Guidance

Mpox (monkeypox): background information

The epidemiology, symptoms, diagnosis and management of monkeypox virus infections.

See the mpox collection page for further resources including guidance for health professionals.

Epidemiology

Mpox is a rare disease that is caused by infection with monkeypox virus (MPXV).

Mpox was first discovered in 1958 when outbreaks of a pox-like disease occurred in monkeys kept for research. The first human case was recorded in 1970 in the Democratic Republic of the Congo (DRC), and since then the infection has been reported in a number of central and western African countries. Prior to 2022 most cases were reported from the DRC and Nigeria.

In 2003, mpox was recorded in the US when an outbreak occurred following the importation of rodents from Africa. Cases were reported in both humans and pet prairie dogs. All the human infections followed contact with an infected pet exposed to an imported animal and all patients recovered.

Since May 2022, cases of human mpox have been reported in multiple countries that have not previously had MPXV in animal or human populations, including the UK.

There are 2 major genetic groups (clades) of MPXV, Clade I (formerly known as Central African or Congo basin clade) and Clade II (formerly known as West African clade). Clade II is split into Clade IIb and Clade IIa, with subgroup clusters called lineages. The majority of the cases seen in the outbreak in 2022 were from Clade IIb, lineage B.1.

Since January 2023, Clade II mpox is no longer considered a high consequence infectious disease (HCID) within the UK. Clade I mpox remains an HCID. There is further information on the HCID status of mpox available.

2022

Latest updates on cases of mpox identified in the UK.

As of 31 May 2023, over 3,700 cases of mpox have been identified in the UK since 7 May 2022. The majority of these cases have been from the Clade II B.1 lineage and have occurred in gay, bisexual, and other men who have sex with men (GBMSM) without documented history of travel to endemic countries. Further information on the epidemiology of these cases is available in the mpox epidemiological overview and the mpox technical briefings.

During 2022, a small number of non-B.1 cases have also been identified following recent travel.

Between 2018 and 2021, there were 7 cases of mpox in the UK. Of these, 4 were imported and 2 were cases in household contacts. One case was a healthcare worker involved in the care of one of these cases and was infected following contact with contaminated bed linen. This is the only documented healthcare worker acquisition, and the risk to healthcare workers is extremely low. There was no documented community transmission in these outbreaks.

Transmission

Mpox does not spread easily between people unless there is very close contact.

Spread of mpox may occur when a person comes into close contact with an infected animal (rodents are believed to be the primary animal reservoir for transmission to humans), human, or materials contaminated with the virus. Mpox has not been detected in animals in the UK.

The virus is transmitted through skin-to-skin contact, breathing in virus through the respiratory tract, or contact with mucous membranes (eyes, nose, mouth, genitals).

Person-to-person spread may occur through:

  • direct contact with skin lesions or scabs (including during sexual contact, kissing, cuddling or other skin-to-skin contact)
  • coughing or sneezing of someone who has mpox when they’re close to you
  • contact with clothing or linens (such as bedding or towels) used by someone with mpox

Clinical features

The incubation period is the duration/time between contact with the person with mpox and the time that the first symptoms appear. The incubation period for mpox is between 5 and 21 days.

Mpox infection is usually a self-limiting illness and most people recover within several weeks. However, severe illness can occur in some individuals.

The illness begins with:

  • fever
  • headache
  • muscle aches
  • backache
  • swollen lymph nodes
  • chills
  • exhaustion
  • joint pain

However, not all people who have mpox experience all of these symptoms. Within 1 to 5 days after the appearance of fever, a rash develops, often beginning on the face then spreading to other parts of the body including the soles of the feet and palms of the hands. Lesions can also affect the mouth, genitals and anus. The rash changes and goes through different stages before finally forming scabs which eventually fall off.

Some individuals may not have a widespread rash, and in some cases only genital lesions are present. These may be blisters/vesicles, scabs or ulcers.

An individual is contagious until all the scabs have fallen off and there is intact skin underneath. The scabs may also contain infectious virus material.

Images of individual mpox lesions

Notes

Areas of erythema and/or skin hyperpigmentation are often seen around discrete lesions.

Lesions can vary in size and may be larger than those shown.

Lesions of different appearances and stages may be seen at the same point in time.

Detached scabs may be considerably smaller than the original lesion.

Diagnosis

Clinical diagnosis of mpox can be difficult, and it is often confused with other infections such as chickenpox. A definite diagnosis of mpox requires assessment by a health professional and specific testing in a specialist laboratory.

In the UK, testing is provided by many NHS laboratories, and is also available at the Rare and imported pathogens laboratory (RIPL) at the UK Health Security Agency (UKHSA) Porton Down.

Patients with a travel or exposure history indicating possible Clade I (HCID) mpox should be discussed with the RIPL clinical team as soon as possible via the 24/7 Imported Fever Service helpline (0844 778 8990).

Samples from suspected and confirmed cases of mpox should be shipped as Category B diagnostic samples. See guidance on diagnostic testing for information on how to submit samples for testing.

Treatment

Treatment for mpox is mainly supportive. The illness is usually mild and most of those infected will recover within a few weeks without treatment.

Antiviral drugs such as cidofovir and tecovirimat can be used to treat mpox patients with severe disease or those who are at high risk of severe disease.

Smallpox vaccine can be used to support the control of outbreaks of mpox.

Vaccination against smallpox can be given both pre-exposure and is also effective if given as soon as possible post-exposure, and is up to 85% effective in preventing mpox. People vaccinated against smallpox in childhood may experience a milder disease.

Infection prevention and control

Prevention of transmission of infection by respiratory and contact routes is required. Appropriate precautions are essential for suspected and confirmed cases. Scabs are also infectious and care must be taken to avoid infection through handling bedding and clothing. Information on infection prevention and control measures are available in the National infection prevention and control manual for England.

Mpox virus is classified as an ACDP Hazard Group 3 pathogen and all laboratory work with live virus must be conducted at full Containment level 3 (CL3), in accordance with the Control of Substances Hazardous to Health Regulations 2002 (as amended). See the guidance on diagnostic testing for further information on handling specific sample types.

Laboratories must ensure that appropriate controls commensurate to CL3 are in place to minimise risk to laboratory workers so that they can safely perform laboratory tests that are essential to clinical care.

Further information

See WHO factsheet.

Additional mpox resources are also available on GOV.UK, including information on case definitions, contact tracing and vaccination.

Published 8 September 2018
Last updated 6 July 2023 + show all updates
  1. Updated information on epidemiology, transmission, clinical features and diagnosis.

  2. Updated to align with current epidemiology and diagnostic testing advice.

  3. Updated information on submitting samples for testing.

  4. Updated images of monkeypox lesions.

  5. Added link to monkeypox guidance, moved guidance for primary care to monkeypox guidance page, and removed guidance for environmental cleaning and decontamination (incorporated into 'Principles for monkeypox control in the UK', available on guidance page).

  6. Withdrew guidance for environmental cleaning and decontamination.

  7. Updated guidance.

  8. Added links to additional monkeypox guidance.

  9. Updated guidance.

  10. Updated with monkeypox case in England in December 2019.

  11. Updated cleaning and decontamination guidance (v4).

  12. Updated guidance on decontamination and cleaning.

  13. Updated guidance for cleaning and decontamination.

  14. Added guidance on environmental cleaning and decontamination.

  15. Added primary care guidance.

  16. First published.