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Conditions · Infectious and tropical diseases

Mpox !

Mpox is a viral infection spread by close contact that causes painful skin sores and swollen lymph nodes, sometimes with fever.

Updated 2026-11-01

Structures involved

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Microorganisms that cause it

Why it happens

What it is

Infection by the monkeypox virus, an orthopoxvirus related to smallpox, that causes a febrile illness with lymphadenopathy and a rash of firm, deep lesions that progress through stages over 2–4 weeks.

Who gets it

Endemic in Central and West Africa (clade I and IIa). The 2022–2023 global outbreak, caused by clade IIb, spread mainly through sexual contact, largely among men who have sex with men. Colombia was one of the most affected countries in the Americas, with several thousand confirmed cases and a high proportion of people living with HIV; clade Ib has caused new spread since 2024.

Causes

  • Monkeypox virus (Orthopoxvirus); clades I (Ia, Ib) and II (IIa, IIb)
  • Close skin-to-skin, mouth-to-skin and sexual contact with lesions or body fluids
  • Respiratory secretions during prolonged face-to-face contact
  • Contaminated bedding, towels and clothing; needle injuries in health care
  • Infected animals (rodents, primates) and mother-to-fetus transmission

Risk factors

  • Multiple or new sexual partners, including men who have sex with men in outbreak networks
  • Household contact with a case
  • Health workers without adequate protection
  • Uncontrolled HIV (severe disease)
  • Pregnancy, young children and skin conditions such as eczema (severe disease)

Pathophysiology

The virus replicates at the entry site and in regional lymph nodes, then spreads in the blood to the skin and mucosa. Lesions form in the epidermis through ballooning degeneration of keratinocytes, evolving from macule to papule, vesicle, umbilicated pustule and crust. Unlike smallpox and varicella, prominent lymphadenopathy is typical. Contagiousness lasts from symptom onset until all crusts have fallen and new skin has formed.

Classification

  • By clade: clade I (historically more severe) and clade II (2022 outbreak: IIb)
  • Classic form: prodrome then centrifugal rash
  • Outbreak form: few localised anogenital or oral lesions, often without prodrome
  • Severe form: extensive, necrotising or disseminated disease in advanced HIV

Symptoms and signs

  • Fever, headache, muscle and back pain and fatigue (may precede or follow the rash)
  • Swollen, tender lymph nodes (inguinal, cervical)
  • Firm, well-defined, painful lesions that evolve to umbilicated pustules and crusts
  • Lesions on the genitals, anus, mouth, face, hands and feet
  • Rectal pain, tenesmus and bleeding (proctitis)
  • Sore throat and painful swallowing

Diagnosis

Clinical
Suspected in a person with a typical rash or anogenital lesions plus lymphadenopathy and a compatible exposure. HIV and other sexually transmitted infections are tested in every case.
Tests
PCR for viral DNA on swabs of lesion surface or fluid (throat or anal swabs if no lesions); blood and antibody tests are not recommended for diagnosis. Screening for HIV, syphilis, gonorrhoea, chlamydia and hepatitis.
Imaging
Not routinely needed; used for complications such as deep abscess or pneumonia.

Differential diagnosis

  • Varicella
  • Herpes simplex infection
  • Primary or secondary syphilis
  • Molluscum contagiosum
  • Hand, foot and mouth disease and bacterial skin infection

Goal of treatment

Control pain, care for the skin and mucosa, prevent complications and transmission, and treat severe or high-risk cases with antivirals.

Treatment

Conservative
Supportive care: analgesia (including for proctitis and oral pain), hydration, lesion hygiene, avoid scratching, and treat bacterial superinfection.
Medical
Antivirals developed for smallpox (such as tecovirimat) are considered for severe disease or high-risk patients, usually under protocols, as their benefit is uncertain; continue or start antiretroviral therapy in people with HIV.
Follow-up
Isolation until all crusts have fallen and new skin has formed; contact and droplet precautions with respirator, gown, gloves and eye protection for health workers; contact tracing and follow-up for 21 days.
Medical
Vaccination with a non-replicating smallpox/mpox vaccine for high-risk people and as post-exposure prophylaxis, ideally within 4 days of exposure.

Complications

  • Bacterial skin infection and scarring
  • Proctitis with severe pain and rectal bleeding
  • Keratitis and corneal scarring
  • Pneumonia, encephalitis and sepsis
  • Necrotising disseminated disease in advanced HIV
  • Fetal loss when acquired in pregnancy

Prognosis

Clade IIb infection is usually self-limited over 2–4 weeks with low mortality, concentrated in people with uncontrolled HIV. Clade I has historically had higher fatality, especially in children in endemic areas.

Prevention

  • Vaccination of people at high risk and post-exposure vaccination of contacts
  • Avoid skin and sexual contact with people with lesions; temporary abstinence while lesions are present
  • Do not share bedding, towels or utensils with a case; hand hygiene
  • Health-care infection control and early case isolation

Test yourself

Think of the answer, then tap the question to see it.

Which clinical sign helps distinguish mpox from smallpox and varicella?

Prominent, tender lymphadenopathy.

What is the preferred diagnostic test for mpox?

PCR for viral DNA on swabs taken from the lesions.

When is a person with mpox no longer contagious?

When all crusts have fallen off and a fresh layer of skin has formed, usually 2–4 weeks.

Which other infections should be tested in every mpox case?

HIV and other sexually transmitted infections such as syphilis, gonorrhoea and chlamydia.

Which mpox clade caused the 2022 global outbreak?

Clade IIb.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Mpox (World Health Organization, 2024); Mpox: MedlinePlus (MedlinePlus (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.

Skin highlighted on the Durgical 3D model