Canadian Medical Association

Outbreaks of monkeypox infection have been reported in atypical areas and in people without travel links to endemic regions. While epidemiologic investigations are initiated and we learn more about these unusual clusters of infection, here’s what we know about monkeypox so far.

1. What is monkeypox?

Monkeypox virus, now known as mpox, is a member of the Orthopoxvirus genus in the family Poxviridae, which includes variola virus (which causes smallpox) and vaccinia virus (which is used in one of the smallpox vaccines). Monkeypox is a zoonotic infection, but its wild animal reservoir is unknown.

There are two genetically distinct clades of monkeypox that vary epidemiologically and clinically. The Congo Basin strain is estimated to have a fatality rate of 10%. The West African strain (confirmed in the UK cases) has a fatality rate of about 1%.

2. Where did monkeypox come from?

Monkeypox was first identified in an outbreak of research monkeys (hence the name). The first human cases were reported in 1970 in the Democratic Republic of Congo, and since then, isolated outbreaks have occurred throughout Central and West Africa. Few cases have been reported elsewhere; many of these have been associated with travel to Africa.

In 2003, dozens of suspected cases of monkeypox in the United States were reported to the US Centers for Disease Control and Prevention from six different states. Investigations revealed that all the cases had contact with newly acquired pet prairie dogs that had been imported from Africa. This outbreak was contained and no human-to-human spread of monkeypox was identified.

3. How does monkeypox spread?

Animal-to-human spread of monkeypox (i.e., spillover) occurs through a bite, scratch or contact with animal fluids, such as in the preparation of wild game. Human-to-human spread occurs through contact with bodily fluids, including pus from lesions and respiratory droplets. A patient is considered contagious from the onset of symptoms until lesions have healed, which may take one month or more.

It's not clear if monkeypox is transmitted by sexual intercourse. It’s possible prolonged close contact, exposure to lesion material, or contact with contaminated clothing or bedding is a contributing factor, regardless of sexual orientation.

4. What are the clinical features of disease due to monkeypox infection?

Monkeypox has a rather long incubation period, ranging from five to 21 days between infection and onset of symptoms. Early symptoms are nonspecific and include fever, fatigue, headache and myalgia. Monkeypox infection also causes swelling of lymph nodes — a notable distinction from smallpox, though less clinically useful now than in the past, since smallpox has been eradicated.

This prodrome is followed by a progressive rash characterized by deep-seated and well-circumscribed lesions. The first lesions may be mucosal, commonly occurring on the tongue and in the mouth; these are followed by a macular rash on the face before spreading throughout the body. Over the course of a few weeks, lesions progress from macules to raised papules. They become vesicular then pustular, and they ultimately crust and scab over before falling off.

Some of the cases described so far in 2022 have involved localized rashes in the genital and perianal region, causing them to be confused with common sexually transmitted infections. A high index of suspicion is warranted for anyone with a characteristic rash plus either a travel history to an endemic area or close contact with someone with a rash that is similar in appearance.

All suspected cases should be reported to infection control personnel, and health care workers caring for patients should follow standard contact and droplet precautions.

Guidance on infection prevention and control for monkeypox

The Public Health Agency of Canada recently issued interim guidance on infection prevention and control for monkeypox within health care settings, recommending that airborne, droplet and contact precautions be used for all suspect, probable and confirmed cases of monkeypox. Learn more.

5. Is there a treatment or a vaccine for monkeypox?

There is no proven treatment for monkeypox infection, although a few antivirals have been tested. Cidofovir and brincidofovir have shown activity against poxviruses in in vitro and animal studies. Another drug, tecovirimat, is approved by Health Canada and the US Food and Drug Administration (FDA) for treatment of smallpox.

A new vaccine called Jynneos was granted FDA approval in 2019 for the prevention of both smallpox and monkeypox, although its real-world effectiveness is unknown. It is also thought that traditional smallpox vaccination with the closely related vaccinia virus is likely to provide some protection. Global smallpox vaccination programs ended in the 1970s; since then, there has been only rare, targeted vaccination of select individuals, such as military personnel and researchers working with pox viruses. We learned from the 2003 outbreak in the US that previous immunization with the smallpox vaccine was not completely protective, so it’s not clear whether people vaccinated 50 or more years ago would have sufficient immunity.

While these monkeypox outbreaks do not pose a great threat to the general public, physicians should be on alert for its characteristic lesions, even in unusual body areas such as the genitals.

Original article published on EBM Focus. Written by:

  • Heather D. Marshall, PhD, Public Health Content Manager at DynaMed; and
  • Vito Iacoviello, MD, Deputy Editor for Infectious Disease, Allergy, and Immunology at DynaMed.

CMA members have access to DynaMed, a point-of-care reference tool valued at US$399 per year, as part of their membership.

Do you have a question on COVID-19 or another clinical topic? Contact the Ask a Librarian team to request a literature search.

Back to top