Monkeypox

Abstract

Monkeypox is a zoonotic illness caused by the monkeypox virus, an Orthopoxvirus in the same genus as the variola, vaccinia, and cowpox viruses. Since the detection of the first human case in the Democratic Republic of the Congo in 1970, the disease has caused sporadic infections and outbreaks, mainly restricted to some countries in west and central Africa. In July, 2022, WHO declared monkeypox a Public Health Emergency of International Concern, on account of the unprecedented global spread of the disease outside previously endemic countries in Africa and the need for global solidarity to address this previously neglected disease. The 2022 outbreak has been primarily associated with close intimate contact (including sexual activity) and most cases have been diagnosed among men who have sex with men, who often present with novel epidemiological and clinical characteristics. In the 2022 outbreak, the incubation period ranges from 7 days to 10 days and most patients present with a systemic illness that includes fever and myalgia and a characteristic rash, with papules that evolve to vesicles, pustules, and crusts in the genital, anal, or oral regions and often involve the mucosa. Complications that require medical treatment (eg, antiviral therapy, antibacterials, and pain control) occur in up to 40% of patients and include rectal pain, odynophagia, penile oedema, and skin and anorectal abscesses. Most patients have a self-limited illness; between 1% and 13% require hospital admission (for treatment or isolation), and the case-fatality rate is less than 0·1%. A diagnosis can be made through the presence of Orthopoxvirus DNA in PCRs from lesion swabs or body fluids. Patients with severe manifestations and people at risk of severe disease (eg, immunosuppressed people) could benefit from antiviral treatment (eg, tecovirimat). The current strategy for post-exposure prophylaxis or pre-exposure prophylaxis for people at high risk is vaccination with the non-replicating modified vaccinia Ankara. Antiviral treatment and vaccines are not yet available in endemic countries in Africa.

Figure 1

Proposed mechanism for the spread of the monkeypox virus throughout the body and its relation to the transmission route The clinical presentation of monkeypox might be influenced by microorganism virulence factors, host immunity, and the transmission route. Unlike in previous outbreaks, the monkeypox virus in the 2022 outbreak is thought to spread through close contact or sexual contact, causing predominantly localised lesions instead of extensive disseminated lesions. It is possible that the localised nature of the disease results in lower concentrations of viraemia and, consequently, less virus in respiratory excretions. As the respiratory route becomes less important, transmission continues to occur through direct contact via dermal inoculation, perpetuating the cycle of clinical presentation and transmission. Nevertheless, the monkeypox virus in previous outbreaks, mainly from the Democratic Republic of the Congo, is thought to be transmitted primarily through the respiratory tract and was followed by disseminated disease presentation. Both the dermal inoculation and respiratory routes could contribute to animal-to-human transmission. The size of the green arrows indicates the frequency of manifestation; a large arrow indicates a frequent pathway and a small arrow indicates an infrequent pathway.

Figure 2

Monkeypox clinical presentations and differential diagnosis Discrete rash on the thorax caused by monkeypox (Nigeria; A) and varicella (Spain; B); a generalised monkeypox rash (Democratic Republic of the Congo; C) and a blistering rash caused by dermatitis herpetiformis (Spain; D); localised monkeypox lesions causing penile oedema (Spain; E) and impetigo associated with scabies (Malawi; F); localised perianal rash caused by monkeypox (Spain; G) and molluscum contagiosum (Spain, H); a solitary monkeypox genital ulcer (Spain; I) and a primary syphilis chancre (Spain; J); lip lesion caused by monkeypox (Spain; K) and herpes simplex (Spain; L); hand lesions caused by monkeypox (Spain; M) and Orf virus infection (Spain; N); monkeypox lesions on the tongue (Spain; O) and aphthous ulcer on the labial mucosa (Spain; P). Photo credits: Dimie Ogoina (A), Fernando Gruber (B), Cristina Galván (C, D, F, H, N, P), Adrià Mendoza (E), José Miguel Cabrera (G, K, O), Irene Fuertes (I, M), Martí Vall-Mayans (J), and Rosa Taberner (L).