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Monkeypox in Adult
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Monkeypox in Adult

Contributors: Paritosh Prasad MD, Edith Lederman MD, Susan Burgin MD
Other Resources UpToDate PubMed


Updated May 29, 2022. Refer to US Centers for Disease Control and Prevention (CDC) (Information for Clinicians) for the most current information. See Diagnostic Pearls section for the CDC case definitions.

As of May 25, 2022, clusters of monkeypox have been reported in at least 19 countries where the disease is not usually endemic: 229 confirmed cases have been identified in Australia, Austria, Belgium, Canada, Czech Republic, Denmark, France, Germany, Israel, Italy, Netherlands, Portugal, Slovenia, Spain, Sweden, Switzerland, United Arab Emirates, the United Kingdom (England and Scotland), and the United States; at least 88 more cases are suspected, including in additional countries (Argentina, Finland).

Clinical features:
The incubation period of monkeypox is approximately 12 days (7-14 day range usually, but can be 5-21 days). Monkeypox begins with a prodrome of fever, headache, malaise, backache, lymphadenopathy, chills, nonproductive cough, and arthralgias followed 1-10 days later (usually by day 3) by the development of a papular, vesicular, then pustular eruption on the face, trunk, and extremities. Some patients also experience myalgias, nausea and vomiting, lethargy, sore throat, dyspnea, and sweats.

The clinical presentation is similar to but milder than that of smallpox, with the primary difference being that individuals with monkeypox develop lymphadenopathy, whereas those with smallpox do not. Illness typically lasts 2-4 weeks.

The CDC advises clinicians to be alert for symptoms associated with monkeypox, including the distinctive rash, even in the absence of fever or other flu-like symptoms; onset of perianal or genital lesions in the absence of subjective fever has been reported.

Although human-to-human transmission historically has been rare, the cases in 2022 suggest community transmission occurring through close contact, ie, large respiratory droplets, direct contact with skin lesions or bodily fluids, or indirect contact via contaminated clothing or linens. The World Health Organization (WHO) notes that anyone who has had close physical contact with someone with monkeypox is at risk of contracting the virus, and there is a high likelihood that further cases with unidentified chains of transmission will be identified. Men who have sex with men may be at higher risk for infection.

A WHO surveillance program from 1981 to 1986 in the Democratic Republic of the Congo [the former Zaire] reported an R-naught (R0) < 1 and that human-to-human transmission was at low enough levels as to not present a significant public health risk. (R0 represents, on average, the number of people to whom a single infected person can be expected to transmit that disease.) It remains to be seen if the R0 of the 2022 outbreak is different from this prior finding.

The longest chain of infection identified in these studies was 4 generations, although in more recent African outbreaks, this has risen to 6-9 generations; again, it is unclear how applicable this is to the 2022 outbreak.

The secondary attack rate of monkeypox in unvaccinated contacts was 9.3% compared with 37%-88% for smallpox (so much less infectious).

About Monkeypox
Monkeypox is a rare zoonotic Orthopoxvirus infection that is clinically similar to smallpox. Human monkeypox had been limited to the rain forest areas of Central and West Africa (principally the Democratic Republic of the Congo and the Republic of the Congo) until June 2003, when cases were first reported in Wisconsin, Illinois, and northwestern Indiana. This 2003 outbreak was associated with exposure to pet prairie dogs which had been housed near imported small mammals from Ghana. Infection had not been observed in the Western Hemisphere until this time.

In Africa, the disease affects people who have hunted or eaten squirrels and other infected mammals. Animal species susceptible to monkeypox virus may include nonhuman primates, lagomorphs (rabbits), and some rodents. Predominant person-to-person transmission and prolonged chains of transmission were suspected in 1996 when 71 cases emerged in Katako-Kombe Health Zone, Kasai-Oriental, and Democratic Republic of the Congo, and again in 2003 in the Likouala region of Republic of the Congo.

There are 2 clades of monkeypox, the more infectious Congo Basin clade with a mortality rate of around 10% and the less infectious West African clade with a mortality rate of around 3%.

The most severe disease manifestations in prior African outbreaks were observed in children younger than 5 years of age.

In order to sustain the disease in the human population, it is believed that repeated animal reintroduction of monkeypox virus is needed.

In the United States, cases have primarily been limited to laboratory workers, pet shop workers, and veterinarians. There were 2 US cases in 2021 (July and November), both from travelers returning from Nigeria.

The first documented outbreak of monkeypox in the Western Hemisphere was attributed to a shipment of small mammals from Ghana to the United States in 2003. An infected Gambian giant rat from this shipment infected prairie dogs, which in turn transmitted the disease to humans. The prairie dogs were sold by a Milwaukee animal distributor to 2 pet shops in the Milwaukee area and during a pet "swap meet" (pets for sale or exchange) in northern Wisconsin. Patients from this outbreak reported direct or close contact with prairie dogs, most of which were sick. Illness in the prairie dogs was frequently reported as beginning with a blepharoconjunctivitis that was followed by the appearance of nodular lesions in some cases. Some prairie dogs died from the illness while others reportedly recovered.

Mortality rates differ based on the strain of monkeypox involved. The Central Africa (Congo Basin) clade is both more contagious and more severe with a reported mortality rate of around 10.6%. The West African clade is thought to be less severe with a mortality rate of about 3.6%. In the United States, there have been no fatalities.


B04 – Monkeypox

359814004 – Monkeypox

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Last Reviewed:05/29/2022
Last Updated:05/31/2022
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Monkeypox in Adult
Monkeypox : Chills, Fever, Headache, Central Africa, Lymphadenopathy, Myalgia, Umbilicated vesicles
Clinical image of Monkeypox
Copyright © 2022 VisualDx®. All rights reserved.