The changing epidemiology of human monkeypox—A potential threat? A systematic review

Abstract

Monkeypox, a zoonotic disease caused by an orthopoxvirus, results in a smallpox-like disease in humans. Since monkeypox in humans was initially diagnosed in 1970 in the Democratic Republic of the Congo (DRC), it has spread to other regions of Africa (primarily West and Central), and cases outside Africa have emerged in recent years. We conducted a systematic review of peer-reviewed and grey literature on how monkeypox epidemiology has evolved, with particular emphasis on the number of confirmed, probable, and/or possible cases, age at presentation, mortality, and geographical spread. The review is registered with PROSPERO (CRD42020208269). We identified 48 peer-reviewed articles and 18 grey literature sources for data extraction. The number of human monkeypox cases has been on the rise since the 1970s, with the most dramatic increases occurring in the DRC. The median age at presentation has increased from 4 (1970s) to 21 years (2010–2019). There was an overall case fatality rate of 8.7%, with a significant difference between clades—Central African 10.6% (95% CI: 8.4%– 13.3%) vs. West African 3.6% (95% CI: 1.7%– 6.8%). Since 2003, import- and travel-related spread outside of Africa has occasionally resulted in outbreaks. Interactions/activities with infected animals or individuals are risk behaviors associated with acquiring monkeypox. Our review shows an escalation of monkeypox cases, especially in the highly endemic DRC, a spread to other countries, and a growing median age from young children to young adults. These findings may be related to the cessation of smallpox vaccination, which provided some cross-protection against monkeypox, leading to increased human-to-human transmission. The appearance of outbreaks beyond Africa highlights the global relevance of the disease. Increased surveillance and detection of monkeypox cases are essential tools for understanding the continuously changing epidemiology of this resurging disease.

Multinational monkeypox outbreak: what do we know and what should we do?

“…Cases outside of Africa have historically been seldom encountered and typically associated with international travel or imported animals. In 2013, the epidemic potential of the disease was shown during the outbreak in the USA, where MPXV hitched a ride with a shipment of animals from Ghana to Illinois [ 5 ].…”

Investigating the monkeypox outbreak

“…All cases so far genotyped in Europe during the current outbreak are more closely related to the west African clade and to viruses exported from Nigeria to Israel, Singapore, and the UK in 2018 and 2019 1415. The west African clade has been associated with milder illness and a lower case fatality rate (roughly 4%) than the central African clade (roughly 10%) 7. If some infections are asymptomatic, as previously described,11 these estimates of case fatality could be too high.…”

“…Fourthly, we need to reassess what proportion of infections cause severe or fatal disease. Historically, two different genomic clades of monkeypox virus have been described in west and central Africa 7. All cases so far genotyped in Europe during the current outbreak are more closely related to the west African clade and to viruses exported from Nigeria to Israel, Singapore, and the UK in 2018 and 2019 1415.…”

“…The second is to investigate whether and how the spread of monkeypox is being driven by a rise in case numbers at source in west and central Africa. The number of monkeypox cases increased in Africa between 1970-79 and 2010-19 following the demise of smallpox and the decline in smallpox vaccination, especially in the Democratic Republic of the Congo (DRC) 67. This rise has included major outbreaks, the largest of which affected 17 states of Nigeria in 2017-18 89…”

The never-ending global emergence of viral zoonoses after COVID-19? The rising concern of monkeypox in Europe, North America and beyond

“…The clinical manifestations of Monkeypox resembles that of smallpox [ 16 ] including non-specific clinical features such as fever, chills, myalgia, headache, lethargy, and lymphadenopathy followed by a vesiculo-pustular rash, with an incubation period ranging from 5 to 21 days [ [26] , [27] , [28] , [29] ]. Even though the incubation period for this current outbreak has not been established, its often long period of incubation suggests that initial exposure events may have occurred in early April 2022.…”