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.
Mpox cases were first identified in BC in 2022, with levels remaining relatively low in recent years. Please see the
STBBI & TB report for current numbers
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 subclade that emerged in the DRC and is transmitting between people, most likely via close-intimate and sexual contact. More than 300 cases of have been reported to date; however, there have been no deaths. The risk in Canada to the general public of clade Ib Mpox infection is low. BC and Canada continue to monitor the Mpox situation.
Among the Mpox cases in Canada, most have been among gay and bisexual men, or other men who have sex with men. However, cases have occurred in other groups. Mpox is primarily spread through sexual contact, but anyone with close and prolonged contact with a case of Mpox is at risk of having the infection.
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 four days prior to symptom onset and remain infectious until lesions have fully resolved, (i.e., crusts fall off and new skin is forming underneath).
Mpox is primarily spread through sexual contact, however, anyone with close and prolonged contact with a case of Mpox is at risk of having the infection.
Person-to-person
Transmission can occur through direct contact with:
- skin lesions or scabs
- body fluids (such as blood, saliva and semen)
- mucosal surfaces (such as eyes, mouth, throat, genitalia and anorectal area)
- from an infected pregnant person to the fetus
While transmission through the air can happen, available data suggests this risk is minimal.
Fomites
Transmission can also occur through unprotected contact between skin and objects such as:
- surfaces
- materials (clothing or linens and towels)
- objects (needles, razors, sex toys, toothbrushes, utensils) that have come into contact with an infected person or animal
In BC, 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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Mpox diagnosis is available in BC 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 BC, and across Canada.
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 the Immunizations tab at the top of the page.
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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