Monkeypox virus (MPV or MPXV) is a double-stranded DNA virus that causes monkeypox in humans and other animals. It belongs to the genus Orthopoxvirus in the family Poxviridae. It is one of the human orthopoxviruses that includes variola (VARV), cowpox (CPX), and vaccinia (VACV) viruses. It is not a direct ancestor to, nor a direct descendant of, the variola virus, which causes smallpox. Monkeypox disease is similar to smallpox, but with a milder rash and lower mortality rate.
Variation in virulence of the virus has been observed in isolates from Central Africa, where strains are more virulent than those from Western Africa. The two areas have distinct clades of the virus, termed Congo Basin (Central African) and West African clades.
Monkeypox is carried by animals including primates. It was first identified by Preben von Magnus in Copenhagen, Denmark, in 1958 in crab-eating macaque monkeys (Macaca fascicularis) being used as laboratory animals. The 2003 outbreak in the United States was traced to prairie dogs infected from an imported Gambian pouched rat.
The virus can spread both from animal to human and from human to human. Infection from animal to human can occur via an animal bite or by direct contact with an infected animal’s bodily fluids. The virus can spread from human to human by both droplet respiration and contact with fomites (touchable surfaces) from an infected person’s bodily fluids. The incubation period is between 10 and 14 days. Prodromal symptoms include swelling of lymph nodes, muscle pain, headache, fever, prior to the emergence of the rash.
The virus is mainly found in the tropical forests of Central Africa and West Africa. It was first discovered in monkeys in 1958, and in humans in 1970. Between 1970 and 1986, over 400 cases in humans were reported. Small viral outbreaks with a death rate in the range of 10% and a secondary human-to-human infection rate of about the same amount occur routinely in equatorial Central and West Africa.
The primary route of infection is thought to be contact with the infected animals or their bodily fluids.
Outbreak of infection in 2022
The first cases of widespread community transmission of monkeypox outside Africa occurred in an outbreak that started in the UK in May 2022 and is still ongoing. The outbreak is with the mild West African variant. The outbreak has spread to a number of countries, first reported from the United States, Spain, Portugal and Sweden, later also Austria, Germany, Belgium, France, Italy, Portugal Norway, Canada and Australia. On May 20, 120 confirmed or suspected cases of outside Africa were reported. On 23 May 2022, the Danish Patient Safety Authority announced that the first Danish case of the outbreak had been diagnosed. The patient had been travelling in Spain.