Monkeypox (Human)

Primary reference(s)

WHO, 2019. Monkeypox. World Health Organization (WHO). Accessed 13 December 2019.

Additional scientific description

Monkeypox is a viral zoonosis (a virus transmitted to humans from animals) with symptoms similar to those seen in the past in smallpox patients, although it is clinically less severe. It is caused by an orthopoxvirus, from the family of viruses which also caused human smallpox (WHO, 2018). With the eradication of smallpox in 1980 and subsequent cessation of smallpox vaccination, monkeypox has emerged as the most important orthopoxvirus. Monkeypox occurs in Central and West Africa, often in proximity to tropical rainforests (WHO, 2019a).

Monkeypox is mostly transmitted to people from various wild animals such as rodents and primates, with limited secondary spread through human-to-human transmission. Monkeypox is less contagious than smallpox but can be fatal in 1% to 10% of cases (WHO, 2018).

Common symptoms include fever, intense headache, lymphadenopathy, back pain, myalgia and weakness. Like in smallpox, rashes appear beginning on the face and spreading on the body, including to the palms of the hands and soles of the feet (WHO, 2018).

Human monkeypox was first identified in humans in 1970 in the Democratic Republic of the Congo (then known as Zaire) in a 9-year-old boy in a region where smallpox had been eliminated in 1968. Since then, most cases have been reported from rural, rainforest regions of the Congo Basin, particularly in the Democratic Republic of the Congo, where it is considered to be endemic (WHO, 2019a).

Since 1970, human cases of monkeypox have been reported from 11 African countries – Benin, Cameroon, the Central African Republic, the Democratic Republic of the Congo, Gabon, Ivory Coast, Liberia, Nigeria, the Republic of the Congo, Sierra Leone, and South Sudan. In 2017, Nigeria experienced the largest documented outbreak, 40 years after the last confirmed case. The true burden of monkeypox is not known. For example, in 1996–1997, a major monkeypox outbreak was suspected in the Democratic Republic of Congo but with a lower case fatality and a higher attack rate than usual. Some patient samples tested positive for varicella virus and some contained both varicella and monkeypox viruses. Concurrent outbreaks of chickenpox and monkeypox could explain a change in transmission dynamics in this case (WHO, 2019a).

The virus has been exported from Africa a few times. In spring 2003, monkeypox cases were confirmed in the USA. Most patients were reported to have had close contact with pet prairie dogs that were infected by African rodents that had been imported into the country from Ghana. Recently, monkeypox was carried to Israel in September 2018, to the UK in September 2018 and December 2019, and to Singapore in May 2019 by travellers from Nigeria who fell ill with monkeypox after arrival (WHO, 2019a).

Two distinct genetic clades of the virus have been identified – the Congo Basin and the West African clades – with the former found to be more virulent and transmissible. The geographic division between the two clades is thought to be in Cameroon as this is the only country where both monkeypox virus clades have been detected (WHO, 2019a).

Monkeypox can only be diagnosed definitively in the laboratory by polymerase chain reaction (PCR) on skin lesion specimens, genetic sequencing or by viral isolation (WHO, 2020).

Metrics and numeric limits

The https://who.int| the US Centers for Disease Control and Prevention, and the governments of Nigeria and the Democratic Republic of Congo have published guidance on case classification and surveillance standards (CDC, 2003; Osadebe et al., 2017; WHO, 2019b; Nigeria Centre for Disease Control, 2020).

Examples of drivers, outcomes and risk management

Exposure to body fluids or skin lesions or eating inadequately cooked meat of infected animals is a possible risk factor (WHO, 2017).

Secondary, or human-to-human, transmission can result from close contact with infected respiratory tract secretions, skin lesions of an infected person or objects recently contaminated by patient fluids or lesion materials. Transmission occurs primarily via respiratory droplets or mucous membranes, usually requiring prolonged face-to-face contact, which puts household members of active cases at greater risk of infection. Transmission can also occur by inoculation or via the placenta as in congenital monkeypox (WHO, 2017).

Surveillance and rapid identification of new cases is critical for outbreak containment (WHO, 2017).

Infection in people can be reduced by raising awareness of the risk factors and educating people about measures they can take to reduce exposure to the virus. Control measures include isolation of affected persons, good respiratory and hand hygiene, and other personal protective measures. Those at highest risk, such as health workers or laboratory personnel, can be protected through vaccination. A vaccine against monkeypox was licensed in 2019 (WHO, 2019b, 2020).

Health workers caring for patients with suspected or confirmed monkeypox virus infection, or handling specimens from them, should implement standard and droplet infection control precautions (WHO, 2018).