Opinion article by Prof Felicity Burt , Prof Dominique Goedhals , Division of Virology at the University of the Free State (UFS), and Dr Charles Kotzé, National Health Laboratory Service (NHLS), Universitas Academic Hospital.

---

The recent COVID-19 pandemic has certainly highlighted the importance of vigilance and awareness of emerging diseases with public health implications. The monkeypox virus has recently made headlines, after the detection of more than 200 cases in geographically distinct regions. On 13 May, the World Health Organisation (WHO) was notified of human cases of the monkeypox disease occurring in the United Kingdom, outside of the known endemic region.

Exported cases have been detected previously and usually occur sporadically. In contrast, within the past two weeks, human cases have been confirmed in at least 21 countries, including various European countries, the United Kingdom, Israel, the Canary Islands, Canada and the United States, and Australia. The initial case appears to have been a traveller from Nigeria. Sequence data may help to determine if there have been multiple exportations from West Africa. 

What is monkeypox and what do we know about the aetiologic agent? Monkeypox is the name given to a disease caused by the monkeypox virus, a zoonotic pathogen endemic in Central and West Africa and responsible for cases of the disease in the endemic region, with occasional exported cases in travellers. The virus was initially identified in 1958 in monkeys housed at a research laboratory in Denmark, and the name monkeypox was derived from the appearance of lesions and the occurrence in monkeys. The first human case was identified 52 years ago in the Democratic Republic of the Congo. Since then, human monkeypox cases have been reported in several other Central and West African countries: Cameroon, the Central African Republic, Ivory Coast, the Democratic Republic of the Congo, Gabon, Liberia, Nigeria, Republic of the Congo, and Sierra Leone. The first monkeypox outbreak outside of Africa was in the United States of America in 2003 and was linked to contact with infected prairie dogs imported as exotic pets. Since then, there have been various small, contained outbreaks outside of Africa that have mostly been linked to the importation of the virus from African countries. 

The virus is related to the smallpox virus, which was eradicated in the 1970s by vaccination. Although belonging to the same family of viruses as the smallpox virus, the disease caused by monkeypox is less severe, with fewer fatalities.   Unlike smallpox, which carries a case fatality rate of 30%, the case fatality rate in monkeypox is low (estimated at 3-6% in more recent outbreaks).  There are two clades of the monkeypox virus: the West African clade and the Congo Basin (Central African) clade. In this outbreak, all of the cases have been linked to the West African clade of the monkeypox virus.

Transmission occurs from animal to human, and from human to human, through close contact with lesions, body fluids, and contaminated materials. The virus enters the body through the respiratory tract, mucous membranes, or broken skin.  The disease begins with non-specific symptoms such as fever, headache, muscle pains, and swollen lymph nodes. This is followed by the typical skin rash, which progresses through stages known as macules, then papules, vesicles, pustules, and lastly crusts or scabs. Lesions can also occur on mucous membranes such as the mouth, eye, and genital area.  The infectious period lasts through all stages of the rash, until all the scabs have fallen off. There are a number of other infectious and non-infectious conditions that need to be differentiated; therefore, individuals presenting with these symptoms will need to consult their doctor to determine whether a diagnosis of monkeypox needs to be considered. In the current outbreak, a number of the cases in the United Kingdom and Europe have been detected in men who have sex with men, during visits to sexual health clinics. This pattern of spread has not previously been described and it remains to be determined whether the spread has occurred through close person-to-person contact or through sexual transmission.  

To date, no cases have been detected in South Africa, but the recent global spread of the severe acute respiratory syndrome coronavirus 2 (SARS_CoV-2) highlights the ability of pathogens to spread. The National Institute for Communicable Diseases (NICD) in Johannesburg offers a specialised diagnostic service for the monkeypox virus, using molecular assays and electron microscopy. 

Vaccination against the smallpox virus is believed to offer 85% protection against monkeypox, hence older persons should have some protection; however, vaccination against smallpox was phased out globally following the eradication of smallpox during the 1970s. A more recently developed vaccine against monkeypox is available but has very limited availability.  No specific antivirals are available with proven efficacy in clinical trials.

While the monkeypox virus can be spread via the respiratory route, this occurs in the form of large droplets, rather than aerosol transmission, which is seen with SARS-CoV-2 (causing COVID-19). Aerosols are smaller particles that can remain suspended in the air for prolonged periods, facilitating the transmission of SARS-CoV-2. Monkeypox is therefore less contagious than COVID-19, as close contact is required for longer periods.  For this reason, many experts around the world predict that this outbreak will not spread like SARS-CoV-2. The importation of monkeypox to South Africa is a definite possibility, because South Africa is a significant economic and travel hub for Africa. Previous outbreaks of monkeypox in non-endemic areas have been interrupted by contact tracing and isolation, which was very effective in controlling further spread.  Heightened vigilance is therefore needed for the early detection of such cases.