Monkeypox is caused by the monkeypox virus Orthopoxvirus simiae (MPXV) of the genus Orthopoxvirus. The virus is related to the classical human poxvirus (variola, smallpox) and the cowpox virus, which is also known to be a zoonotic pathogen. The name is misleading, as monkeypox were first detected in monkeys at the end of the 1950s, their real animal reservoir however probably are rodents.
Monkeypox naturally occurs in West and Central Africa, it was detected in various rodent species (squirrels, rats, dormice) and shrews.
In addition to a series of animal species, humans are also susceptible to infection, i.e. monkeypox is a zoonosis. Monkeys, like humans, are dead-end hosts of the monkeypox virus.
Until May 2022, human infections occurred mostly as travel illnesses in persons who had visited African countries where the pathogen occurs naturally. The cases that have occurred as of May 2022 are the first cases resulting from a more widespread human-to-human transmission outside of Africa.