Monkeypox

Mpox (formerly monkeypox) is an infectious disease caused by the monkeypox virus (MPXV), an enveloped double-stranded DNA virus classified within the Orthopoxvirus genus of the Poxviridae family. This viral family includes variola (smallpox), cowpox, and vaccinia viruses. The virus exists as two distinct clades: clade I (comprising subclades Ia and Ib) and clade II (comprising subclades IIa and IIb). A global outbreak of clade IIb commenced in 2022 and persists to the present day, while concurrent outbreaks of clades Ia and Ib are affecting the Democratic Republic of the Congo and other African nations, with clade Ib having spread beyond Africa as of August 2024. The natural reservoir of the virus remains unknown, though various small mammal species, including squirrels and monkeys, have demonstrated susceptibility to infection.

Mpox typically presents with a painful rash, enlarged lymph nodes, fever, headache, muscle ache, back pain, and low energy. Symptoms usually begin within one week of exposure but may manifest anywhere from 1 to 21 days post-contact, with the illness lasting 2 to 4 weeks in immunocompetent individuals and potentially longer in those with compromised immune systems. The characteristic rash often begins on the face before spreading to the palms of the hands and soles of the feet, though it may originate at the site of initial contact, including the genital region. Lesions progress from flat sores to fluid-filled blisters before crusting and healing. While most individuals recover fully, severe complications may include secondary bacterial infections, pneumonia, sepsis, encephalitis, and corneal infection leading to vision loss. Children, pregnant women, and immunocompromised persons face elevated risk of severe outcomes.

Mpox exhibits a complex epidemiological profile characterized by concurrent multi-clade outbreaks with distinct geographic distributions. The clade IIb outbreak that emerged in 2022 represents a sustained global phenomenon affecting numerous countries, including some African nations, with a relatively low case fatality rate estimated at 0.16% during the 2022-2023 period. In contrast, clade I outbreaks, particularly the ongoing epidemic in the Democratic Republic of the Congo as of April 2024, demonstrate substantially higher severity with a case fatality rate of approximately 4.9%. The emergence of clade Ib beyond African borders marks a significant expansion in geographic distribution. The true animal reservoir remains unidentified, though evidence suggests small mammals serve as potential amplification hosts in endemic settings.

Human-to-human transmission occurs primarily through close contact with infected individuals, encompassing skin-to-skin contact (including sexual contact), mouth-to-mouth or mouth-to-skin contact, and face-to-face exposure that may generate infectious respiratory particles. During the 2022 global outbreak, sexual contact emerged as the predominant transmission route. Individuals with multiple sexual partners face elevated acquisition risk. Environmental transmission via contaminated objects such as clothing or linens has been documented, as have needle injuries in healthcare settings and exposures in community settings including tattoo parlours. Zoonotic transmission occurs through physical contact with infected animals, including certain monkey species and terrestrial rodents such as tree squirrels, through bites, scratches, or handling of infected meat. Human-to-animal transmission (spillback) has been reported, including detection in pet dogs, though confirmation of true infection versus surface contamination remains pending.

Populations at elevated risk for mpox acquisition include individuals with multiple sexual partners, who face increased exposure probability during outbreaks with sexual transmission dynamics. Persons with compromised immune systems, whether due to medication, underlying medical conditions, or HIV infection, demonstrate heightened susceptibility to severe disease manifestations. Children and pregnant women represent vulnerable groups with increased risk of complicated clinical courses and adverse outcomes. Healthcare workers and individuals in settings involving animal handling or contact with potentially contaminated materials may face occupational exposure risks.

Prevention strategies center on vaccination and exposure reduction. Mpox vaccination is recommended for high-risk populations, particularly during outbreak periods, and may be administered as pre-exposure prophylaxis or post-exposure prophylaxis within 4 days of contact (and up to 14 days if no symptoms have developed). Infected individuals should isolate at home or in hospital for the duration of infectiousness, defined as from symptom onset until all lesions have crusted over and scabs have fallen off. Additional preventive measures include lesion covering, well-fitting mask use in the presence of others, and condom use during sexual activity (though this reduces but does not eliminate transmission risk from skin-to-skin or mouth-to-skin contact). Reducing zoonotic risk requires avoiding unprotected contact with wild animals, particularly sick or dead animals, and ensuring thorough cooking of animal meat in endemic areas.

Mpox surveillance requires clinical awareness given the disease's nonspecific initial presentation and overlap with other rash illnesses. Laboratory confirmation via polymerase chain reaction (PCR) detection of viral DNA from lesion samples represents the diagnostic standard. Differential diagnosis must exclude chickenpox, measles, bacterial skin infections, scabies, herpes, syphilis, other sexually transmitted infections, and medication-associated allergies. Co-infection with other STIs is possible. Case definitions should incorporate exposure history, characteristic rash progression, and geographic outbreak context. The presence of multiple circulating clades with differing virulence profiles necessitates clade-specific characterization where feasible for accurate epidemiological assessment and public health response calibration.

1. 1 WHO Fact Sheet. Mpox.
2. 2 WHO Q&A. Mpox.
3. 3 Wikidata. mpox.
4. 4 Wikipedia. Mpox - Wikipedia.

ICD-10

B04

ICD-11

1E71

Total cases

5K

Peak month

2024-09

Coverage

4 reporting countries · 2000-01-01 → 2026-05-09