Monkeypox outbreak predominantly affecting men who have sex with men, Madrid, Spain, 26 April to 16 June 2022

Monkeypox virus (MPXV) is an enveloped double-stranded DNA virus that belongs to the Orthopoxvirus genus of the Poxviridae family. There are two distinct genetic clades of the MPXV: the Central African (Congo Basin) clade and the West African clade. Monkeypox (MPX) is a viral zoonosis (a virus transmitted to humans from animals) with symptoms similar to those seen previously in smallpox patients, although it is clinically less severe. Transmission can occur from direct contact with the blood, bodily fluids, or cutaneous or mucosal lesions of infected animals. Human-to-human transmission can result from close contact with respiratory secretions, skin lesions of an infected person or recently contaminated objects [1]. Transmission via droplet respiratory particles usually requires prolonged face-to-face contact. With the eradication of smallpox in 1980 and subsequent cessation of smallpox vaccination, MPXV has emerged as the most important orthopoxvirus for public health [1].

Generally, outbreaks of MPX occur in countries from West and Central Africa [2,3] where, up to the 1980s, the transmission of the disease to humans has been mainly due to contact with animals. An increase in frequency was observed in the 1980s and, since the 1990s, there has been an increase in the number of secondary cases by contact with an infected person. Most cases observed outside of Africa were due to animal-to-human transmission, imported from an endemic country or associated with imported pets [4-6].

On 7 May 2022, the United Kingdom (UK) reported a case in a traveller from Nigeria. Between 13–16 May, six additional cases were reported, all of whom appeared to have been infected in London and self-identify as gay, bisexual or other men who have sex with men (MSM) [7,8]. On 18 May, Portugal reported the first 14 cases of MPX in men [9,10]. This is the first time that chains of person-to-person transmission of MPX have been reported in Europe, where no epidemiological links to West or Central Africa could be identified. Cases continue to be reported in several European countries [8,10,11]….