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Monkeypox is an infectious disease caused by an orthopoxvirus. Orthopoxviruses are a genus of viruses that include the disease agents that cause human smallpox, cowpox, and camelpox as well as monkeypox. Monkeypox, which was first identified in humans in an outbreak in Africa in 1970, usually produces a less severe illness with fewer fatalities than smallpox. However, its symptoms are similar: fever, pus-filled blisters all over the body, and respiratory problems.
Monkeypox is classified as a zoonosis, which means that it is a disease of animals that can be transmitted to humans under natural conditions. The first cases of monkeypox reported in humans involved contact between humans and animals in the African rain forest. The outbreak that made headlines in the United States in June 2003, however, involved animals purchased as pets from pet stores. In nature, monkeypox has been found in monkeys, chimpanzees, rabbits, prairie dogs, Gambian rats, ground squirrels, and mice. It is not known as of late 2003 whether other wild or domestic animals can contract monkeypox.


Prior to 2003, most monkeypox cases were diagnosed in remote areas of central and west Africa. Between February 1996 and October 1997, however, there were 511 suspected cases of monkeypox in the Democratic Republic of the Congo (DRC, formerly Zaire). This outbreak, the largest ever, raised fears that the virus had mutated and become more infectious.
In late 1997, the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) announced that this relatively large outbreak was likely due to human behavior, rather than virus mutation. During the outbreak, the DRC was embroiled in civil war. Food shortages increased reliance on hunting and raised chances that people would come into contact with infected animals.
The 2003 outbreak in the United States, which was the first confirmed instance of community-acquired monkeypox in North America, came to the attention of the CDC in early June, when a laboratory in Wisconsin identified the monkeypox virus in samples taken from the skin of an infected patient and lymph node tissue from the patient's pet prairie dog. By the end of June, cases of monkeypox in humans had been identified in six Midwestern states (Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin). The patients acquired the virus from infected prairie dogs purchased as pets, which in turn were infected through contact with animals imported from Africa that were sold in the same pet stores.
Monkeypox is less severe than smallpox and can sometimes be confused with chickenpox. It seems partly preventable with smallpox vaccination, but vaccination programs were discontinued in the late 1970s. (Barring samples stored in laboratories, smallpox has been eradicated.) People under the age of 16—those born after smallpox vaccination ended—seem the most susceptible to monkeypox. During the 1996–97 outbreak, approximately 85% of the cases were in this age group.
Although the monkeypox virus is related to the smallpox virus, experts do not think (as of late 2003) that it is likely to be cultivated as an agent of bioterrorism. Monkeypox is much less easily transmitted person-to-person than smallpox and has a much lower fatality rate.

Causes and symptoms

The monkeypox virus is transmitted to humans through an infected animal's blood, body sores, or bite; or through handling an infected animal's bedding or cage. Initial symptoms of monkeypox in humans include fever, a bodywide rash (exanthem) of pus-filled blisters, and flu-like muscle aches and fatigue. These symptoms can be accompanied by diarrhea, swollen lymph nodes, a sore throat, and mouth sores. In some cases, a victim may experience trouble breathing. Symptoms are at their worst for 3-7 days, after which the fever lessens and blisters begin to form crusts.
The symptoms of monkeypox in pet rabbits, rats, or mice include inflammation of the eyes, a nasal discharge, fever, loss of appetite, a skin rash, and tiredness. Pet monkeys typically develop a rash with pus-filled lesions on the palms of the hands, trunk, and tail. They may also have mouth ulcers.


Since the symptoms of monkeypox resemble other diseases caused by orthopox viruses, definitive diagnosis may require laboratory testing to uncover the virus or evidence (from antibodies in the blood) that it is present. As of 2003, laboratory techniques that can be used to identify the monkeypox virus include electron microscopy, polymerase chain reaction (PCR), immunohistochemistry, and ELISA testing.


Like most viruses, monkeypox cannot be resolved with medication. The only treatment option is symptomatic—that is, patients are made as comfortable as possible. In March 1998, the U.S. Army Medical Research Institute for Infectious Diseases reported that an antiviral drug called cidofovir may combat monkeypox infection. As of 2003, additional studies report that cidofovir appears to be safe and effective as a treatment for monkeypox in humans. The drug has worked successfully in primates, but further research is needed to determine its effectiveness in humans.


Children are more likely to contract the disease and have the highest death rate. Monkeypox is not as lethal as smallpox, but the death rate among young children may reach 2-10%. In some cases, hospitalization is required. Recovery is good among survivors, although some scarring may result from the blisters.


Monkeypox is one of the diseases that physicians, veterinarians, and public health officials are required by law to report to the CDC.
Although smallpox vaccination offers some protection against monkeypox, experts do not generally recommend getting a smallpox vaccination simply to guard against monkeypox if one has not been exposed to it. However, the CDC recommends as of June 2003 that anyone who has had close contact with humans or animals infected with monkeypox, or has helped to care for them, should be vaccinated against smallpox. The vaccination can be administered as late as 14 days after exposure to the virus. In addition, veterinarians or public health personnel conducting field investigations should be vaccinated before any exposure to monkeypox.
As of late 2003, no cases of monkeypox were identified in cats or dogs belonging to people infected by the June outbreak. The American Veterinary Medicine Association (AVMA) recommends, however, that cats, dogs, or other mammals that have been in contact with an animal known to have monkeypox should be kept in quarantine for 30 days from the date of exposure.
People who have a pet with symptoms of monkeypox should not take it to an animal shelter or release it into the wild. They should isolate it from humans and other animals, and take it to a veterinarian in a closed, chew-proof container with air holes.
On June 11, 2003, the CDC and the Food and Drug Administration (FDA) issued a joint order prohibiting the importation of rats and other rodents from Africa. In addition, the agencies banned the sale and distribution of prairie dogs and six species of African rodents in the United States.



Altman, Larry K., MD, and Jodi Wilgoren. "20 Cases of Disease Related to Smallpox Detected in the U.S." New York Times June 9, 2003.
Centers for Disease Control and Prevention. "Multistate Outbreak of Monkeypox—Illinois, Indiana, and Wisconsin, 2003." Morbidity and Mortality Weekly Report 52 (June 13, 2003): 537-540.
Centers for Disease Control and Prevention. "Update: Multistate Outbreak of Monkeypox—Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin, 2003." Morbidity and Mortality Weekly Report 52 (June 20, 2003): 561-564.
Centers for Disease Control and Prevention. "Update: Multistate Outbreak of Monkeypox—Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin, 2003." Morbidity and Mortality Weekly Report 52 (June 27, 2003): 589-590.
Rosen, T., and J. Jablon. "Infectious Threats from Exotic Pets: Dermatological Implications." Dermatologic Clinics 21 (April 2003): 229-236.
Smee, D. F., K. W. Bailey, and R. W. Sidwell. "Comparative Effects of Cidofovir and Cyclic HPMPC on Lethal Cowpox and Vaccinia Virus Respiratory Infections in Mice." Chemotherapy 49 (June 2003): 126-131.


American Veterinary Medical Association (AVMA). 1931 North Meacham Road, Suite 100, Schaumburg, IL 60173-4360.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311.


American Veterinary Medical Association (AVMA). "Foreign Animal Disease Alert: Investigation Uncovers First Outbreak of Monkeypox Infection in the Western Hemisphere," June 23, 2003.
American Veterinary Medical Association (AVMA). Monkeypox Backgrounder. Schaumburg, IL: AVMA, June 2003.
Centers for Disease Control and Prevention (CDC). Fact Sheet: Basic Information About Monkeypox. Atlanta, GA: CDC, June 2003.
Centers for Disease Control and Prevention (CDC). Fact Sheet: Embargoed Animals and Monkeypox Virus. Atlanta, GA: CDC, June 2003.

Key terms

Antiviral — Refers to a drug that can destroy viruses and help treat illnesses caused by them.
Bioterrorism — The intentional use of diseasecausing microbes or other biologic agents to intimidate or terrorize a civilian population for political or military reasons.
Mutation — A change in an organism's genetic code that causes it to develop new characteristics.
Orthopoxvirus — The genus of viruses that includes monkeypox, smallpox, cowpox, and camelpox.
Symptomatic — Refers to treatment that addresses the symptoms of an illness, but not its underlying cause.
Zoonosis (plural, zoonoses) — Any disease of animals that can be transmitted to humans under natural conditions. Monkeypox is a zoonosis.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


A disease of monkeys and, rarely, of humans, caused by the monkeypox virus, a member of the family Poxviridae; the human disease is serious and clinically resembles smallpox. An outbreak was recorded in the U.S. midwest in 2003 that was derived from a vector in prairie dogs infected by proximity to a giant rat of the Gambia in a pet shop.
Farlex Partner Medical Dictionary © Farlex 2012


An infectious disease caused by a poxvirus that occurs mostly in the tropical rain forests of central and western Africa, is transmitted from wild animals killed for food, such as monkeys and squirrels, and causes symptoms similar to but milder than smallpox.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A rare smallpoxlike disease caused by the monkeypox virus transmitted by exposure to infected prairie dogs or giant rats of the Gambia. Transmission can also occur by contact with a human patient. The incubation period is 12 days; the disease and is characterized by rash and may include chills and sweats, headache, backache, lymphadenopathy, sore throat, cough, and shortness of breath. Smallpox vaccine has been reported to reduce the risk of monkeypox among people previously vaccinated.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


A disease of primates in Central Africa caused by a virus similar to the virus that caused the now eradicated SMALLPOX. Some cases have been transmitted from monkeys to humans
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005