Republic of Congo 2003 11
Republic of Congo 2009 2
Republic of Congo 2017 88
Sierra Leone 1970 1
Sierra Leone 2014 1
Sierra Leone 2017 1
Singapore 2019 1
Sudan 2005 19**
United Kingdom 2018 3††
United Kingdom 2021 3
United States 2003 47§§
United States 2021 1***

* 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.

Image of a child affected with monkeypox.

Child affected with monkeypox.