Clinical‐epidemiological aspects of the Monkeypox 2022 epidemic: A multicentre study by the Italian SIDeMaST Group of Sexually Transmitted, Infectious and Tropical Diseases

Before April 2022, monkeypox virus infection in humans was seldom reported outside African regions where it is endemic. Currently, cases are occurring worldwide. Transmission, risk factors, clinical presentation, and outcomes of infection are poorly defined.

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.

Following two reports of monkeypox virus infection in individuals who returned from Nigeria to the USA, one who returned to Texas (July 2021) and the other to the Washington, DC area (November 2021), the number of monkeypox infection have dramatically increased. This sounded an alarm of potential for spreading of the virus throughout the USA. During 2022, there was a report of monkeypox virus infection (May 6, 2022) in a British national following a visit to Nigeria who developed readily recognizable signs and symptoms of monkeypox virus infection. Soon following this report, case numbers climbed. By June 10, 2022, more than 1,500 cases were reported in 43 countries, including Europe and North America. While the prevalence of the monkeypox virus is well known in central and western Africa, its presence in the developed world has raised disturbing signs for worldwide spread. While infection was reported during the past half-century, starting in the Democratic Republic of Congo in 1970, in the United States, only sporadic monkeypox cases have been reported. All cases have been linked to international travel or through African animal imports. The monkeypox virus is transmitted through contact with infected skin, body fluids, or respiratory droplets. The virus spreads from oral and nasopharyngeal fluid exchanges or by intradermal injection; then rapidly replicates at the inoculation site with spreads to adjacent lymph nodes. Monkeypox disease begins with constitutional symptoms that include fever, chills, headache, muscle aches, backache, and fatigue. Phylogenetically the virus has two clades. One clade emerged from West Africa and the other in the Congo Basin of Central Africa. During the most recent outbreak, the identity of the reservoir host or the primary carriage remains unknown. African rodents are the suspected intermediate hosts. At the same time, the Centers for Disease Control (CDC) affirmed that there are no specific treatments for the 2022 monkeypox virus infection; existing antivirals shown to be effective against smallpox may slow monkeypox spread. A smallpox vaccine JYNNEOS (Imvamune or Imvanex) may also be used to prevent infection. The World Health Organization (WHO), has warned that the world could be facing a formidable infectious disease challenge in light of the current status of worldwide affairs. These affairs include the SARS-COVID-19 pandemic and the Ukraine-Russia war. In addition, the recent rise in case of numbers worldwide could continue to pose an international threat. With this in mind, strategies to mitigate the spread of monkeypox virus are warranted.