Monkeypox (Mpox)

Reviewed on 7/27/2022

Things to Know About Monkeypox

Monkeypox virus illustration
Symptoms of monkeypox include unexplained acute rash AND one or more of the following symptoms: headache, acute onset of fever (greater than 101.3oF/38.5oC), swollen lymph nodes, muscle and body aches, back pain, and weakness/exhaustion.

Monkeypox facts were written by Charles Patrick Davis, MD, PhD

  • Monkeypox is a rare viral disease, mainly reported in central and western Africa and first discovered in 1958 and has had about 11 outbreaks since then, including one in 2003 in the U.S. There are at least two different genetic types.
  • Signs and symptoms of monkeypox begin with fever, headaches, muscle aches, backache, chills, exhaustion, and swollen lymph nodes followed by the development of pox lesions that form scabs and then fall off.
  • In the U.S. outbreak, pets could have monkeypox symptoms and signs that range from minimal to fever, cough, eye discharge, fatigue, and enlarged lymph nodes that progressed to pox lesions.
  • Monkeypox was first diagnosed by PCR assays from samples taken from a patient with monkeypox symptoms and the patient's pet rodent, a prairie dog.
  • The U. S. stated that in 2003 reported confirmed monkeypox infections were in Illinois, Indiana, Kansas, Missouri, and Wisconsin.
  • Monkeypox first came to the U.S. in a shipment of animals from Ghana that included six different African rodents, several of which were shown to be infected and were housed close to prairie dogs in an Illinois animal pet vendor.
  • Transmission of monkeypox occurs directly or indirectly by contact with an infected human or animal by a viral entrance through broken skin, respiratory tract, or mucous membranes. Also, contaminated droplets, bites or scratches, bush meat preparation, and other contaminated items like rodent bedding are other possible ways the virus may be transmitted.
    • Pregnant people can spread the virus to their fetuses through the placenta.
  • Although there are no proven and safe treatments for monkeypox, health care professionals have used the smallpox vaccine, antivirals, and VIG (vaccinia immune globulin) to control outbreaks.
  • Prevention and/or risk reduction for monkeypox is possible by avoiding direct and indirect contact with individuals, animals, and possibly contaminated items. Health care providers should wear personal protective equipment when caring for patients. Practice good hand hygiene if you may have had contact with any possible contaminated people, animals, or items. Isolate infected patients from others at risk for infection.
  • You can take steps to prevent getting monkeypox and lower your risk during sex.
  • The CDC and ACIP advised investigators, health care workers, lab workers, and anyone who had close or direct contact with people and animals with monkeypox to be vaccinated with the smallpox vaccine (reported to be about 85% cross-protective) up to 14 days after exposure.
  • Health officials in the U.S. (led by the CDC) in the 2003 monkeypox outbreak eventually contained the infection by activating its Emergency Operations Center, deployed personnel to assist state agencies, conducted lab tests, and issued an immediate embargo/prohibition on the sale of certain rodents and prairie dogs. In addition, health care officials issued multiple guidelines for the use of the smallpox vaccine, cidofovir, and vaccinia immune globulin along with guidelines for patient care. Veterinarians, animal control officers, and others were also issued guidelines.
  • The 2003 monkeypox U.S. outbreak was different from most other African outbreaks in that the viral strain introduced to the U.S. was the West African viral type and produces a less severe infection than the Central African monkeypox virus type.
  • 2022 U.S. outbreak, CDC is tracking an outbreak of monkeypox that has spread across several countries that don't normally report monkeypox, including the United States. The total confirmed monkeypox/orthopoxvirus cases increased to more than 3590.

About Monkeypox

Monkeypox is a rare disease that is caused by infection with the monkeypox virus. Monkeypox virus belongs to the Orthopoxvirus genus in the family Poxviridae. The Orthopoxvirus genus also includes variola virus (the cause of smallpox), vaccinia virus (used in the smallpox vaccine), and cowpox virus.

Monkeypox was first discovered in 1958 when two outbreaks of a pox-like disease occurred in colonies of monkeys kept for research, hence the name 'monkeypox.' The first human case of monkeypox was recorded in 1970 in the Democratic Republic of Congo during a period of intensified effort to eliminate smallpox. Since then monkeypox has been reported in humans in other central and western African countries (see table below). The 2003 outbreak in the United States is the only time monkeypox infections in humans were documented outside of Africa.

The natural reservoir of monkeypox remains unknown. However, African rodent species are expected to play a role in transmission.

There are two distinct genetic groups (clades) of monkeypox virus -- Central African and West African. West African monkeypox is associated with milder disease, fewer deaths, and limited human-to-human transmission.

Monkeypox Outbreak Global Chart
Count Years Recorded Human Cases
Cameroon 1976
The Central African Republic 1984 6
Democratic Republic of Congo Endemic
Gabon 1987
Ivory Coast 1971
Liberia 1970 4
Nigeria 1971
Republic of Congo Sporadic
Sierra Leone 1970
Sudan 2005 19
United States 2003 47


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Signs and Symptoms of Mokeypox

In humans, the symptoms of monkeypox are similar to but milder than the symptoms of smallpox. Monkeypox begins with fever, headache, muscle aches, and exhaustion. The main difference between the symptoms of smallpox and monkeypox is that monkeypox causes lymph nodes to swell (lymphadenopathy) while smallpox does not. The incubation period (time from infection to symptoms) for monkeypox is usually 7-14 days but can range from 5-21 days.

The illness begins with:

  • Fever
  • Headache
  • Muscle aches
  • Backache
  • Swollen lymph nodes
  • Chills
  • Exhaustion

Within 1 to 3 days (sometimes longer) after the appearance of fever, the patient develops a rash, often beginning on the face and then spreading to other parts of the body.

Lesions progress through the following stages before falling off:

  • Macules
  • Papules
  • Vesicles
  • Pustules
  • Scabs

The illness typically lasts for 2-4 weeks. In Africa, monkeypox has been shown to cause death in as many as 1 in 10 persons who contract the disease.

What Signs and Symptoms Were Seen in Pets?

During the U.S. outbreak, illnesses in animals included fever, cough, discharge from the eyes, and enlarged lymph nodes, accompanied by the development of lesions. Animals that had monkeypox also appeared to be very tired and were not eating or drinking. Some animals had only minimal signs of illness and recovered, while others died.

How Was Monkeypox First Diagnosed in the United States?

The clinical features of the illness in U.S. patients -- fever, headache, muscle aches, and rash -- were consistent with those of monkeypox. Initially, scientists at the Marshfield Clinic in Marshfield, Wisconsin, recovered a virus resembling a poxvirus from one of the first patients and the patient's pet prairie dog. Laboratory tests at CDC -- including several PCR-based assays looking for poxvirus DNA, electron microscopy, and gene sequencing -- confirmed that the agent causing the illnesses were the monkeypox virus.

Which States Were Affected by the Outbreak?

Forty-seven confirmed and probable cases of monkeypox were reported from six states -- Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin -- during the 2003 U.S. outbreak.  As of July 26, 2022, the total confirmed monkeypox/orthopoxvirus cases increased to 3591.

U.S. Monkeypox Cases by State, 2003
State Confirmed Cases Probable Cases
Illinois 9 1
Indiana 7 3
Kansas 1 0
Missouri 2 0
Wisconsin 18 6
Total 37 10

How Was Monkeypox Virus Introduced into the U.S.?

Investigators determined that a shipment of animals from Ghana, imported to Texas on April 9, 2003, introduced the monkeypox virus into the United States. The shipment contained approximately 800 small mammals representing nine different species, including six genera of African rodents. These rodents included rope squirrels (Funiscuirus sp.), tree squirrels (Heliosciurus sp.), African giant pouched rats (Cricetomys sp.), brush-tailed porcupines (Atherurus sp.), dormice (Graphiurus sp.), and striped mice (Lemniscomys sp.). CDC laboratory testing using PCR and virus isolation demonstrated that two African giant pouched rats, nine dormice, and three rope squirrels were infected with monkeypox virus. After importation into the United States, some of the infected animals were housed in close proximity to prairie dogs at the facilities of an Illinois animal vendor. These prairie dogs were sold as pets prior to their developing signs of infection.

Transmission of Monkeypox

  • Transmission of monkeypox virus occurs when a person comes into contact with the virus from an animal, human, or materials contaminated with the virus.
  • The virus enters the body through broken skin (even if not visible), respiratory tract, or mucous membranes (eyes, nose, or mouth). Animal-to-human transmission may occur by bite or scratch, bush meat preparation, direct contact with body fluids or lesion material, or indirect contact with lesion material, such as through contaminated bedding.
  • Human-to-human transmission is thought to occur primarily through large respiratory droplets.
  • Respiratory droplets generally cannot travel more than a few feet, so prolonged face-to-face contact is required.
  • Other human-to-human methods of transmission include direct contact with body fluids or lesion material, and indirect contact with lesion material, such as through contaminated clothing or linens.

The reservoir host (main disease carrier) of monkeypox is still unknown although African rodents are suspected to play a part in transmission. The virus that causes monkeypox has only been recovered (isolated) twice from an animal in nature. In the first instance (1985), the virus was recovered from an apparently ill African rodent (rope squirrel) in the Equateur Region of the Democratic Republic of Congo. In the second (2012), the virus was recovered from a dead infant mangabey found in the Tai National Park, Cote d'Ivoire.

Treatment for Monkeypox

There are no treatments specifically for monkeypox virus infections. However, monkeypox and smallpox viruses are genetically similar, which means that antiviral drugs and vaccines developed to protect against smallpox may be used to prevent and treat monkeypox virus infections.

Antivirals, such as tecovirimat (TPOXX), may be recommended for people who are more likely to get severely ill, like patients with weakened immune systems.

If you have symptoms of monkeypox, you should talk to your healthcare provider, even if you don’t think you had contact with someone who has monkeypox.

Prevention Steps

Take the following steps to prevent getting monkeypox:

  • Avoid close, skin-to-skin contact with people who have a rash that looks like monkeypox.
    • Do not touch the rash or scabs of a person with monkeypox.
    • Do not kiss, hug, cuddle or have sex with someone with monkeypox.
    • Do not share eating utensils or cups with a person with a monkeypox.
  • Do not handle or touch the bedding, towels, or clothing of a person with monkeypox.
  • Wash your hands often with soap and water or use an alcohol-based hand sanitizer.
  • In Central and West Africa, avoid contact with animals that can spread the monkeypox virus, usually rodents and primates. Also, avoid sick or dead animals, as well as bedding or other materials they have touched.

If you are sick with monkeypox:

  • Isolate at home
  • If you have an active rash or other symptoms, stay in a separate room or area away from people or pets you live with, when possible.


CDC recommends vaccination for people who have been exposed to monkeypox and people who are at higher risk of being exposed to monkeypox, including:

  • People who have been identified by public health officials as in contact with someone with monkeypox
  • People who may have been exposed to monkeypox, such as:
    • People who are aware that one of their sexual partners in the past 2 weeks has been diagnosed with monkeypox
    • People who had multiple sexual partners in the past 2 weeks in an area with known monkeypox
  • People whose jobs may expose them to orthopoxviruses, such as:
    • Laboratory workers who perform testing for orthopoxviruses
    • Laboratory workers who handle cultures or animals with orthopoxviruses
    • Some designated healthcare or public health workers


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How Was the Outbreak Contained?

CDC and the public health departments in the affected states, together with the U.S. Department of Agriculture, the Food and Drug Administration, and other agencies, participated in a variety of activities that prevented the further spread of monkeypox. To assist with the investigation and outbreak response, CDC took the following steps:

  • Activated its Emergency Operations Center.
  • Deployed teams of medical officers, epidemiologists, and other experts to several states to assist with the investigation.
  • Conducted extensive laboratory testing on specimens from humans and animals thought to have been exposed to monkeypox.
  • Issued interim U.S. case definitions for human monkeypox and for animal monkeypox.
  • Issued interim guidelines on infection control and exposure management for patients in the health care and community settings.
  • Issued an immediate embargo and prohibition on the importation, interstate transportation, sale, and release into the environment of certain rodents and prairie dogs.
  • Provided ongoing assistance to state and local health departments in investigating possible cases of monkeypox in both humans and animals in the United States.
  • Worked with state and federal agencies to trace the origin and distribution of potentially infected animals.
  • Issued interim guidance on the use of smallpox vaccine, cidofovir, and vaccinia immune globulin in the setting of an outbreak of monkeypox.
  • Issued interim guidelines for veterinarians.
  • Issued interim guidance for persons who have frequent contact with animals, including pet owners, pet shop employees, animal handlers, and animal control officers.

How Was the U.S. Monkeypox Outbreak Different From Outbreaks That Have Occurred in Africa?

Studies of monkeypox virus suggest that there are at least 2 different genetic types (clades) of the virus. Virus clades segregate based upon geographic separation, with one type being found in West Africa and the other in Central Africa. The strain introduced into the U.S. came from Ghana, located in West Africa. Human infections with Central African monkeypox virus are typically more severe than infections with the West African virus type. Person-to-person spread of monkeypox viruses occurs, and has been well-documented for Central African type of virus.

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Monkeypox Sign

Swollen Lymph Nodes

Lymph nodes (erroneously called lymph glands) are a part of the lymphatic system, a component of the body's immune system. Swollen lymph nodes may signal an infection.

There are several groups of lymph nodes, which are small, bean-shaped, soft nodules of tissue. The ones most frequently enlarged or swollen are found in the neck (a chain of lymph nodes is located in the front of the neck, the sides of the neck, and the back of the neck behind the ears), under the chin, in the armpits, and in the groin. There is also a large group of lymph nodes in the chest and abdomen, which are sometimes found to be enlarged on X-rays or CT scans.

Reviewed on 7/27/2022

United States. Centers for Disease Control and Prevention. "About Monkeypox." July 22, 2022. <>.

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