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Monkeypox

Fact sheet N°161
February 2011


Key facts

  • The monkeypox virus can cause a fatal disease in humans; it is similar to human smallpox, although typically much less serious.
  • Monkeypox occurs primarily in remote villages in Central and West Africa, near tropical rainforests.
  • The monkeypox virus is transmitted to people from a variety of wild animals and it spreads in human population through human-to-human transmission.
  • There is no treatment or vaccine available although smallpox vaccination has proven to be 85% effective in preventing monkeypox.

Monkeypox is a viral zoonosis with symptoms in humans similar to those seen in the past in smallpox patients. However, smallpox no longer occurs, following its worldwide eradication in 1980, whereas monkeypox still occurs sporadically in parts of Africa.

Monkeypox is a member of the Orthopoxvirus genus in the family Poxviridae.

The virus was first identified in the State Serum Institute in Copenhagen, Denmark, in 1958 during an investigation into a pox-like disease among monkeys.

Outbreaks

Human monkeypox was first identified in humans in 1970 in the Democratic Republic of Congo. Since then, the majority of cases have been reported in rural regions of the Congo Basin and western Africa, particularly in the Democratic Republic of Congo. In 1996-97, a major outbreak occurred in the Democratic Republic of Congo. In the spring of 2003, monkeypox cases were confirmed in the Midwest of the United States of America, marking the first reported occurrence of the disease outside of the African continent. More recently, monkeypox has been reported in Unity, Sudan.

Transmission

Infections of index cases result from direct contact with the blood, bodily fluids, or rashes of infected animals. In Africa, human infections have been documented through the handling of infected monkeys, Gambian rats or squirrels.

Secondary transmission is human-to-human, resulting from close contact with infected respiratory tract excretions, with the skin lesions of an infected person or with recently contaminated objects. Transmission via droplet respiratory particles has also been documented. Transmission can also occur by inoculation or via the placenta (congenital monkeypox). There is no evidence to date that person-to-person transmission alone can sustain monkeypox in the human population.

Signs and symptoms

The incubation period (interval from infection to onset of symptoms) of monkeypox varies from 6 to 16 days.

The infection can be divided into two periods:

  • the invasion period (0-5 days) characterized by fever, intense headache, lymphadenopathy (swelling of the lymph node), back pain, myalgia (muscle ache) and an intense asthenia (lack of energy);
  • the skin eruption period where the various stages of the eruption appear on the face (in 95% of cases), on the palms of the hands and soles of the feet (75%) and on the body nearly simultaneously. Evolution of the rash from maculopapules (lesions with a flat bases) to vesicles (small fluid-filled blisters), pustules, followed by crusts occurs in approximately 10 days. Three weeks might be necessary before the complete elimination of the crusts.

The number of the lesions varies from a few to several thousand, affecting oral mucous membranes (in 70% of cases), genitalia (30%), and conjunctivae (eyelid) (20%), as well as the cornea (eyeball).

Some patients develop severe lymphadenopathy (swollen lymph nodes) before the appearance of the rash. The presence of lymphadenopathy can help identify the disease as monkeypox since it is not characteristic of either smallpox or chickenpox.

The symptoms of monkeypox usually last from 14 to 21 days.

The case fatality has varied widely between epidemics but, has been less than 10% in documented cases. Most fatalities occur in young children. In addition, children may be more susceptible to monkeypox due to the termination of regular smallpox vaccinations following the worldwide eradication of the disease in 1980.

Diagnosis

The differential diagnoses include usually smallpox, chickenpox, measles, bacterial skin infections, scabies, medicamentous allergies and syphilis.

Monkeypox can only be diagnosed definitively in the laboratory where the infection can be diagnosed by a number of different tests:

  • enzyme-linked immunosorbent assay (ELISA)
  • antigen detection tests
  • polymerase chain reaction (PCR) assay
  • virus isolation by cell culture.

Treatment and vaccine

There are no drugs or vaccines available for monkeypox, although vaccination against smallpox has been proven to be 85% effective in preventing monkeypox in the past.

Natural host of monkeypox virus

In Africa, monkeypox infection has been found in many animal species: rope squirrels, tree squirrels, Gambian rats, striped mice, doormice and primates. Doubts persist on the natural history of the virus and further studies are needed to identify the exact reservoir of the monkeypox virus and how it is maintained in nature.

In the USA, the virus is thought to have been transmitted from African animals to a number of susceptible non-African species (like prairie dogs) with which they were co-housed.

Prevention

Preventing monkeypox expansion through animal trade

Restricting or banning the movement of small African mammals and monkeys may be effective in slowing the expansion of the virus outside Africa.

Captive animals should not be inoculated against smallpox. Instead, infected animals should be isolated from other animals and placed into immediate quarantine. Any animals that might have come into contact with an infected animal should be quarantined and observed for monkeypox symptoms for 30 days.

Reducing the risk of infection in people

During monkeypox outbreaks, close contact with other patients is the most significant risk factor for monkeypox virus infection. In the absence of specific treatment and a vaccine, the only way to reduce infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to the virus.

Public health educational messages should focus on the following risks.

  • Reducing the risk of human-to-human transmission. Close physical contact with monkeypox infected people should be avoided. Gloves and protective equipment should be worn when taking care of ill people. Regular hand washing should be carried out after caring for or visiting sick people.
  • Reducing the risk of animal-to-human transmission. Efforts to prevent transmission in endemic regions should focus on thoroughly cooking all animal products (blood, meat) before eating. Gloves and other appropriate protective clothing should be worn while handling sick animals or their infected tissues, and during slaughtering procedures.
Controlling infection in health-care settings

Health-care workers caring for patients with suspected or confirmed monkeypox virus infection, or handling specimens from them, should implement standard infection control precautions (see the "Related links" section for more information on "standard precautions in health care").

Healthcare workers and those treating or exposed to patients with monkeypox or their samples should consider being immunized against smallpox. However, the smallpox vaccination should not be administered to people with comprised immune systems.

Samples taken from people and animals with suspected monkeypox virus infection should be handled by trained staff working in suitably equipped laboratories.

WHO response

WHO country offices are supporting surveillance and outbreak response activities in affected countries.

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