Monkeypox was first identified as a distinct illness in 1958 among laboratory monkeys in Copenhagen, Denmark. The first documented cases in humans was in 1970, in six unvaccinated children during the smallpox eradication efforts; the first being a 9-month old boy in the Democratic Republic of the Congo (formerly Zaire). The others, including three who were playmates, were in Liberia and Sierra Leone. It was noted to be less easily transmissible than smallpox. From 1981 to 1986, over 300 cases of human monkeypox were reported in the DRC, the majority being due to contact with animals. In 1996, the disease reemerged in the DRC with 88% of cases resulting from human-to-human transmission. 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. In humans, the disease remained confined to the rain forests of Western and Central Africa until 2003, when an outbreak of monkeypox occurred in the US. All cases were traced to sick rodents imported from Ghana. Local prairie dogs caught the infection and passed it onto their owners. The disease was found to be mild and there were no deaths. Between 1970 and 2019 the disease was reported in 10 African countries; mostly in Central and West Africa.
In 1970, monkeypox was first associated with an illness as a disease in humans in the Democratic Republic of the Congo (formerly Zaire), in the town of Basankusu, Équateur Province. Although it was once thought to be uncommon in humans, cases increased since the 1980s, possibly as a result of waning immunity since the stopping of routine smallpox vaccination.
Several species of mammals are suspected to act as a natural reservoir of the virus. Although it was once thought to be uncommon in humans, the quantity and severity of outbreaks has significantly increased since the 1980s, possibly as a result of waning immunity since the stopping of routine smallpox vaccination. The first cases in humans were found in 1970 in the Democratic Republic of the Congo (DRC). There have been sporadic cases in Central and West Africa, and it is endemic in the DRC. The 2022 monkeypox outbreak represents the first incidence of widespread community transmission outside of Africa, which was initially identified in the United Kingdom in May 2022, with subsequent cases confirmed in at least 74 countries in all continents except Antarctica. On 23 July 2022, the World Health Organization (WHO) declared the outbreak a Public Health Emergency of International Concern (PHEIC) with more than 53,000 reported cases in 75 countries and territories.
There is no known cure. A study in 1988 found that the smallpox vaccine was around 85% protective in preventing infection in close contacts and in lessening the severity of the disease. A newer smallpox and monkeypox vaccine based on modified vaccinia Ankara has been approved, but with limited availability. Other measures include regular hand washing and avoiding sick people and animals. Antiviral drugs, cidofovir and tecovirimat, vaccinia immune globulin and the smallpox vaccine may be used during outbreaks. The illness is usually mild and most of those infected will recover within a few weeks without treatment. Estimates of the risk of death vary from 1% to 10%, although few deaths as a consequence of monkeypox have been recorded since 2017.
Between 1981 and 1986 WHO surveillance in DRC/Zaire recorded 338 confirmed cases and 33 deaths (CFR 9.8%). In 1996–1997, a second outbreak of human illness was identified in DRC/Zaire and between 1991 and 1999, 511 cases were reported in DRC/Zaire. Clade I of disease remains endemic in DRC and has a higher CFR than the other genetic clade in Western Africa.
By May 2022, the case fatality rate (CFR) of past outbreaks was around 3%–6%, while the CFR of the 2022 outbreak remains below 1%. No human-to-human transmission was documented until the 2022 monkeypox outbreak in Europe. Clade II had an outbreak – the first outbreak of monkeypox outside of Africa – in Midwestern United States among owners of pet prairie dogs in 2003. Seventy-one people were reportedly infected, of whom none died.
In May 2003, a young child became ill with fever and rash after being bitten by a prairie dog purchased at a local swap meet near Milwaukee, Wisconsin. In total, 71 cases of monkeypox were reported through June 20, 2003. All cases were traced to Gambian pouched rats imported from Accra, Ghana, in April 2003 by a Texas exotic animal distributor. No deaths resulted. Electron microscopy and serologic studies were used to confirm that the disease was human monkeypox.
As of 2018, monkeypox was traditionally restricted to the ecology of tropical rainforests. although the pattern was broken in 2005, when 49 cases were reported in Sudan (areas now South Sudan), with no fatalities. The genetic analysis suggested that the virus did not originate in Sudan but was imported, most likely from DRC.
In September 2017, human monkeypox re-emerged in Nigeria, 39 years since it had been last reported. The subsequent 2017–18 Nigerian human monkeypox outbreak was, at that time, the largest ever outbreak of clade II of the virus, with 118 confirmed cases. Unlike previous outbreaks of this clade, infection was predominantly among young male adults and human-to-human transmission appears to have readily occurred. Seven deaths (5 male, 2 female, case fatality rate of 6%) were reported, including a baby and four HIV/AIDS patients. Additionally, a pregnant woman in her second trimester had a spontaneous miscarriage due to monkeypox infection.
The Niger Delta University Teaching Hospital reported that a substantial number of its young adult cases had concomitant genital ulcers, syphilis and HIV infection. Monkeypox spread around southeast and south Nigeria with some states and the federal government of Nigeria seeking ways to contain it. By December 2017 it spread to Akwa Ibom, Abia, Bayelsa, Benue, Cross River, Delta, Edo, Ekiti, Enugu, Imo, Lagos, Nasarawa, Oyo, Plateau, Rivers and Federal Capital Territory. The outbreak started in September 2017 and remained ongoing across multiple states as of May 2019.
In 2018, cases of monkeypox were diagnosed in the UK in two unrelated travellers from Nigeria. That year the first human-to-human transmission outside of Africa was confirmed in the UK. This person was a healthcare worker who possibly contracted the disease from contaminated bedlinen. Cases were also reported in travellers to Israel and Singapore. The UK saw further cases in 2019 and 2021.
In September 2018, the United Kingdom's first case of monkeypox was recorded. The person, a Nigerian national, is believed to have contracted monkeypox in Nigeria before travelling to the United Kingdom. According to Public Health England, the person was staying in a naval base in Cornwall before being moved to the Royal Free Hospital's specialised infectious disease unit. People who had been in contact with the person since he contracted the disease were contacted.
On 8 May 2019, a 38-year-old man who travelled from Nigeria was hospitalised in an isolation ward at the National Centre for Infectious Diseases in Singapore, after being confirmed as the country's first case of monkeypox. As a result, 22 people were quarantined. The case may have been linked to a simultaneous outbreak in Nigeria.
A second case was confirmed in the town of Blackpool, with a further case that of a medical worker who cared for the case from Blackpool. A fourth case occurred on 3 December 2019, when monkeypox was diagnosed in a person in south west England. They were travelling to the UK from Nigeria.
In May 2022, the Nigerian government released a report stating that between 2017 and 2022, 558 cases were confirmed across 32 states and the Federal Capital Territory. The Rivers State was the most affected by monkeypox followed by Bayelsa and Lagos. There were 8 deaths reported, making for a 3.5% Case Fatality Ratio. In 2022, NCDC implemented a National Technical Working Group for reporting and monitoring infections, strengthening response capacity.
In June 2022, the World Health Organization announced that it would find a new name for the disease, in line with its policy to avoid misleading associations with specific regions or animals.
According to a CDC report, 41% of cases of monkeypox were among HIV-positive patients (136 out of 334 patients) between May and July 2022. The New England Journal of Medicine (NEJM) also looked at more than 500 cases from different countries and found that 41% of them were among HIV patients. In addition, a study published in The Lancet that looked at nearly 200 cases in Barcelona and Madrid discovered that 40% were HIV-positive. Patel and colleagues observed 197 patients from sexual health centres in south London between May and July 2022. They reported 35.5% patients had HIV-1 co-infection. 91.4% of these participants were receiving antiretroviral therapy and 78.6% had an undetectable HIV-1 viral load (<200 copies). The median CD4 count was 664 cells (interquartile range 522-894 cells). The proportion of HIV-positive individuals in these reports is significantly higher than the HIV rate among men who have sex with other men. The reasons for this heavy overrepresentation of men living with HIV among monkeypox cases are not fully understood yet.
On 31 July 2022, the first death from monkeypox was recorded in India: a 22-year-old man who had returned from the UAE died.