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FACT SHEET Basic Information About Monkeypox

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Monkeypox: An Emerging Infectious Disease in North America

Monkeypox is a rare viral disease that is found mostly in the rainforest countries of central and west Africa. The disease is called “monkeypox” because it was first discovered in laboratory monkeys in 1958. Blood tests of animals in Africa later found evidence of monkeypox infection in various rodent species. The virus that causes monkeypox was recovered from an African squirrel, which may be the natural host. Laboratory studies showed that the virus could also infect rats, mice, and rabbits.

In 1970, monkeypox was identified as the cause of a rash illness in humans in remote African locations. In early June 2003, monkeypox was reported among several residents in the United States who became ill after having contact with sick pet prairie dogs. This is the first evidence of community-acquired monkeypox in the United States.

Cause of Monkeypox

The disease is caused by Monkeypox virus, which belongs to the orthopoxvirus group of viruses. Other orthopoxviruses that can cause infection in humans include variola (smallpox), vaccinia (used in smallpox vaccine), and cowpox viruses.

Signs and Symptoms

In humans, the signs and symptoms of monkeypox are similar to those of smallpox, but usually milder. Unlike smallpox, monkeypox causes swollen lymph nodes. The incubation period for monkeypox is about 12 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 onset 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. The illness typically lasts for 2 to 4 weeks. In Africa, monkeypox is fatal in as many as 10% of people who get the disease; the case fatality ratio for smallpox was about 30% before the disease was eradicated.

Spread of Monkeypox in Humans

People can get monkeypox from an infected animal through a bite or direct contact with the infected animal’s blood, body fluids, or lesions. The disease also can be spread from person to person, but it is much less infectious than smallpox. The virus is thought to be transmitted by large respiratory droplets during direct and prolonged face-to-face contact. In addition, monkeypox can be spread by direct contact with body fluids of an infected person or with virus-contaminated objects, such as bedding or clothing.

Treatment and Prevention

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. CDC is recommending 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 is not recommending preexposure vaccination for unexposed veterinarians, veterinary staff, or animal control officers, unless such persons are involved in field investigations.

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Page last modified September 5, 2008

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