Mpox (formerly known as monkeypox)^[4] is an infectious viral disease that can occur in humans and some other animals.^[5] Symptoms include a rash that forms blisters and then crusts over, fever, and swollen lymph nodes.^[5] The illness is usually mild and most of those infected will recover within a few weeks without treatment.^[6] The time from exposure to onset of symptoms ranges from five to twenty-one days and symptoms typically last from two to four weeks.^[7] Cases may be severe, especially in children, pregnant women or people with suppressed immune systems.^[8]

The disease is caused by the monkeypox virus,^{[lower-alpha 1]} a zoonotic virus in the genus Orthopoxvirus. The variola virus, the causative agent of the disease smallpox, is also in this genus.^[5] Human-to-human transmission can occur through direct contact with infected skin or body fluids, including sexual contact.^[5] People remain infectious from the onset of symptoms until all the lesions have scabbed and healed.^[8] It may spread from infected animals by handling infected meat or via bites or scratches.^[8] Diagnosis can be confirmed by PCR testing a lesion for the virus' DNA.^[5]

An outbreak of mpox, a viral disease then commonly known as "monkeypox", was confirmed in May 2022.^[9] The initial cluster of cases was found in the United Kingdom,^[10] where the first case was detected in London on 6 May 2022^[11] in a patient with a recent travel history from Nigeria (where the disease is endemic).^[12] On 16 May, the UK Health Security Agency (UKHSA) confirmed four new cases with no link to travel to a country where mpox is endemic.^[11] Subsequently, cases have been reported from many countries and regions.^[13] The outbreak marked the first time mpox had spread widely outside Central and West Africa. There is evidence that the disease had been circulating and evolving in human hosts over a number of years prior to the outbreak.^[14]

On 23 July 2022, the Director-General of the World Health Organization (WHO), Tedros Adhanom Ghebreyesus, declared the outbreak a public health emergency of international concern (PHEIC), stating that "we have an outbreak that has spread around the world rapidly, through new modes of transmission, about which we understand too little".^[15] A global response to the outbreak included public awareness campaigns in order to reduce spread of the disease, and repurposing of smallpox vaccines.^[16][17] In May 2023, the World Health Organization declared an end to the PHEIC, citing steady progress in controlling the spread of the disease.^[18]