Human monkeypox is a rare zoonotic viral disease that occurs primarily in remote villages of Central and Western Africa close to tropical rainforests where there is frequent contact with infected animals. Monkeypox is usually transmitted to humans from rodents, pets and primates through contact with the animal's blood or through a bite.
Monkeypox was first associated with human illness in Zaire and West Africa during 1970-1971. A second outbreak of human illness was identified in Zaire in 1996-1997. As of 2003, a small outbreak of human monkeypox in the United States appears to be in progress.
Symptoms and disease course
In humans, monkeypox is similar to smallpox, although it is often milder. Unlike smallpox, monkeypox causes lymph nodes to swell (lymphadenopathy). The incubation period for monkeypox is about 12 days (range 7 to 17 days). The illness begins with fever, headache, muscle aches, backache, swollen lymph nodes, a general feeling of discomfort, and exhaustion. Within 1 to 3 days (sometimes longer) after the appearance of fever, the patient develops a papular rash (i.e., raised bumps), often first on the face but sometimes initially on other parts of the body. The lesions usually develop through several stages before crusting and falling off.
Vaccination against smallpox, which is no longer necessary, also gives protection against the monkeypox virus. Limited person-to-person spread of infection has been reported in disease-endemic areas in Africa. Case-fatality ratios in Africa have ranged from 1% to 10% (for additional information about monkeypox, see  ).
Prevention and treatment
Currently, there is no proven, safe treatment for monkeypox. Smallpox vaccine has been reported to reduce the risk of monkeypox among previously vaccinated persons in Africa. The United States Centers for Disease Control and Prevention (CDC) recommends that persons investigating monkeypox outbreaks and involved in caring for infected individuals or animals should receive a smallpox vaccination to protect against monkeypox. Persons who have had close or intimate contact with individuals or animals confirmed to have monkeypox should also be vaccinated. These persons can be vaccinated up to 14 days after exposure. CDC does not recommend preexposure vaccination for unexposed veterinarians, veterinary staff, or animal control officers, unless such persons are involved in field investigations.
Recent U.S. outbreak
As of June 7, 2003, cases of suspected monkeypox in the United States had been reported among residents of Wisconsin (18), northern Illinois (10), and northwestern Indiana (1). The disease stemmed from a giant Gambian pouch rat imported by a pet shop in Chicago and is believed to have infected domesticated prairie dogs, which were then distributed by other outlets in the Midwest. Electron microscopy and serologic studies were used to confirm that the disease was human monkeypox.
As of June 11, a total of 54 persons with suspected monkeypox had been reported in Wisconsin (20), Illinois (10), Indiana (23), and New Jersey (1). Monkeypox had been confirmed by laboratory tests in nine persons. At least 14 of the people with suspected monkeypox had been hospitalized for their illness; there have been no deaths related to the outbreak. The number of cases and states involved in the outbreak will likely change as the investigation continues. The CDC Web site has updates for this and other current information about the outbreak.
The onset of illness among patients in the United States began in early May 2003. Patients typically experienced a prodrome consisting of fever, headaches, myalgias, chills, and drenching sweats. Roughly one-third of patients had nonproductive cough. This prodromal phase was followed 1-10 days later by the development of a papular rash that typically progressed through stages of vesiculation, pustulation, umbilication, and crusting. In some patients, early lesions have become ulcerated. Rash distribution and lesions have occurred on head, trunk, and extremities; many of the patients had initial and satellite lesions on palms and soles and extremities. Rashes were generalized in some patients. After onset of the rash, patients have generally manifested rash lesions in different stages. All patients reported direct or close contact with prairie dogs, most of which were sick. Illness in prairie dogs was frequently reported as beginning with a blepharoconjunctivitis, progressing to presence of nodular lesions in some cases. Some prairie dogs have died from the illness, while others reportedly recovered.
Despite reports in June 2003 of possible human-to-human spread of Monkeypox in the U.S.(consistent with the history of the disease in Africa, see external links), there has never been a documented or laboratory-confirmed case of human-to-human spread of the disease.
- CDC Questions and Answers About Monkeypox
- CDC - Human Monkeypox -- Kasai Oriental, Zaire, 1996-1997
- CDC - Outbreak of Human Monkeypox, Democratic Republic of Congo, 1996 to 1997
- CDC Preliminary Report: Multistate Outbreak of Monkeypox in Persons Exposed to Pet Prairie Dogs
- National Library of Medicine - Monkeypox virus
Note: much of the original text of this article is taken from public domain CDC (Center for Disease Control) and NIH (National Institute of Health) sources.