Monkeypox is a zoonotic viral disease that can infect nonhuman primates, rodents and some other mammals. Monkeypox results from infection by the monkeypox virus, a member of the genus Orthopoxvirus in the family Poxviridae. Two clades of monkeypox viruses, the West African and Congo Basin viruses have been identified. The Congo Basin viruses are more virulent.
The symptoms of monkeypox are similar to but milder than the symptoms of smallpox. Monkeypox begins with fever, headache, muscle aches, and exhaustion. The main difference between symptoms of smallpox and monkeypox is that monkeypox causes lymph nodes to swell (lymphadenopathy) while smallpox does not. The incubation period for monkeypox is usually 7−14 days but can range from 5−21 days. Monkeypox can be tentatively diagnosed if the characteristic skin lesions are present and there is a history of exposure.
Human monkeypox from 1981 to 1986 in the DRC identified 338 cases. The case-fatality rate was 9.8% for persons not vaccinated with vaccinia vaccine, which was about 85% efficacious in preventing human monkeypox. The secondary attack rate in unvaccinated household members was 9.3%, and 28% of case-patients reported an exposure to another case-patient during the incubation period.