Factsheet for health professionals on mpox (monkeypox)

Last reviewed/updated on: 1 June 2023

Disclaimer: The information contained in this factsheet is intended for the purpose of general information and should not substitute individual expert advice or judgement of healthcare professionals.

The pathogen

The monkeypox virus (MPXV) is an enveloped virus with a double‐stranded DNA genome that belongs to the Orthopoxvirus genus of the Poxviridae family. The Orthopoxvirus genus also includes vaccinia virus, cowpox virus, variola virus, and several other animal pathogen poxviruses [6]. There are two genetically distinct clades described for MPXV: Clade I, formerly called the Congo Basin (Central African) clade, and Clade II, formerly called the West African clade, with sub-clades IIa and IIb [7,8]. Genetic differences between the viral genomes of the two clades might explain differences in viral clearance and pathogenesis [7,9,10]. Clade I has been associated with more severe disease and higher mortality [2,4,11,12].

Poxviruses show extraordinary resistance to drying [13], and a higher temperature and pH tolerance compared to other enveloped viruses. These characteristics strongly impact their environmental persistence. Viruses of the Orthopoxvirus genus are known to have a long-lasting stability in the environment [14], and viable MPXV can be detected on household surfaces at least 15 days after contamination of the surfaces [15]. Vaccinia virus (the virus contained in the smallpox vaccine) is rapidly inactivated in sewage [16]. Despite these characteristics, poxviruses are sensitive to common disinfectants. However, they can be less sensitive to organic disinfectants compared to other enveloped viruses.

MPXV is considered an ‘agent with high threat for deliberate release’ using the matrix developed by the European Commission task force on Bioterrorism (BICHAT) [17].

Clinical features and sequelae

Based on studies in Central and West Africa, the incubation period for mpox is described as usually lasting from 6–13 days, but may also range from 5–21 days [18]. Human mpox often begins with a combination of the following symptoms: fever, headache, chills, exhaustion, asthenia, lymph node swelling (lymphadenopathy), back pain, and muscle aches [12,19]. In cases in endemic areas (Africa), within three days after the onset of these prodromal symptoms, a centrifugal maculopapular rash starts from the site of the primary infection. It rapidly spreads to other parts of the body and progresses to develop vesicles. Palms and soles are involved in cases of the disseminated rash, which are characteristic of the disease. The number of lesions may range from a few to thousands [20], and an increasing number of lesions is correlated with increased disease severity.

The majority of human mpox cases experience mild to moderate symptoms typically lasting from two to four weeks, followed by complete recovery with supportive care [18]. The disease severity may vary depending on the transmission route, host susceptibility, and the quantity of virus inoculated [11], with invasive modes of exposure causing more severe disease while having a shorter incubation period [21].

Complications in endemic countries include encephalitis, secondary bacterial skin infections, dehydration, conjunctivitis, keratitis, and pneumonia. The case-fatality ratio (CFR) of mpox ranges from 0–11% in outbreaks in endemic areas, with mortality mostly affecting young children [18]. People living in or near tropical forested areas may have indirect or low-level exposure to infected animals, possibly leading to subclinical (asymptomatic) infection [18,22]. In endemic areas, immunocompromised individuals were reported being particularly at risk of severe disease [23]. In an outbreak in Nigeria in 2017, patients with concurrent HIV infection had more severe disease with more skin lesions and associated genital ulcers compared to HIV-negative individuals. No deaths were reported among HIV-positive patients [24]. In Nigeria, from September 2017 to June 2022, 257 confirmed cases were identified, including nine deaths (CFR=3.5%), at least five of which were immunosuppressed [25,26]. Major disease sequelae are usually disfiguring scars and permanent corneal lesions [4].

Clinical features and sequelae related to the worldwide mpox outbreak in 2022

Studies on the multi-country mpox outbreak which started in May 2022 showed an incubation period of 7–8 days (interquartile range (IQR) 5–10) [27-30]. Shorter incubation periods of 2–4 days were also observed, possibly due to direct viral inoculation via sexual transmission [29,31-33]. Data from a contact tracing study in the United Kingdom (UK) which was used to estimate the distribution of incubation periods, showed that 95% of people with potential infection would manifest symptoms within a period of 16–23 days [34]. 

Additionally, a clinical presentation of symptoms which is somewhat different compared with those previously reported in endemic areas, has also arisen. In the 2022 outbreak, systemic prodromal symptoms started after the rash in up to half of the cases, while they were completely absent in several cases. Systemic prodromal symptoms included fever, fatigue, myalgia, and headache [27,33,35,36].

In the 2022 outbreak, most patients presented with fewer than 20 lesions. Cases with more than a hundred lesions were rare [33]. Lesions on the oral mucosa (enanthem) or ophthalmic mucosa were also present. Clinical manifestations in travel-related cases previously detected in western countries have usually been mild, sometimes with very few lesions [37]. A majority of the cases presented with lesions in the anogenital and perioral regions, as well as lymphadenopathy in the catchment area of the lesions [33,38,39]. However, in some cases, the number of lesions were quite limited, including cases of single cutaneous or mucosal anogenital or oral lesions [29]. Patients may also have presented with proctitis. Oropharyngeal involvement also occurred, which included oral lesions, tonsillitis and peritonsillar abscess causing pain and difficulty in swallowing, and epiglottitis affecting breathing [33,36].

The lesions progressed from the stage of macules to papules, vesicles, pseudo-pustules containing solid debris, crusts, and finally scabs, before falling off within 7–14 days [40]. In the 2022 outbreak, lesions were found to present at different stages in the same patient, although lesions in the same area typically appeared and evolved simultaneously. Not all lesions progressed from one phase to the next in order [33]. The lesions were deep-seated, may have been centrally depressed (umbilicated), and could have been accompanied by pruritus and/or pain. Scratching may have facilitated secondary bacterial infections.

A minority of cases (1–13%) were hospitalised for isolation, pain management, or for complications such as secondary skin infections, abscesses, and difficulty in swallowing [33,36,39,41]. Less severe but more common complications included rectal pain, swelling of the penis, and secondary bacterial infections [33]. Serious complications were rare and included epiglottitis, myocarditis, and encephalitis [29]. Sporadic fatal cases were reported [42] and the overall CFR in the 2022 outbreak was less than 0.1% [33].

In the 2022 outbreak, people living with HIV/AIDS (PLWHA) accounted for 38–50% of mpox cases worldwide [33]. Several studies have shown no difference in clinical presentation between HIV-positive and HIV-negative mpox cases in this outbreak, but these patients were mostly PLWHA with viral suppression and high CD4 cell counts [27,33,43]. However, in PLWHA with CD4 cell counts of <100 cells per mm³, severe complications were more common than in those with CD4 cell counts between 300 and 350 cells per mm³, including necrotising skin lesions, lung involvement and secondary infections with sepsis [41]. A 15% mortality rate was described among individuals with advanced HIV-related disease characterised by CD4 cell counts below 200 cells per mm3 [41]. An immune reconstitution inflammatory syndrome (IRIS) to mpox was suspected in 21 (25%) out of 85 people who were initiated or re-initiated on antiretroviral therapy (ART), of whom 57% died.

Epidemiology

Mpox is regarded as the most significant orthopoxvirus infection affecting humans since the eradication of smallpox [44]. MPXV was first isolated in 1958 from pox lesions during an outbreak of vesicular disease among captive cynomolgus macaques (Macaca fascicularis) imported from Singapore into Denmark for polio-vaccine-related research [23].

Although the previous name of the disease (i.e. monkeypox) suggested that monkeys are the primary host, the specific animal reservoir of MPXV remains unknown [23]. In nature, many animal species were found to be infected with MPXV, including rope and tree species of squirrels, Gambian pouched rats (Cricetomys gambianus), striped mice, dormice, and primates [1]. Some evidence suggests that native African rodents such as Gambian pouched rats and rope squirrels might be a natural reservoir of the virus [5,45].

The first detection of MPXV in a human was in 1970 in the equatorial region of the Democratic Republic of the Congo (DRC), nine months after the eradication of smallpox in that country [46]. Subsequently, sporadic cases were reported from the rainforest areas of Central and West Africa. Large outbreaks were also identified, mainly in the DRC, where the disease is currently considered endemic [46,47].

Following the declaration of the eradication of smallpox in 1980 by the World Health Assembly, the World Health Organization (WHO) sponsored enhanced mpox surveillance efforts in the central regions of the DRC, for which some limited animal and human ecological studies were undertaken [4]. This led to a major increase in the reported incidence of mpox.

Human mpox was reported outside of Africa for the first time in 2003, when an mpox outbreak occurred in the United States [48,49]. A total of 81 human cases of mpox in several states were reported among people who had close contacts with pet prairie dogs; the prairie dogs were housed with MPXV-infected rodents imported from Ghana. No human-to-human transmission was identified, and no deaths among humans were reported. Following this outbreak, there was no evidence that the virus became enzootic in wildlife in the United States.

While the majority of documented cases of mpox in Africa have occurred in the DRC, the number of cases in other West and Central African countries have also increased in the last decade [1]. This increase may be partly attributable to decreasing herd immunity in the populations following the cessation of the smallpox vaccination program in the early 1980s. Other explanatory factors may have been changes in the virus itself and modifications to the ecosystems that may have caused the population density of the natural reservoirs to rise [46] and led to more frequent human-wildlife interactions. Since 2016, confirmed cases of mpox have been reported from the following African countries: Cameroon (Clade II) [50], Central African Republic (Clade I), the DRC (Clade I), Liberia (Clade II), Nigeria (Clade II), the Republic of the Congo (Clade I), and Sierra Leone (Clade II) [1,51-53]. Sporadic imported cases of mpox were reported in countries outside of Africa as well: the UK [54-56], Israel [57], and Singapore [58,59]. All these cases had travelled from Nigeria. In 2021, the UK reported one family cluster: the primary case was exposed in Nigeria and subsequently infected his family members back in the UK [60,61]. 

In May 2022, a multi-country outbreak of mpox was declared, with all EU/EEA countries (except for Liechtenstein) eventually reporting locally acquired cases. The outbreak was driven by human-to-human MPXV transmission via close contact with infected individuals. The majority of cases were men-who-have-sex-with-men (MSM). As of 3 May 2023, EU/EEA countries had reported a total of 21 223 confirmed mpox cases [62]. More information about the 2022 outbreak for the EU/EEA is available on the ECDC website, and for a worldwide overview on the WHO website.

Transmission

MPXV is transmitted to humans through close contact with an infected animal or human, or contact with materials contaminated with the virus [1,63]. The virus enters the body through broken skin or the mucous membranes [63]. Human-to-human transmission of mpox occurs through: close contact with infectious materials from the skin or mucosal lesions of an infected person, respiratory droplets in prolonged face-to-face contact, and fomites [2,18,33,63]. Human-to-human transmission also occurs during sexual contact [64]. The risk of infection following sexual exposure is high – in a contact tracing study in connection with the 2022 outbreak, 67% of exposed sexual contacts were ‘definitely or possibly’ infected compared to only 14% of non-sexual contacts [65].

MPXV is more often detected from skin, anal and throat samples than from blood, urine, and semen [66]. Viral load in skin samples have been shown to be substantially higher compared to viral loads taken from other locations [33,67]. However, high viral loads have also been detected in anorectal samples, in particular, from patients with anorectal lesions [66]. Replication-competent MPXV has been isolated in samples from skin lesions and anorectum, and less frequently from the oropharynx [67].

Whether transmission of MPXV through genital secretions can occur is currently unclear.  Other (rare) transmission routes, such as mother-to-child transmission [68] or nosocomial infection [69,70] have also been documented. While transmission through substances of human origin (SoHO) has never been reported, transmission during pregnancy and through the bites or scratches of an ill animal suggest that this transmission mode is theoretically possible [21].

Emerging evidence indicates that infected people may transmit MPXV up to four days prior to symptom onset. This evidence comes from modelling studies, studies on linked transmission pairs with known exposure times [28,34], and a viral shedding study that found viral DNA four days before symptom onset [65]. A study conducted in the UK found that 53% of transmission occurred during the pre-symptomatic period [34].

The infectious period lasts until all skin lesions have scabbed over and re-epithelialisation has occurred [33]. The proportion of positive samples from cases has been seen to decrease substantially by around three weeks from symptom onset [66]. However, one study found that it takes around 40 days for 90% of the cases to have undetectable viral DNA in semen and skin lesions. This time was shorter for other types of lesions, although replication-competent MPXV was only detected up to three weeks after illness onset [67]. People with severe HIV infection have been shown to have a longer course of illness. Further studies are needed to determine whether this has an impact on the duration of infectivity [41].

Asymptomatic mpox infections have been reported as well. Studies have found that between 1.3% and 6.5% of infected people have never experienced symptoms [71-73]. The role of asymptomatic cases in transmission is currently not clear.

Diagnostics

Real-time polymerase chain reaction (real-time PCR) on skin lesion materials (e.g. swabs, exudate, or lesion crusts) is used to diagnose mpox. Several real-time PCR assays for the specific detection of MPXV, or for generic orthopoxvirus detection are available [74-79]. Mpox laboratory diagnostics are well established in several laboratories in Europe (see Emerging Viral Diseases-Expert Laboratory Network – EVD-LabNet [80]).  

Serological tests have limited value in mpox diagnostics due to immunological cross-reactivity between human-pathogenic orthopoxviruses [81], although they can be useful for excluding a recent or past orthopoxvirus infection. For contact investigations and population serosurveys, Immunoglobulin M (IgM) and Immunoglobulin G (IgG) detection by enzyme-linked immunosorbent assay (ELISA) or immunofluorescent antibody assay (IFA) is available in some laboratories.

Diagnostic procedures for MPXV and manipulation of specimens suspected to contain MPXV should be performed in biosafety level (BSL)-2 facilities as a minimum requirement [82,83]. MPXV is classified as a safety group 3 biological agent. Activities involving the handling of MPXV should, therefore, only be done in working areas corresponding to at least containment level three [83].

Case management and treatment

Newly identified cases of mpox should undergo a medical assessment for severity and risk factors (e.g. underlying conditions or medications affecting immune competence, untreated HIV infection, etc.). Those at increased risk of severe disease from mpox may require hospitalisation and/or treatment with antivirals. Population groups at increased risk for severe disease include infants and young children, pregnant women, the elderly, and severely immunocompromised persons.

Cases should be instructed to isolate until their rash heals completely, which indicates the end of infectiousness. Recommendations mainly include the following:

• Cases should remain in their own room, when at home, and use designated household items (clothes, bed linen, towels, eating utensils, plates, glasses, etc.), which should not be shared with other members of the household.
• They should avoid contact with immunocompromised persons and other persons at risk for severe disease (such as infants and pregnant women) until their rash heals completely.
• They should be monitored by public health authorities (e.g. via telephone calls or other means, according to national guidance).
• They can temporarily leave their home (e.g. for medical appointments and necessary outdoor exercise for the stability of their mental health), provided they wear a medical face mask, and their rash is covered (e.g. by wearing long sleeves and trousers).
• They should practise careful respiratory hygiene and wear a medical face mask when in contact with other people. In addition, mpox cases and their household contacts should practise careful hand hygiene at all times.
• They should abstain from sexual activity until their rash heals completely i.e. no new lesions appear, scabs have fallen off, and new skin has formed.  
• They should avoid contact with any mammalian animals (see also section on ‘Special considerations to mitigate the risk of animal-to-human and human-to-animal transmission’).

Treatment is primarily symptomatic and supportive (alleviation of fever, pruritus and pain, and hydration), including the prevention and treatment of secondary bacterial infections. Tecovirimat is the only antiviral drug with an indication for the treatment of orthopoxvirus infections, including mpox, with a market authorisation in the EU [84]. Brincidofovir and cidofovir are other antiviral drug options for severe mpox cases, but have significant side effects [85].

Public health control measures

Public health authorities can take several public health measures to mitigate transmission:

• Raise awareness by appropriately targeted communication aimed at those most at risk for transmission or severe disease, including the active involvement of key stakeholders at the community level.
• Facilitate the early diagnosis of cases through easy access to healthcare services with well-informed clinicians, accessible diagnostics, and management guidance.
• Facilitate the early detection of cases by contact tracing in outbreak settings [86].
• Facilitate the isolation of mpox cases.
• Implement partner notification and contact tracing, in line with national recommendations.
• Implement appropriate infection prevention and control measures in healthcare settings [87].
• Implement a national vaccination strategy against mpox.

Infection control, personal protection and prevention

Populations at increased risk of infection

Sexual contact seemed to be a particular risk factor driving the mpox outbreak in 2022. Cases were identified primarily, but not exclusively, among men who have sex with men (MSM). Particular sexual practices (e.g. having multiple and frequent anonymous sexual contacts, and receptive anal sex) may have contributed to putting people at higher risk of infection. People who closely interact with an infectious person, including healthcare workers, household members, sexual partners, and commercial sex workers are at greater risk of infection [27,64,88]. Occupational exposure and infection with orthopoxviruses have been occasionally reported among laboratory personnel handling virus-containing specimens [89].

Vaccine and vaccination strategies

Since 22 July 2022, the third-generation non-replicating smallpox vaccine Imvanex – Modified Vaccinia Ankara - Bavarian Nordic (MVA-BN) was authorised in the EU for protection against mpox in adults [90,91]. The vaccine had already been approved for active immunisation against smallpox in 2013 [90].

Imvanex is authorised to protect adults from mpox as well as disease caused by the vaccinia virus. These new indications were added to Imvanex's existing authorisation against smallpox, which has been in place in the EU since 2013. For protection against mpox, Imvanex is administered as a subcutaneous injection (0.5 ml), with a two-dose regimen. The second dose is given at least 28 days after the first as primary vaccination to individuals previously not vaccinated against smallpox, monkeypox or vaccinia viruses [92]. At the time of authorisation, data from human and animal studies suggested that a single dose of MVA-BN may offer fast protection against mpox, and that the second dose mainly serves to extend the durability of protection [90]. Similarly, it was indicated that a single booster vaccination dose (0.5 ml) may be considered for individuals previously vaccinated against smallpox, mpox or vaccinia viruses, although there are inadequate data to determine the appropriate timing of the booster doses [92]. The safety profile of MVA-BN is favourable, with mild to moderate side effects. Older generation smallpox vaccines have significant side effects and are not authorised by the European Medicines Agency (EMA).

MVA-BN is authorised for use against infection and disease caused by both smallpox and MPXV in the United States (Jynneos) [93] and Canada (Imvamune) [94] as well as other related orthopoxviruses (Canada only).

Considering the limited supplies of Imvanex in the EU/EEA in the summer of 2022, in August 2022 the Emergency Task Force (ETF) of EMA issued a recommendation to support vaccination strategies for antigen sparing (intradermal delivery of a fractional dose) [95]. The evidence reviewed at the time indicated that the lower intradermal dose of the vaccine (one-fifth of the subcutaneous dose) has a comparable humoral immunogenicity to the standard subcutaneous dose.

Robust data on the clinical efficacy of the third-generation vaccines against mpox are still lacking, but the first results of vaccine effectiveness studies are becoming available. The available evidence indicates that the MVA-BN vaccine provides protection against mpox. Infection can still appear after one vaccine dose, but the illness becomes less clinically severe, and hospitalisations are reduced.

Primary preventive (pre-exposure) vaccination (PPV) in the mpox outbreak of 2022

PPV refers to the vaccination of groups of individuals at high risk of exposure to MPXV. The level of risk of infection may differ between these groups, and is also linked to the specific epidemiological situation. Both aspects could be used by the countries for prioritisation purposes in case of limited supply of vaccines.

During the outbreak of 2022, EU/EEA countries were advised to prioritise PPV among individuals at substantially higher risk of exposure to MPXV, such as individuals identifying themselves as gay, bisexual, or other men or transgender people who have sex with men. This prioritisation was based on certain epidemiological or behavioural criteria (e.g. recent history of multiple sexual partners or plans to engage with multiple partners, attending sex-on-premises venues, or group sex or chemsex practices, use of or eligibility for pre-exposure prophylaxis for HIV, recent history of sexually transmitted bacterial infections, etc).

In addition, PPV was suggested for workers in sex-on-premises venues, if they were regularly exposed to items (i.e. bed linens) or surfaces likely to be contaminated with body fluids or skin cells, as well as other groups at higher risk, such as sex workers. PPV for others who believed they were also at risk, or who did not wish to declare which risk group they belonged to, could be considered on the basis of a case-by-case assessment.

PPV should be considered for healthcare workers at risk of occupational exposure, especially those at repeated risk of exposure, laboratory personnel (e.g. laboratory staff working with orthopoxviruses or in clinical laboratories performing diagnostic testing for MPXV), and outbreak response staff.

However, PPV should not be considered solely on the basis of higher risk of severe disease (e.g. children, pregnant women, and immunosuppressed individuals are considered as having a higher risk of severe disease) [90,96].

To ensure effective outreach, high vaccine acceptance and uptake among those most at risk of exposure, targeted health promotion interventions and community engagement is deemed necessary.

Post-exposure preventive vaccination (PEPV) in the mpox outbreak of 2022

PEPV refers to the immunisation against MPXV of close contacts of cases to prevent the onset of disease or mitigate the disease severity. This strategy depends on the possibility of identifying contacts of cases through contact tracing.

The priority target groups for PEPV have been close contacts of cases (i.e. sexual partners, household contacts, healthcare workers, and individuals with other prolonged physical or high-risk contact[1]). In the context of limited supply of vaccines, contacts with a high risk of developing severe disease if infected, such as children, pregnant women, and immunocompromised individuals, should be prioritised for PEPV based on a case-by-case risk assessment.

PEPV should be administered within four days of first exposure (and up to 14 days after exposure in the absence of symptoms). Thus, community engagement efforts for early identification of contacts of cases are very important.

Overall, vaccination programmes must be backed by thorough surveillance and contact tracing. Programmes should be accompanied by strong information campaigns and robust pharmacovigilance.

Special considerations in healthcare settings and home isolation

The principal mode of MPXV transmission is thought to be direct contact with mpox lesions or objects contaminated with lesions, such as clothing and bed linen (fomites). Therefore, caregivers and members of the household should avoid touching skin lesions with their bare hands, wear disposable gloves when handling materials which were in contact with the bare skin of a patient (including clothes, bed linen and towels), and observe strict hand hygiene before and after the use of gloves.

In healthcare settings, prevention of transmission is based on standard, contact and droplet infection control precautions during the care of symptomatic, suspected and confirmed mpox patients [18]. Mpox infection prevention and control guidance for primary and acute care settings have been developed by ECDC [87]. Detailed options are also available in guidance documents developed by the WHO [97] and the United Kingdom Health Security Agency (UKHSA) [98].

Safety of Substances of Human Origin

All potential donors of substances of human origin (SoHO) should be carefully interviewed regarding their contacts with infected mpox cases (confirmed or suspected), infected animals, or travels to affected areas. Data on the medical history of these risk factors should be collected in the case of deceased donors.  

Based on the incubation period of mpox, it is recommended to defer asymptomatic donors who have been in contact with mpox cases (confirmed or suspected) from SoHO donation, for a minimum of 21 days from the last day of exposure.

Since the mpox prodromal stage varies in duration (one to four days [2]) and symptoms can be non-specific and mild [99-102] or absent [21], careful examination of any possible signs of infection should be performed even after the expiration of the deferral period (at least 21 days from the last day of exposure). In the donor assessment process, attention should be paid to the wide range of clinical presentations of the disease as seen in the outbreak of 2022. These clinical presentations deviate from those observed in earlier outbreaks, in particular the asynchronous appearance and evolution of the skin lesions, and the presentation with a solitary lesion or mucosal lesions only [29]. Examinations should not overlook mild and non-specific signs like headache, fatigue or anogenital skin lesions. Due to the isolation of replication-competent virus from semen [67,103], for cases where there is a necessity to store semen (e.g. fertility preservation), it is advisable to perform PCR of the semen sample.

Special considerations to mitigate the risk of animal-to-human and human-to-animal transmission

To reduce animal-to-human transmission in areas with active MPXV circulation among wildlife, it is recommended to avoid contact with (potential) animal reservoirs as well as any materials that have been in contact with a potentially infected sick or dead animal.

Similarly, human cases of mpox should avoid close direct contact with animals including pet animals, livestock and wild animals (in captivity). Close contacts of cases should also avoid being in close direct contact with animals for 21 days after the last exposure to the virus. To mitigate the risk of wild animals getting in contact with the virus, waste, including medical waste, should be disposed of in a safe manner and should not be accessible to rodents and other scavenger animals.

[1] As defined in the ECDC guidance on Considerations for contact tracing during the monkeypox outbreak in Europe, 2022

Further reading

• Monkeypox factsheet, European Food Safety Authority (EFSA)
• Vaccines and immunization for monkeypox: Interim guidance, 16 November 2022, World Health Organization (WHO)

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