Monkeypox is a rare infectious disease caused by monkeypox virus. The disease was first identified in laboratory monkeys, giving it its name. The disease is most prevalent in Central and West Africa, but an outbreak occurred also in the United States in 2003. Monkeypox can be difficult to distinguish from mild smallpox and chickenpox.

Human monkeypox is a zoonotic viral disease that occurs primarily in remote villages of Central and West Africa in proximity to tropical rainforests where there is more 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.


In addition to monkeys, giant pouched rats (Cricetomys sp.), dormice (Graphiurus sp.) and African squirrels (Heliosciurus, Funisciurus) have all been implicated as reservoirs of the virus. The use of these animals as food may be an important means of transmission to humans.

Monkeypox as a disease 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. In 2003, a small outbreak of human monkeypox in the United States occurred among owners of pet prairie dogs. The prairie dogs had been exposed to an infected Gambian pouched rat (Cricetomys gambianus).

A second African focus of infection has been discovered in Sudan.

Monkeypox disease in animals

The symptoms of a sick animal include: listlessness, ocular and nasal discharges, cough, hair loss sometimes accompanied by scabs, and pneumonia. Look for nodules similar to mosquito bites and inflammation of the lymph glands.

Monkeypox disease in humans

Symptoms and 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.

It is assumed that Vaccination against smallpox would provide protection against human monkeypox infection considering that they are closely related viruses and the vaccine protects animals from experimental lethal monkeypox challenge . This has not been conclusively demonstrated in humans because routine smallpox vaccination was discontinued following the eradication of smallpox due to safety concerns with the vaccine. 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%.

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.

2003 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 Texas that 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.

By June 9, CDC officials said the number of suspected or confirmed cases was 22 in Wisconsin, 10 in Indiana, and five in Illinois.

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 were no deaths related to the outbreak.

The onset of the illness among the 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 had become ulcerated. Rash distribution and lesions occurred on head, trunk, and extremities; many of the patients had initial and satellite lesions on palms, soles, and extremities. Rashes were generalized in some patients. After onset of the rash, patients 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 died from the illness, while others reportedly recovered.


External links

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.

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