Printed on: December 21st, 2024

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Mpox (monkeypox)

Mpox (monkeypox)

In August 2024, the World Health Organization declared mpox a “public health emergency of international concern” due to rapid spread of a new virus strain (clade Ib) in the Democratic Republic of the Congo (DRC).

Monkeypox was renamed mpox by the World Health Organization in November 2022. In this article, where the reference we are using predates the name change, we have kept the original name for clarity of referencing.

This article was last reviewed in August 2024.

Mpox is a pox virus, similar to smallpox. Following a flu-like prodromal phase, mpox typically presents with a rash, which can sometimes be widespread and severe. It was previously confined to West and Central Africa but, since May 2022, there has been international spread.

In August 2024, the WHO raised the alert about the rapid spread of a new, highly virulent clade Ib strain of mpox virus circulating in the DRC, with new evidence of spread to areas in Central and East Africa and of sexual transmission.

• This strain of mpox is classified as a public health emergency of international concern.
• The risk to the UK population is considered low.
• There have been no cases of clade I mpox identified in the UK up to 22/08/2024 (gov.uk – WHO declares mpox outbreak a public health emergency of international concern).  

There are 2 major subtypes (clades) of mpox:

• Clade I (Central African and Congo basin origin, more severe).
• Clade II (West African origin, less severe).

Clade I subtype mpox is classified in the UK as a ‘high consequence infectious disease (HCID)’, unlike clade II (gov.uk – HCID status of mpox (monkeypox)). The majority of the cases seen in the 2022 outbreak were clade II subtype.

In the UK, rates of mpox infection were highest in 2022 (3732 cases) and fell significantly in 2023–24 (196 cases from Jan 23 to May 24) (gov.uk – mpox (monkeypox) outbreak: epidemiological overview, 9 May 2024).

The UK control strategy for outbreak management is to eliminate person-to-person mpox transmission in the UK (gov.uk – UK strategy for mpox control 2022 to 2023).

In this article, we outline the UKHSA case definition of mpox, the process for clinical assessment of potential clade I mpox and the actions suggested for primary care. We also draw on a BMJ descriptive case series which outlined some of the clinical features we should be aware of, a JAMA viewpoint article and associated editorial, and an NEJM review (BMJ 2022;378:e072410, JAMA 2022;328:139, JAMA 2022;327:2278, NEJM 2022;387:1783).

Mpox is spread via respiratory droplets, contact with lesions or via fomites. It can also result from close contact with an infected animal (primarily rodents). In the UK, no animals have been found to carry mpox.

Incubation is between 5 and 21 days, with the rash typically presenting 1–5 days after the onset of a flu-like febrile prodrome.  

Typical skin lesions will develop as macules; these progress into papules and then vesicles, before crusting over and healing. Pustules can develop.

• The rash predominantly affects the face, hands, feet (including soles and palms), mucous membranes and genitals.
• Duration is usually around 2–4 weeks before all lesions have healed (JAMA 2022;328:2,139).

The lesions are contagious until all scabs have fallen off and there is intact skin underneath.

The UKHSA case definitions of mpox are divided into PROBABLE case and POSSIBLE case:

If we suspect a possible case of clade 1 mpox, we should:

• Isolate the patient in a single room with a closed door.
• Wear appropriate PPE (see below) and provide the patient with the same level of PPE.
• Discuss with local infection specialists for advice on safe transfer into secondary care and immediate infection control precautions to protect our staff, patients and ourselves.

See gov.uk – clade 1 mpox virus infection, updated 16/08/2024.  

The BMJ case series highlighted some important variations in the clinical presentation of the 2022 mpox outbreak compared with the usual case definition (BMJ 2022;378:e072410):

• Usually, mpox is a biphasic illness with a prodrome of fever, enlarged lymph nodes and myalgia, with the rash appearing 2–4 days later. However, in the 2022 outbreak, this appeared to be reversed, and the febrile illness often appeared after the initial lesions.
• Presenting features included penile oedema and rectal pain or pain on defecation; this is not part of the usual case definition.
• Sore throat +/- tonsillar abscess also appeared to be more common in the 2022 outbreak than was previously seen in mpox.
• The NEJM review also highlighted epiglottitis as a feature of the 2022 mpox variant (NEJM 2022;387:1783).

While anyone can catch mpox, a BMJ Practice Pointer reminds us that certain groups are at higher risk (BMJ 2023;380:e073352):

• People identifying as men who have sex with men (MSM).
• Those engaging in high-risk sexual behaviour.
• Occupational exposure in health workers and laboratory staff.
• Those exposed to animal reservoirs (such as poorly cooked, infected meat).

Mpox has a mortality rate of 1–11% (JAMA 2022;328:2,139). Clade I mpox is considered higher risk.

A greater risk of complications is seen in pregnant individuals, those under the age of 8y and those with immune compromise (JAMA 2022;328:2,139). The BMJ Practice Pointer also notes that individuals with severe pre-existing exfoliative skin disease (such as severe eczema, psoriasis, acne, widespread herpes or burns) are at increased risk of adverse outcomes (BMJ 2023;380:e073352).

The BMJ case series reminds us that complications include (BMJ 2022;378:e072410):

• Secondary skin infection.
• Pneumonia.
• Ocular disease which can lead to loss of vision.
• Encephalitis.

All confirmed or highly-probable cases of mpox should be notified to local health protection teams.

Treatment is symptomatic because there are no specific antivirals available for mpox. Individuals with high risk of complications may be offered antivirals or IVIG in secondary care (JAMA 2022;328:2,139).

The information and advice provided in this section is aimed at the care of those with non-HCID clade II mpox. Any possible clade 1 case should be isolated and discussed with infectious disease specialists (gov.uk – clade I mpox virus infection).

Consider admission for those (BMJ 2023;380:e073352):

• With severe disease (sepsis, pneumonitis, encephalitis).
• With widely-disseminated lesions.
• With suspected involvement of the cornea.
• With refractory pain or swelling.
• At high risk of complications.
• Living with high-risk individuals who are unable to self-isolate.

For those with non-HCID mpox who are at lower risk of complications, we can advise self-care:

• Self-isolate until rash is resolved, scabs have fallen off and intact skin has formed (see full UKHSA quarantine advice in table below).
• Wear a mask when self-isolating, if not alone.
  • Provide advice on infection control measures, avoiding close contact with other household members and not sharing bed linen or towels.
• Symptom management:
  • Discuss antipyretics and analgesia for fever and pain, good hydration and to keep skin clean.
  • Safety-net to seek medical attention for: general deterioration, vomiting, painful cervical lymphadenopathy causing dysphagia, poor oral intake, eye pain or vision problems, difficulty passing urine or stool
  • Consider topical local anaesthetics or stool softeners to aid with proctalgia or pain on passing urine.
• Reducing risk:
  • Avoid contact lens use.
  • Avoid shaving areas affected by rash.
  • Use a condom for 12 weeks after resolution of symptoms and scabs.

For assessment of a probable or suspected case of non-HCID mpox, the National Infection Prevention and Control Manual for England advises that we wear aprons, gloves and a fluid-resistant surgical mask, and provide the patient with the same. If the patient has respiratory symptoms, the mask should be upgraded to a fit-tested FFP3 respirator mask (gov.uk – principles for control of non-HCID mpox in the UK: 4 nations consensus statement, accessed August 2024).  

For a possible case of clade 1 mpox, clinicians should wear appropriate HCID PPE NHS England - addendum on high consequence infectious disease (HCID) personal protective equipment (PPE), accessed August 2024).

Because it is unlikely we will have access to this level of PPE in primary care, we are advised to isolate the patient in a single room with a closed door, and discuss with local infection specialists for advice on safe transfer into secondary care and immediate infection control precautions to protect our staff, patients and ourselves (gov.uk - clade 1 mpox virus infection, updated 16/08/2024).

Any potential cases should be discussed with your local sexual health, infectious diseases or microbiology colleagues (depending on pathways in your area). If testing is advised: ensure you are wearing PPE as above; a PCR viral swab should be taken from a lesion; the risk of mpox should be clearly indicated on the sample; and laboratories should be informed in advance of the sample. All samples with confirmed mpox will be sent for clade testing at the rare and imported pathogens laboratory (gov.uk – mpox: diagnostic testing, accessed August 2024).

The UKHSA has provided contact tracing guidance for non-HCID clade 1 mpox cases, which would be the remit of local health protection teams. Actions following possible mpox contact depends on how close the contact with the index case was, and can be found here: gov.uk publishing service – monkeypox contact tracing classification and vaccination matrix version 17, 23 January 2023, accessed August 2024).  

There is no licensed mpox vaccine. The licensed smallpox vaccine Imvanex is in use in the UK to reduce transmission of mpox. The following is a summary of the English vaccination programme as of November 2022, drawing on the Joint Committee on Vaccination and Immunisations (JCVI) advice in the Green Book (gov.uk - Green Book chapter 29: smallpox and monkeypox, September 2022). This guidance has not yet been updated following the 2024 clade I mpox outbreak. We recommend that individual advice from local infectious diseases specialists is taken for these patients.

The JCVI has advised that gay and bisexual men, and other men who have sex with men, at highest risk should be offered pre-exposure vaccination via sexual health centres. When considering who is 'at highest risk', the advice is to use the same groups eligible for PrEP for HIV, regardless of HIV status:

• Those with multiple partners.
• Those with recent (within the past 12m) bacterial STI.
• Those who visit 'sex on premises' venues.

In addition to these groups, pre-exposure vaccination will be offered to occupational staff working in 'high consequence infectious disease' units, sexual health staff working with populations considered to be at risk, and laboratory staff working with high-risk samples.

The usual programme of pre-exposure vaccination would be 2 doses a minimum of 28 days apart. This can be offered to people considered to be at ongoing risk of re-exposure (e.g. healthcare and laboratory workers) when supplies allow.

There is some limited evidence that post-exposure vaccination can reduce severity of symptoms.

Vaccination should be offered to 'high-risk' contacts of non-HCID mpox (using the table above), ideally within 4 days of exposure. Vaccination may be offered up to 14 days post-exposure for those with high risk of complications: pregnant individuals, those under the age of 10y and those with immune compromise.

A single dose is advised for post-exposure vaccination.

Mpox (monkeypox) Mpox is spread via respiratory droplets, contact with lesions and via fomites. Incubation is between 5 and 21 days. Consider the diagnosis in patients who have febrile illness with any of: a suspicious rash; a history of contact with mpox; a new sexual partner in the past 21d; or in men who have sex with men. Consider the possibility of the more severe clade I HCID mpox in those with symptoms and a history of travel to at-risk countries, including the DRC. Confirmed cases should use a condom for 12 weeks after resolution of symptoms and scabs. PPE is advised for clinicians seeing patients with suspected mpox. Quarantine and contact tracing guidance has been provided by the UKHSA to minimise risk of transmission. Isolate until all scabs have fallen off and intact skin is revealed. The UK is following a targeted vaccination programme of higher-risk individuals and post-exposure vaccination.

Useful resources: Websites (all resources are hyperlinked for ease of use in Red Whale Knowledge) Terence Higgins Trust – monkeypox in the UK UKHSA - monkeypox: contact information sheet for category 3 contacts UKHSA – monkeypox: contact information sheet for category 2 contacts