Monkeypox: For health professionals

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An unusually large number of cases of monkeypox have been reported from several non-endemic countries, including Canada. This is a departure from the usual epidemiology where sporadic cases used to occur in relation with travel to endemic countries in West or Central Africa. There are also sustained chains of transmission in some of the affected countries, likely through direct and often intimate contact with an infected person.

The situation is evolving, and this page will be updated as information becomes available.

What health professionals need to know about monkeypox

Monkeypox is a viral zoonotic infectious disease caused by an Orthopoxvirus. Person-to-person transmission can occur through direct contact with an infected person or shared contaminated objects. The possibility and extent of respiratory transmission is unclear at this time.

Historically, monkeypox has presented with a characteristic rash, which could be preceded by systemic manifestations such as fever. Lymphadenopathy is a feature that helps to differentiate monkeypox from other diseases with a similar rash (such as chickenpox).

Presentation of cases during the current outbreak has not always been typical. Please refer to What's unique to the 2022 multi-country outbreak section for additional details.

Management is mainly focused on supportive care, as there is limited data on the clinical effectiveness of specific treatments for monkeypox infections in humans. Some existing treatments and vaccines for smallpox may have a role to play in monkeypox management.

Agent of disease

The monkeypox virus is part of the Poxviridae family, which includes smallpox, vaccinia, cowpox, orf virus, and molluscum contagiosum. Specifically, it is a member of the Orthopoxvirus genus, which also includes smallpox, vaccinia, and cowpox.

There are two known virus subtypes of monkeypox (called clades):

  1. West African clade
  2. Congo Basin clade

The West African subtype has been implicated in the 2022 outbreak and compared to the Congo Basin clade, is associated with a relatively less severe infection.

Transmission

Monkeypox is typically characterized as a zoonotic infection for which the main reservoirs are unknown but are thought to be rodents such as dormice, striped mice, Gambian rats, and African rope squirrels. Humans and non-human primates are incidental hosts.

Infection is thought to occur when the virus enters the body through skin, the respiratory tract, or mucous membranes.

Historically, explosive and sustained outbreaks with very large numbers of affected persons have not been reported. However, human-to-human transmission does occur, sometimes leading to outbreaks in endemic areas.

Monkeypox can affect individuals of all ages. However, persons with a history of smallpox vaccination may have a protective advantage that may be more significant in those with more recent vaccination. Even though routine vaccination for smallpox in Canada generally stopped in 1972, other individuals and groups such as healthcare workers, armed forces personnel, and migrants may have been vaccinated after 1972. It is unknown if this vaccination program is still protective.

Animal-to-human

Person-to-person

Fomites

Clinical manifestations

The incubation period is usually from 6 to 13 days but can range from 5 to 21 days.

Monkeypox illness is usually self-resolving within a period of 2 to 4 weeks. However, severe cases can occur and may be fatal. Case fatality rate (CFR) depends on viral clade, host factors, and structural factors (such as availability of health care and reporting rates). The Congo Basin clade has a CFR of around 10%, while the West African clade, when occurring in endemic areas, has historically had a CFR of approximately 1 to 3%. When relatively small outbreaks of the West African clade have occurred in non-endemic countries, the CFR has been lower (for instance, during the 2003 US outbreak, there were no recorded fatalities).

The extent to which asymptomatic infection may occur is unknown. At this time, it is not known with certainty if a person can transmit the infection before they develop a fever or rash. However, it is believed that contagiousness may begin with the onset of symptoms. Individuals remain contagious until the scabs have fallen off on their own and the lesions are epithelialized.

Monkeypox signs and symptoms have been classically described in two stages:

  1. invasion (prodromal)
  2. skin eruption

Invasion stage

This first stage can last from 0 to 5 days. Signs and symptoms may include:

Skin eruption stage

The skin eruption generally appears 1 to 3 days after the onset of fever and lasts for 2 to 4 weeks. The rash is more prominent on the face or extremities as opposed to the trunk. However, it can affect other parts of the body, such as the hands (including the palms), feet (including the soles), mouth, genitals and perianal area.

As the illness progresses, the rash changes from flat lesions (macules) to raised lesions (papules) to vesicles and then pustules (see Figure 1). At the latest stage, they will form ulcers that eventually scab over. Monkeypox lesions in the same body area tend to evolve synchronously. However, individuals who have received prior smallpox vaccination may have an atypical or asynchronous rash. Figure 2 shows photographs of rash progression.

Figure 1. Clinical photograph of a monkeypox rash (pustular phase)
Figure 1. Clinical photograph of a monkeypox rash (pustular phase)

Reproduced with permission from Canadian Medical Association Journal.

Figure 1: Text description

This photograph depicts the hand of a child with monkeypox skin lesions. There are two round, well-defined, pustular lesions (lesions filled with pus). They are surrounded by red skin and located at the proximal end of the third digit (laterally and dorsally). The photograph includes a magnification of the lesions in the bottom right corner.

Figure 2. Series of six photographs that show the different stages of a monkeypox skin lesion
Figure 2. Series of six photographs that show the different stages of a monkeypox skin lesion

Reproduced with permission from United Kingdom Health Security Agency

Figure 2: Text description

This figure depicts a series of six photographs which illustrate the changes that occur to a monkeypox lesion throughout the progression of the disease. The images are arranged such that there are three photographs at the top and three at the bottom. The progression of the rash can be followed by looking at the photographs in order from the top left corner to the bottom right corner, moving from left to right. Each photograph focuses on a single lesion and does not allow for identification of the lesion's location on the body.

  • photograph in the top left corner: the photograph depicts a small and rounded vesicle (lesion filled with clear fluid). The skin surrounding the vesicle is reddened.
  • photograph in the top center: a pustule (lesion filled with pus) with an erythematous base is presented.
  • photograph in the top right corner: the photograph depicts an umbilicated pustule (pus filled lesion with umbilication resembling a dot on top).
  • photograph in the bottom left corner: the photograph depicts an ulcerated lesion (an open lesion with raised edges).
  • photograph in the bottom center: the photograph depicts an ulcerated lesion that has begun to crust over.
  • photograph in the bottom right corner: the photograph depicts a lesion that has been scabbed over.

In rare cases, the virus can cause complications such as:

What's unique to the 2022 multi-country outbreak

During the multi-country 2022 outbreak, not all cases are presenting in the typical fashion described above. Some individuals may initially present with exclusively oral, genital or perianal lesions, which may or may not be accompanied by symptoms of proctitis. Systemic symptoms characteristic of the prodromal stage could occur prior to or after the appearance of lesions. Some, but not all, may develop a more generalized rash, which may evolve asynchronously.

This content will be updated as new evidence becomes available about the clinical manifestations seen in this outbreak.

Diagnosis

To confirm the diagnosis of a monkeypox virus infection, one or more of the following diagnostic markers must be positive:

Consult your public health laboratory before sending specimens to receive proper instructions on specimen handling and transport.

Wear the adequate personal protective equipment when evaluating and sampling the patient.

The best specimens for PCR and isolation are skin lesion material, including:

Skin lesion material should be placed in an empty, sterile container for transport.

Although the preferred transport container for a monkeypox virus specimen is an empty, sterile container, formalin-fixed tissues and paraffin-embedded tissues can be sent for PCR, but not for viral culture.

Currently, serology is not ideal as there is significant cross reactivity with other Orthopoxviruses and previously smallpox vaccinated individuals.

Contact the National Microbiology Laboratory (NML) at nml.sp-lnm.asp@phac-aspc.gc.ca if you are unable to collect lesion swabs to discuss other possible viable sample types. You can also contact your local public health laboratory to inquire about other appropriate specimen types.

Given the evolving situation of the multi-country 2022 outbreak, the NML is relaxing the requirement to demonstrate travel to monkeypox virus endemic areas or contact to travellers or animals from these areas.

Test requisitions forms:

Differential diagnosis

Chickenpox (and others – refer to lists below) should be considered in the differential diagnosis. The main distinguishing feature of monkeypox is the presence of marked lymphadenopathy. Chickenpox tends to favour a truncal distribution while monkeypox is usually more predominant on the face or extremities. While chickenpox presents with lesions of different stages in close proximity, monkeypox lesions tend to have a similar size and stage of development on a single site of the body. Refer to the What's unique to the 2022 multi-country outbreak section above for more information.

Smallpox presentation can be similar to monkeypox presentation, but since its global eradication in 1980, it is not considered in the differential diagnosis unless there has been a serious laboratory breach.

Other rashes to be considered in the differential diagnosis can include:

In the case of ulcerative or crusting lesions consider the following:

Less common diseases to consider include other poxvirus infections, such as orf.

Management and treatment

Supportive care is a central part of monkeypox management as there is limited data on the clinical effectiveness of specific treatments for monkeypox infections in humans. Consult an infectious disease physician to discuss therapeutic options for suspected or confirmed cases.

Some existing treatments for smallpox, such as TPOXX® (tecovirimat monohydrate capsules) may have a role to play in select instances. TPOXX® is an oral antiviral agent that is indicated for the treatment of human smallpox disease in adults and pediatric patients weighing at least 13 kg. It does not have an approved Health Canada indication for monkeypox or other Orthopoxviruses.

IMVAMUNE® is a licensed 3rd generation smallpox vaccine indicated for active immunization against smallpox, monkeypox and related Orthopoxvirus infection and disease in adults 18 years of age and older determined to be at high risk for exposure.

The Public Health Agency of Canada (PHAC) has been working closely with the provinces and territories, international partners, and infectious disease experts to discuss the circumstances under which this vaccine should be used. PHAC is identifying what is known and unknown in this new and emerging situation, and is working with these partners to identify how to best utilize this vaccine in the Canadian context. The vaccine approach is evolving as we learn more about the possible modes of transmission of the virus, how the disease manifests in different populations, and as the public health case management response rolls out.

The National Advisory Committee on Immunization (NACI) has issued Interim guidance on the use of Imvamune® in the context of monkeypox outbreaks in Canada. A Summary of NACI rapid response of June 10, 2022 is also available.

The PHAC National Emergency Strategic Stockpile (NESS) maintains a supply of vaccines and therapeutics, and continues to work with provinces and territories to support collective preparedness and, as required, outbreak management. Health care facilities and local or regional health departments should direct requests for these vaccines and therapeutics to their respective provincial or territorial Ministry of Health (MOH).

For more information on these medical countermeasures, refer to the Product Monographs available on Health Canada's Drug Product Database.

Infection prevention and control

As the modes of transmission in the current outbreak are not well understood, airborne, droplet and contact precautions are recommended in a healthcare setting.

For guidance on infection prevention and control for monkeypox, refer to the Interim guidance on infection prevention and control for suspect, probable or confirmed monkeypox within Healthcare settings – 27 May 2022 web page.

Surveillance

If you suspect a case of monkeypox, contact your local public health authority.

PHAC is working with provincial and territorial public health partners to investigate cases of monkeypox in Canada. For epidemiological updates, and to learn more about how Canada is monitoring monkeypox, refer to the Monkeypox: Outbreak updates web page.

Additional resources

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