Monkeypox is a viral zoonosis (a virus transmitted to humans from animals) with symptoms similar to those seen in the past in smallpox patients, although it is clinically less severe. With the eradication of smallpox in 1980 and subsequent cessation of smallpox vaccination, it has emerged as the most important orthopoxvirus. Monkeypox occurs in Central and West Africa, often in proximity to tropical rainforests.
Human monkeypox was first identified in humans in 1970 in the Democratic Republic of the Congo (then known as Zaire) in a 9-year-old boy in a region where smallpox had been eliminated in 1968. Since then, most cases have been reported from rural, rainforest regions of the Congo Basin, particularly in the Democratic Republic of the Congo, where it is considered to be endemic. Since 1970, human cases of monkeypox have been reported from 11 African countries – Benin, Cameroon, the Central African Republic, the Democratic Republic of the Congo, Gabon, Ivory Coast, Liberia, Nigeria, the Republic of the Congo, Sierra Leone, and South Sudan. In 2017 Nigeria experienced the largest documented outbreak, 40 years after the last confirmed case. The true burden of monkeypox is not known. For example, in 1996–97, a major monkeypox outbreak was suspected in the Democratic Republic of Congo with, however, a lower case fatality and a higher attack rate than usual. Some patient samples tested positive for varicella virus and some contained both varicella and monkeypox viruses. Concurrent outbreaks of chickenpox and monkeypox could explain a change in transmission dynamics in this case.
The virus has been exported from Africa a few times. In the spring of 2003, monkeypox cases were confirmed in the United States of America. Most patients were reported to have had close contact with pet prairie dogs that were infected by African rodents that had been imported into the country from Ghana. Recently, monkeypox was carried to Israel in September 2018, to the United Kingdom in September 2018 and December 2019 and to Singapore in May 2019 by travellers from Nigeria who fell ill with monkeypox after arrival. A health worker was infected and became ill.