May 25, 2022 


WHO and other health organizations are alarmed at the recent global outbreak of monkeypox. As of May 21, 2022, more than 80 cases of monkeypox have been confirmed in at least 12 countries outside of Africa (1). The first case of the disease in the UK was reported on May 7, in a patient who had recently travelled to Nigeria. Since then, sporadic outbreaks of monkeypox have been reported in the UK, Spain, Portugal and other European countries, Australia, Canada, and the US. Monkeypox primarily occurs in Central and West Africa with a few thousand cases per year on average (2). Cases outside Africa have been limited in the past to a handful that are associated with travel to Africa or with the importation of infected animals (3). Strikingly, in the past week alone, the number of cases detected in non-African countries has already surpassed the number of average cases. More suspected cases are under investigation, suggesting greater increases in the number of monkeypox cases globally.


Monkeypox is a zoonotic disease caused by a Poxvirus known as monkeypox (4). The virus is closely related to smallpox and vaccinia viruses. Monkeypox disease results in a smallpox-like disease in humans, although it is less severe than smallpox. In general, symptoms begin with fever, headache, muscle pains, and feeling tired. A rash usually appears 1–3 days after the onset of fever and lymphadenopathy, with lesions appearing simultaneously, and evolving at a similar rate (5). Their distribution is mainly peripheral but can cover the whole body during a severe illness. Monkeypox is usually a self-limited disease, with the symptoms lasting from 2 to 4 weeks. Severe cases occur more commonly among children and are related to the extent of virus exposure (2).

It is estimated that smallpox vaccination was approximately 85% protective against monkeypox (6). The waning population immunity associated with discontinuation of smallpox vaccination after its successful eradication has led to the resurgence of monkeypox in African countries, such the Democratic Republic of the Congo and Nigeria (7). In addition, deforestation has increased the interface of animals and humans. Animal hosts include rodents and non-human primates (2). Human-to-human transmission is relatively inefficient, resulting from close contact with respiratory secretions, skin lesions of an infected person, or recently contaminated objects. In general, outbreaks occur occasionally in sub-Saharan Africa after someone comes in contact with an infected wild animal, and infected travelers sometimes carry the disease to other countries (8, 9).


There are two distinct genetic clades of the monkeypox virus: the West African clade and the Central African (Congo Basin) clade (10). The West African clade demonstrates a case fatality rate (CFR) <1%, and no human-to-human transmission was documented previously. In contrast, the Central African clade shows a CFR up to 11% and causes more severe disease and human-to-human transmission. Current global outbreaks are caused by the West African clade. Some monkeyvirus associated with the current outbreak has shown to be related to the West African clade, although it is no clear if they represent mutant strains with increased transmissibility or pathogenicity. (11). Most of the cases have lesions, exclusively perigenital, perianal, and around the mouth (9). Almost all of the cases include men aged 20–50, many of whom are gay, bisexual, and have sex with men (11). It is unclear whether sexual transmission is a contributing factor to current outbreak (9). One of the hypotheses is its transmission after close contact with lesions. Further analysis needs to be completed to identify the origin of the outbreaks, routes of transmission, and the risk factors for infection. For preventive measures, two vaccines that protect against smallpox and monkeypox are available in Europe and North America (11). One vaccine (ACAM2000) is similar to the vaccine used during the smallpox eradication campaign. The other vaccine (Jynneos) uses a nonreplicating form of vaccinia and is explicitly approved for monkeypox. Although some drugs have been licensed for the treatment of smallpox, little is known about their effect on monkeypox. (8). Clinical care for monkeypox should be fully optimized to isolate patients, alleviate symptoms, manage complications, and prevent long-term sequelae (2).


The current outbreak of monkeypox shows unusual characteristics. Limited information on epidemiology, sources of infection, and transmission patterns make it difficult to predict the impact of monkeypox outbreaks on public health amid the resurgence of COVID-19 cases. A key strategy will be efficient containment of viral spread with increased genomic surveillance and diagnostics. This will also help us understand the dynamic transmission of resurging monkeypox globally.


  1. BBC. Monkeypox: 80 cases confirmed in 12 countries.
  2. WHO. Monkeypox.
  3. Nature. Monkeypox goes global: why scientists are on alert.
  4. Shchelkunov SN, Marennikova SS, Moyer RW. Orthopovxiruses Pathogenic for Humans. Chapter: Classification of Poxviruses and Brief Characterization of the Genus. New York, NY: Springer (2005)
  5. Ladnyi ID, Jezek Z, Fenner F, Henderson DA, Arita I. Smallpox and its Eradication Chapter: Human Monkeypox and Other Poxvirus Infections of Man. Geneva: World Health Organization (1988).
  6. Fine PE, Jezek Z, Grab B, Dixon H. The transmission potential of monkeypox virus in human populations. Int J Epidemiol. 1988; 17(3):643–650.
  7. Bunge EM, Hoet B, Chen L, Lienert F, Weidenthaler H, Baer LR, Steffen R. The changing epidemiology of human monkeypox-A potential threat? A systematic review. PLoS Negl Trop Dis. 2022 Feb 11;16(2):e0010141. doi: 10.1371/journal.pntd.0010141. PMID: 35148313; PMCID: PMC8870502.
  8. CDC. Monkeypox.
  9. Science. Monkeypox outbreak questions intensify as cases soar.
  10. Sklenovská N, Van Ranst M. Emergence of Monkeypox as the Most Important Orthopoxvirus Infection in Humans. Front Public Health. 2018 Sep 4;6:241.
  11. Nature. Monkeypox goes global: why scientists are on alert.

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