Epidemiology

The epidemiology of human monkeypox differs significantly from that of smallpox. Since 1970, when the first case of human monkeypox was reported, until early 2003, human monkeypox was endemic only to central and western Africa. MPV recently emerged in the USA. MPV infections have been reported in many animals, including prairie dogs, non-human primates, and rats, but the primary reservoir for human infection remains unknown.

Incubation period

Symptomatology and outcome

MPV can cause disease that is clinically indistinguishable from other pox-like illnesses, particularly smallpox. A characteristic 2-day prodrome, manifest by fever and malaise, occurs before development of the rash. Lymphadenopathy (a chronic, abnormal enlargement of the lymph nodes) occurs in many patients 1-2 days before the onset of the rash. Lymphadenopathy is not characteristic of smallpox and is one of the few distinguishing features of human monkeypox. The rash begins as maculopapular lesions of 2-5 mm in diameter and spreads in a centrifugal pattern. The skin lesions progress through papular, vesicular, pustular, and crust phases over a period of 14-21 days. The lesions slough off and leave scars. Monkeypox has a high fatality rate (10%-17%). However, the case-fatality rate for the 2003 outbreak in the United States was 0%.

Prevention and management

There is currently no proven treatment for human monkeypox. Vaccination against smallpox immunizes against monkeypox, but in 1979, the Global Commission for the Certification of Smallpox Eradication concluded that continued smallpox vaccination to prevent human monkeypox was not justified because of the relatively rare occurrence of the disease. Active surveillance programs until the early 1980s contributed to the management of monkeypox. Most recently, an embargo was issued on the importation of African rodents, as a consequence of the 2003 outbreak in the USA. Serial transmission usually does not extend beyond secondary, and that makes it easier to contain outbreaks.