Mpox is a viral infection, caused by a virus of the Orthopoxvirus genus. There are two circulating clades of the Mpox virus: clade I (formerly named the Congo Basin Clade) and clade II (formerly named the West African Clade), which historically has been associated with less severe disease and lower-case fatality compared to Clade I. Clade II has been responsible for several recent outbreaks including one in 2017-2018 in Nigeria, and most recently in 2022 with cases in Western Europe, North America and Australasia.
The first Mpox case in Canada was reported on May 19, 2022, in Montreal and British Columbia’s first case was confirmed on June 6, 2022. The outbreak was declared over on January 9, 2023. Genomic studies linked most of the cases from the cases in the 2022 outbreak in Europe and America to clade II lineage B.1.
We anticipate we will continue to see sporadic
cases associated with travel related introductions from elsewhere in Canada and globally. Therefore, it is necessary to remain vigilant for symptoms of Mpox, and eligible individuals should be offered and complete their vaccination series. Individuals with a single dose should be offered a second dose to complete the series, the minimum recommended interval between doses in 28 days. There is no maximum interval.
Currently there is an outbreak of clade I in the Democratic Republic of Congo (DRC), which has seen cases extend to neighbouring countries, resulting in a declaration of a public health emergency of international concern (PHEIC) by the World Health Organization (WHO) on August 14, 2024. Clade I has two subclades, Ia and Ib.
Clade Ia is endemic in the DRC. Mpox cases of this clade have mostly affected children, are associated with an aggregated case fatality rate of 3.6% (WHO 2024 data), and the spread is likely sustained through multiple modes of transmission including person-to-person transmission following zoonotic introduction in a community. The risk in Canada to the public of clade Ia Mpox remains very low.
Clade Ib is a new subclade that emerged in the DRC and is transmitting between people, most likely via close-intimate and sexual contact. One case of this subclade also been reported in Sweden and Thailand each as of August 26, 2024. The risk in Canada to the public of clade Ib Mpox is low. B.C. and Canada continue to monitor the Mpox situation and will update the risk assessment as more information is known about clade Ib.
Among the Mpox cases in Canada, a high proportion has been in people who self-identify as gay, bisexual, and other men who have sex with men (gbMSM). Though the reported cases thus far have been primarily among gbMSM, it is important to note that anyone can become exposed and infected.
Mpox is not known to be sexually transmitted, but it can occur through close direct contact. Anyone with close and prolonged contact with a case of Mpox is at risk of having the infection.
Stigmatizing any group will hinder appropriate infection prevention and control efforts and will be detrimental to the identification and management of additional cases. The recent cases among gbMSM are likely due in part to shared social networks, as well as large events that may have facilitated transmission.
In B.C., vaccination is available to close contacts and those at the highest risk of infection. Public health will follow up with individuals who may have been exposed to Mpox or who are identified as cases.
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Incubation: 5 to 21 days, usually 7 to 14 days
Image credit: United Kingdom
Clinical presentation resembles smallpox but is less severe. Symptoms can vary depending on different factors, including exposure characteristics, age, presence of conditions that alter immune response, previous immunity for smallpox and viral strain.
Mpox infection generally has two clinical phases:
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A prodromal illness that lasts between 1 to 5 days characterized by fever, intense headache, lymphadenophathy, back pain, myalgia, fatigue. Other symptoms have been also described, such as sore throat, cough and less frequently, vomiting or diarrhea. In some cases, no prodromal symptoms were reported, or these symptoms occurred after the beginning of the rash.
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A skin rash that begins 1-5 days after fever. The rash evolves from macules, papules, vesicles then pustules, before crusting, which then scale off. Lesions are frequently painful and can be pruritic. Lesions of different clinical stages can be present at the same moment.
The number of lesions and affected regions can vary. Those who are vaccinated tend to have fewer lesions and a milder illness. Lesions can be found on all parts of the body, including palmar and plantar areas. Localized pain or swelling in regions such as the throat or rectum without visible sores can also occur. Asymptomatic or Subclinical infection can occur.
In patients with potential exposure in Canada, lesions frequently begin and affect the genital, anal and oral areas. Some cases developed proctitis (rectal pain, bloody stools, diarrhea). Facial lesions can potentially lead to ocular involvement, affecting the conjunctivae and cornea. Clinical presentation for those in the outbreak areas of Africa may differ, so a high index of suspicion should remain for anybody reporting skin lesions returning from outbreak areas.
Symptoms last 2 to 4 weeks.
Special populations such as children, pregnant people and some immunocompromised individuals are considered at higher risk for severe disease. Recent cases in Canada and western countries have been described as mild. Hospitalizations are uncommon but may be needed for pain control or management of secondary complications. Deaths are rare in developed countries.
Long-term skin effects, such as prolonged ulcer healing and scarring, have been described in the literature. Complications can include secondary infections (for example, cellulitis), and less frequently pneumonia, sepsis, encephalitis and keratitis leading to vision loss.
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The period of communicability is the time during which an infectious agent may spread directly or indirectly from an infected person to another person; it is also known as the 'infectious period'. Emerging evidence suggests that some Mpox cases can transmit the virus up to 4 days prior to symptom onset and remain infectious until lesions have fully resolved, (i.e., crusts fall off and new skin is forming underneath).
Most historical transmissions occurred through close contact with infected animals (bite, scratch, or ingesting meat). This is likely the origin of the current Clade I outbreak in Central and Eastern Africa, with subsequent household and close-contact transmission, especially amongst children, The global outbreak of Clade II, however, is facilitated by human-to-human transmission typically during intimate contact. The new clade Ib is spreading through sexual contact and household contacts. Most cases in the 2022 BC outbreak were exposed during close, intimate contact during sex.
Human-to-human transmission occurs most efficiently via:
- Direct skin-to-skin contact, especially with cutaneous lesions.
- Direct contact with affected mucosal surfaces or secretions.
Mpox has been detected in many body sites, including semen. However, the significance of this finding on the potential for sexual transmission through semen is not yet known. Transmissions in the context of sexual activity are likely related to close contact as described above.
Mpox can also be transmitted through fomites, i.e., contaminated material such as linens or clothing, and through respiratory droplets from prolonged face-to-face contact, but less efficiently than direct contact.
Mpox virus can cross the placental barrier. No case of vertical transmission has been reported in non-endemic countries. However, a case of fetal infection with pathological signs of Mpox has been described from an endemic country, indicating the potential for vertical transmission.
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Mpox diagnosis is available in B.C. by PCR (nucleic acid) testing (detecting the presence of Mpox virus DNA in patient samples). Positive samples are sequenced to determine the strain type (Clade). For guidance on sample collection and transport, please contact your local microbiology laboratory. Mpox is a notifiable condition in B.C., and across Canada.
Refer to the Mpox Testing Guidelines for Primary Care in British Columbia:
Mpox Testing Guidelines for Primary Care in British Columbia (PDF)
Suspected cases should be instructed to limit their contact until testing results are obtained and practice frequent hand and respiratory hygiene. Lesions should be covered whenever possible, and contaminated objects should be manipulated by the case only.
See also Immunization.
Refer to the Provincial Infection Control Network's infection prevention and control guidance for Mpox:B.C.'s interim infection prevention and control guidance for Mpox in health care settings
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If a patient suspected or confirmed to have Mpox requires transportation, the patient must be provided with a medical mask and lesions must be covered (e.g., patient gown, sheet, or dry dressing). The receiving department/facility and transporting personnel should be informed of the need for airborne, droplet and contact precautions.
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Last updated: August 27, 2024
