The infection
Mpox, formerly monkeypox, is caused by an orthopoxvirus related to smallpox. Long confined to parts of central and west Africa, it spread worldwide in 2022, largely within sexual networks among men who have sex with men. A second outbreak, caused by a different and more severe clade, prompted a new international health emergency in 2024 in central and east Africa. Mpox is not classically an STI, but sexual contact has become its main route of transmission in several outbreaks.
Key facts
| Organism | Orthopoxvirus, several clades of differing severity |
|---|---|
| Incubation | 5 to 21 days, usually about a week |
| Infectious period | From the onset of symptoms until every scab has fallen |
| Diagnosis | PCR on a swab from a lesion |
| Treatment | Mainly supportive; antivirals reserved for severe disease |
| Vaccine | Yes, a third-generation smallpox vaccine, two doses |
| Duration | Two to four weeks in most cases |
How it is transmitted
Transmission occurs through direct prolonged contact with the skin lesions or mucous membranes of an infected person, which includes sex above all. Respiratory droplets play a role during prolonged face-to-face contact. Contaminated linen, bedding and towels can also transmit it. Transmission from mother to baby during pregnancy is possible.
Symptoms
The illness combines fever, muscle pain, marked fatigue and prominent swollen glands — a useful feature distinguishing it from other rashes. The rash progresses from flat lesions to blisters and then pustules that become umbilicated before crusting. In recent outbreaks lesions have frequently been confined to the genital, anal and oral areas, sometimes few in number, with severe anal pain or difficulty swallowing. The rash may precede the fever.
Testing
Diagnosis is by PCR on a swab from a lesion, so you need to be seen while the rash is present. For genital or anal lesions the differential diagnosis includes syphilis, herpes and other infections: a full screen is justified. Serology has little role in routine practice.
Treatment
Care is primarily supportive: pain relief, often necessary and sometimes inadequate with anal or throat involvement, local care and hydration. Antivirals exist, but a clinical trial conducted in central Africa in 2024 found no reduction in the time to lesion resolution; their use remains reserved for severe disease and immunosuppressed patients, in specialist settings.
If left untreated
Most episodes resolve within two to four weeks. Complications mainly affect immunosuppressed people, particularly those with uncontrolled HIV, in whom necrotic forms can be severe. Other reported complications are skin superinfection, permanent scarring, eye involvement and, more rarely, neurological disease. Anal pain can be disabling and warrants energetic analgesia.
Prevention
- Vaccination with a third-generation smallpox vaccine, two doses, is recommended for those most exposed.
- It can also be given after exposure, ideally within four days and up to fourteen.
- Condoms are not sufficient: transmission is by skin contact beyond the area they cover.
- With lesions present, avoid close contact and do not share linen, towels or bedding until scabs have fallen.
What has changed recently
An outbreak caused by a distinct clade led the World Health Organization to declare a public health emergency of international concern in 2024, centred on central and east Africa, with a substantial share of non-sexual transmission, including among children.
After a diagnosis
- Avoid close skin contact until every scab has fallen and the skin has healed.
- Notify recent partners so they can watch for lesions and be vaccinated.
- Have a full screen for other sexually transmitted infections.
- Seek care promptly for severe anal pain, difficulty swallowing or eye involvement.
Worth remembering
Any isolated genital or anal lesion, however small and unremarkable, can be mpox. Do not wait for a widespread rash to make the diagnosis: recent cases are often very localised.
A little history
The virus was discovered in 1958 in Copenhagen, at the State Serum Institute, in laboratory macaques imported for polio vaccine research — hence the name "monkeypox", although the natural reservoir is made up of African rodents. The first human case was identified in 1970 in a nine-month-old infant in Basankusu, in the Democratic Republic of the Congo, at a time when the smallpox eradication campaign was making doctors alert to any suspicious rash.
For fifty years the disease remained confined to the forests of Central and West Africa, with a few exports: in 2003, 47 cases in the United States from prairie dogs contaminated by rodents imported from Ghana. Nigeria saw a resurgence in 2017. The end of smallpox vaccination, which also protected against this virus, left whole generations without immunity.
In May 2022 the virus began circulating worldwide, mainly through sexual contact between men: more than 100,000 cases in a year, a public health emergency of international concern from July 2022 to May 2023, and the new name "mpox" adopted by the WHO in November 2022 to avoid stigma. A second emergency, declared in August 2024 over a more severe clade spreading from the DRC, was lifted in September 2025. The MVA-BN vaccine, approved in 2019, and the antiviral tecovirimat are today's tools.
How this differs between countries
The contrast is stark: vaccine is plentiful where the outbreak is small, and scarce where it kills most people.
- Vaccine access. High-income countries hold stocks and offer vaccination to those most exposed; in the countries affected by the 2024 outbreak, doses remained insufficient for a long time.
- Who is affected. In the global 2022 outbreak transmission was mainly sexual, among men who have sex with men; in the 2024 outbreak in central and east Africa a large share of cases involve children and household contacts.
- Clades. The circulating variants differ in severity, which explains very different complication rates between regions.
- Antivirals. A trial conducted in 2024 found no reduction in time to lesion resolution, leading several countries to reserve these drugs for severe disease.
- Isolation. Recommended durations vary, but the principle is the same everywhere: until every scab has fallen.