The changing epidemiology of monkeypox and preventive measures: an update

Archives of Virology (2023) 168:31 https://doi.org/10.1007/s00705-022-05677-3 REVIEW The changing epidemiology of monkeypox and preventive measures: an update Sasidharanpillai Sabeena1 Received: 3 September 2022 / Accepted: 14 October 2022 / Published online: 5 January 2023 © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2022 Abstract Monkeypox is a systemic exanthematous viral disease presenting with fever, lymphadenopathy, and vesicular rash. The zoonotic virus causing this disease is endemic to many sub-Saharan African countries, where a steady rise in cases has been witnessed for the past 30 years. However, monkeypox re-emerged as the largest outbreak of the West African clade (clade II) of monkeypox virus in Nigeria in 2017. This poxvirus received only minimal global attention until recently, when cases emerged in Europe and rapidly spread globally in certain sections of the community, such as men having sex with men or bisexuals, with human-to-human transmission. Monkeypox virus has established its presence in humans, crossing geographical boundaries, and clusters of infections may occur among individuals in close contact. All six WHO regions have reported monkeypox cases without any epidemiological association with endemic regions. The ongoing multicountry outbreak suggests that silent human-to-human transmission has been happening in Europe and the United States for a while. For containment of the outbreak, active surveillance and rapid identification of new cases are essential. The availability of vaccines is currently limited. Policymakers must focus on awareness programmes, primary preventive or post-exposure vaccination, and treatment with antivirals to control the ongoing outbreak. Introduction Monkeypox virus (MPXV) infection has re-emerged as the predominant orthopox infection in humans since the eradication of smallpox in many African countries, and in 2022, it emerged in almost all non-endemic regions, further expanding its geographical spread. Monkeypox, a smallpox-like disease, is caused by MPXV, an enveloped double-stranded DNA virus belonging to the genus Orthopoxvirus of the family Poxviridae. This virus was discovered by Magnus et al. in 1959, causing pox outbreaks in cynomolgus monkeys used for polio vaccine research at Statens Serum Institut, Copenhagen, Denmark [1]. Even though their clinical manifestations are similar in humans and non-human primates, smallpox virus (variola virus) and MPXV are distinct poxviruses with common ancestors [2]. Handling Editor: William G Dundon. * Sasidharanpillai Sabeena 1 Allure Residency, Near the British School, Kathmandu 44600, Nepal On July 23, 2022, the recent monkeypox outbreak was declared a public health emergency of international concern (PHEIC) by the World Health Organization (WHO). By then, the global burden was 17,186 cases in 75 countries in all six WHO regions and five deaths in non-endemic countries. As per the WHO Fourth External Situation Report, there were 41,664 laboratory-confirmed cases and 12 deaths in 96 countries by August 24, 2022. After an increase in laboratory-confirmed cases for four consecutive weeks globally, cases declined by 21% by the last week of August. The WHO Sixth External Situation Report on September 21 noted 61,753 laboratory-confirmed cases and 23 deaths in 105 countries since January 2022 [3]. For the past seven decades, this self-limiting zoonosis has been reported mainly in the rural rainforest areas of Central and West Africa. A change in the epidemiology was perceived in the last decade, with an increase in human-tohuman transmission and a shift in the median age at presentation from 4 to 21 years [4]. Based on genomic analysis of MPXV DNA sequences from Central Africa, West Africa, and the USA, two clades, namely the Central African or the Congo Basin (CB) clade (renamed clade I) and the West African (WA) clade (renamed clade II) have been reported. Clade I strains have been shown to be more virulent than 13 Vol.:(0123456789) 31 Page 2 of 11 clade II strains [5–8]. Under clade II, there are two subclades: clade IIa and clade IIb. A group of variants circulating in 2022 were classified as subclade IIb (https://www. who.int/news/item/12-08-2022-monkeypox-exper ts-give- virus-variants-new-names). Historical West African strains belong to clade IIa, while Nigerian strains from 2017-2019 and all of the published sequences from the 2022 outbreak belong to clade IIb [9]. Within clade IIb, the Pango lineage system is used to name lineages, with designations such as A.1, A.2 or B.1. The case fatality rate of the Central African clade (clade 1) ranges from 0 to 11%, and that of the West African clade (clade IIa) is around 3-6%. Currently, the case fatality rate in the ongoing monkeypox outbreak of 2022 caused by clade IIb is 0.03% (https://www.who.int/emergencies/disease- outbreak-news/item/2022-DON390). The Democratic Republic of the Congo (DRC) reported the first case of human infection in a 9-month-old boy in 1970, although the virus had been isolated from monkeys already in 1952 [10]. This zoonotic virus was found to have a broad host range [11]. WHO considers even a single case of confirmed monkeypox in a country to be an outbreak(https://www.who.int/emergencies/disease-outbr eak-news/item/2022-DON393). The appearance of several cases in non-endemic regions without any epidemiological association with endemic areas suggests that silent transmission had been occurring for a while. The last two decades have witnessed an increase in human monkeypox disease attributed to the termination of smallpox vaccination, deforestation, human encroachment on wildlife habitats, contact with exotic pets, rapid urbanization, a rise in the number of immunocompromised individuals, and growth in international air travel. Based on observational studies in Africa, smallpox vaccination provides about 85% protection against monkeypox [12]. After the termination of smallpox vaccination in 1980, WHO actively supported monkeypox surveillance from 1981 to 1986. However, infrequent reporting in later years contributed to sparse information on the geographical spread and exact burden of monkeypox. Compared to the WHO operational surveillance data from1981 to 1986, the DRC reported a 20-fold rise in monkeypox incidence between 2005 and 2007 [13]. Monkeypox virus infection in animals Many small mammals, including monkeys, prairie dogs, hedgehogs, anteaters, squirrels, dogs, and shrews are susceptible to MPXV infection [14, 15]. Although the precise animal reservoir is unknown, MPXV often circulates in Central and West African environments without causing clinical signs in mammals such as rope squirrels, sun squirrels, giant pouched rats, and African dormice. 13 S. Sabeena Certain species of squirrels and rufous-nosed rats have been reported to be seropositive for MPXV [16]. Other mammals, such as domestic pigs (Sus scrofa) and rhesu (...truncated)