Human infections with monkeypox virus, from the genus Orthopoxvirus, were first observed in West and Central Africa during the early 1970s, after smallpox had already been eradicated in this region. Although the signs and symptoms of monkeypox are very similar to those of smallpox, this virus is significantly different.
The epidemiology of monkeypox is completely different from that of smallpox. Firstly, this virus is a rare zoonosis found only in the small villages of the tropical rain forests of western and central Africa, with cases mostly reported in Zaire. As a result of intensive surveillance efforts conducted by the World Health Organization, only 400 cases were reported worldwide from the time infection by monkeypox virus was first observed in 1970 to the time when surveillance ceased in 1986.
Monkeypox virus is believed to be transmitted through direct contact with wild animals killed for food, such as squirrels and monkeys. A very important feature of monkeypox is that person-to-person transmission is rare, accounting for less than 1/3 of observed cases.
Incubation period is between 10-14 days, usually 12 days.
Clinical Features and Outcomes
The clinical features are almost indistinguishable from those of ordinary-type smallpox, with the exception of the enlargement of cervical and inguinal lymph nodes.
Like ordinary-type small pox, monkeypox virus produces a generalized pustular rash with smaller lesions, a fever, and minor toxemia. It also has a healing period that progresses more rapidly.
Pathogenesis and Pathology
The pathogenesis of human monkeypox is very similar to that of smallpox, with the exception that viral entry from a wildlife source probably occurs via small lesions on the skin or oral mucous membranes. Viral entry may also occur via the respiratory tract in the rare cases of person-to-person transmission.
Like smallpox, monkeypox virus replicates in lymphoid tissue, although it has a greater degree of lymphadenopathy. The virus first localizes in mononuclear phagocytic cells, is released into the bloodstream, and then localizes again in skin cells. For more detailed information, please refer to the pathogenesis section of smallpox virus.
Prevention and Management
Vaccination with smallpox vaccine immunizes against monkeypox, but it is not justified since the disease is so rare. In the United States, vaccinia vaccination is recommended for laboratory workers who directly handle cultures or animals infected with monkeypox virus.
Management for monkeypox involves effective surveillance efforts such as those undertaken by the World Health Organization prior to 1980. An important thing to remember is that unlike smallpox, human monkeypox has a lower capacity for human spread. This makes identification and containment much more accessible.