Global mpox outbreak
There is currently an ongoing global outbreak across several countries with community transmission, multiple generations of spread, and new modes of transmission, which started in May 2022. The World Health Organization (WHO) declared that the outbreak constitutes a Public Health Emergency of International Concern (PHEIC) in July 2022. The public health emergency expired in the US on 31 January 2023. There may have been undetected transmission for some time prior to the outbreak.
Globally, over 84,000 confirmed cases and 81 deaths were from 110 countries/territories/areas between 1 January 2022 and 20 January 2023. The number of cases peaked in August 2022 and has since been steadily declining, likely due to behavioural modifications and vaccination, among other factors.
Outside of the African region, the outbreak is predominantly affecting gay, bisexual, and other men who have sex with men (MSM) who have reported recent sex with one or multiple male partners. The modes of transmission during sexual contact remain unclear, but available evidence indicates that the principal mode is through close contact with skin or mucosal lesions during sexual activity with a person with mpox. Currently, there is no signal of sustained transmission beyond these networks, although cases have been reported rarely in women and children.
The majority of reported cases have no established travel links to countries where the virus was historically known to be present. This is the first time that local transmission has been reported in newly-affected countries without epidemiological links to countries that have previously reported cases (i.e., West or Central Africa). The group of variants largely circulating in the outbreak belong to the Clade IIb variant of the monkeypox virus.
The clinical presentation has been atypical. Lesions tend to be localised to the genital, perineal/perianal, or perioral areas and often do not spread further. There may only be a few lesions, a single lesion, or no visible lesions. Lesions may be at different stages of development, and may appear before prodromal symptoms. Proctitis may be the only presenting symptom in some patients. While the majority of cases are mild, a small number of patients require hospital admission for symptom control or management of complications.
Mpox was historically known to be endemic in West and Central Africa. However, a global outbreak, which was first identified in May 2022, is currently ongoing in many countries. The epidemiology and clinical course has changed compared with previous outbreaks observed with endemic disease.
All suspected cases should be isolated immediately and the regional infectious diseases unit notified. Cases should be managed by experts, including public health officials, to prevent a potential emergency situation.
Historically, patients presented with a characteristic rash that progressed in sequential stages at the same stage of development. However, the rash in the current outbreak is atypical, with lesions generally localised to the genital, perineal/perianal, or perioral areas. Lesions may be few and at different stages of development. Symptoms such as fever, lymphadenopathy, headache, backache, and myalgia may appear before or after the rash, or not at all.
Many other conditions present in a similar way, so it is important to keep in mind possible differentials as these are far more likely to be the cause.
Usually a self-limiting illness with most patients recovering within 2 to 4 weeks. However, serious illness with severe complications can occur, particularly in children, pregnant women, and immunocompromised people.
Vaccines are available for pre- and post-exposure vaccination.
Mpox (formerly known as monkeypox) is a viral zoonotic disease caused by the monkeypox virus. The virus can be transmitted to humans from different wild animals, such as non-human primates and rodents, although its natural host reservoir is unknown. While animal-to-human transmission is the more common mode of transmission in endemic countries, human-to-human transmission does occur and has led to human outbreaks. The virus is a hazard group 3 pathogen.
The World Health Organization began using the new preferred term mpox as a synonym for monkeypox from November 2022. Mpox will become the preferred term, replacing monkeypox, after a transition period of one year.
History and exam
Key diagnostic factors
- anorectal symptoms
Other diagnostic factors
- sore throat
- recent travel to/living in endemic country or country with outbreak
- contact with suspected, probable, or confirmed case
- random one-time sexual encounters or multiple sexual partners
- recent tattoo or piercing
- contact with infected animal
- children (severe disease)
- pregnant women (severe disease)
- immunocompromised (severe disease)
- HIV infection (severe disease)
- acute or chronic skin conditions (severe disease)
- sexually transmitted infection
1st investigations to order
- polymerase chain reaction (PCR)
- urea and electrolytes
- sexually transmitted infection tests
Investigations to consider
- CT abdomen/pelvis
- blood culture
- malaria antigen test
David L. Heymann, MD, DTM&H
Professor of Infectious Disease Epidemiology
London School of Hygiene and Tropical Medicine
University of London
Centre on Global Health Security - Chatham House
DLH declares that he has no competing interests.
Dr David L. Heymann would like to gratefully acknowledge Dr Tom Blanchard, the previous contributor to this topic.
TB is the principal investigator on an MRC/Wellcome/Newton Fund grant to make a Zika vaccine based on recombinant modified vaccinia Ankara.
Miguel G. Madariaga, MD, MSc, FACP
Infectious Diseases Consultant
Naples Community Hospital
MGM declares that he has no competing interests.
Jimmy Whitworth, MD, FRCP, FFPH, FMedSci, DTM&H
London School of Hygiene & Tropical Medicine
JW declares that he has no competing interests.
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