Pathogen
Monkeypox virus (MPXV) is an enveloped DNA virus of the genus Orthopoxvirus. It is related to the human smallpox viruses and the cowpox viruses. MPXV is the causative agent of monkeypox (Mpox), a zoonosis. The disease manifests itself with a rash similar to that of smallpox, but is usually milder. MPXV clade 1 (case fatality rate 1 - 12 %) is endemic in Central Africa, clade 2 (case fatality rate < 0,1 %) in West Africa. Between 2022 and 2023, a global outbreak of monkeypox was caused by clade 2 b [1-6]. Reservoir animals of the virus in the endemic areas are presumably various rodents and small mammals. Monkeys and humans are regarded as incidental hosts [1-5].
Zoonotic transmission occurs through contact with the lesions or biological fluids and through handling meat from infected animals or contaminated objects [1-5]. MPXV can pass from person to person through contact with body fluids of an infected person, such as blood, saliva, mucus, or with the virus-containing skin lesions. Vertical infection in endemic areas and indirect transmission via contaminated surfaces also play a role. Infection through respiratory secretions is possible. MPXV has been detected in seminal fluid [1-4].
MPXV enters the host mainly via small skin lesions and the mucous membranes, probably also via the respiratory tract. The virus migrates to the nearby lymph nodes and multiplies there (primary viraemia), then infects distant lymph nodes and organs such as the spleen and liver (secondary viraemia). It can then spread to the lungs, kidneys, intestines and skin [1, 3-5].
Disease, symptoms
The incubation period in endemic areas is around 5 to 21 days; it is shorter (1 to 4 days) during infections of the 2022 outbreak [1-5].
In the prodromal phase (1 - 4 days), symptoms include fever, muscle aches, sore throat and headaches, fatigue and lymphadenopathy [1-6]. In infected persons in the 2022 outbreak, systemic symptoms may also occur after the skin lesions or be absent [1-3, 6].
The skin rash in the classic course often affects the entire body, starting on the face, then spreading to the trunk, arms and legs and finally to the hands and feet [1-6]. In addition to cutaneous efflorescences, those affected by the 2022 outbreak mainly suffer from anogenital and perioral lesions [1-3, 6]. The number of skin lesions varies from a few to over 1000; in the course of the 2022 outbreak, most patients have up to 20 lesions [2, 3].
The efflorescences go through the stages of macules, papules, vesicles and pustules until crusts develop [1, 2, 4-6]. Infected persons are contagious from the onset of symptoms until the lesions have completely healed [1, 3-5]. In adults, the disease is usually self-limiting after 2 to 4 weeks [1-4, 6].
Severe courses are observed in children, pregnant women and immunocompromised patients. The most common complications are bacterial superinfections of the skin, as well as broncho-pneumonia, dehydration, respiratory distress, encephalitis, proctitis, pneumonia and sepsis [1-6]. The mucosal lesions usually lead to severe pain [1-3]. Serious consequences of the disease can include facial scarring and, in the case of eye involvement, scarring of the cornea and even loss of vision [1-6].
Distribution
The first case of Mpox was described in 1970 in a 9-month-old boy in the Democratic Republic of Congo. Since then, infections have been reported particularly in Nigeria, Cameroon, the Democratic Republic of the Congo and the Republic of the Congo [1-6]. From 1 January to 12 November 2023, 12,569 suspected Mpox cases with 581 deaths were reported to the WHO from the Democratic Republic of the Congo [7]. Sporadic infections occurred in Europe, North America and Asia between 2003 and 2022 [1-3, 5].
Since May 2022, cases without a history of travel to known endemic areas have been recorded in various European countries such as Spain, France, the UK, Germany, Portugal and Italy, as well as in the USA, Brazil, Colombia, Mexico, Peru and China, mostly in men who have sex with men [1-6]. The WHO therefore declared a public health emergency of international concern on 23 July 2022 (ended on 14 April 2023). By 31 December 2023, 93,030 confirmed and 652 probable Mpox infections with 176 deaths had been reported to the WHO [6].
Diagnosis
The diagnosis of Mpox is based on nucleic acid detection of the virus using a PCR test in swabs of skin lesions [1, 3, 4]. Serology (immunofluorescence test, ELISA or neutralisation test to determine the antibody titer against orthopox viruses) can be used to support the diagnosis [1, 3, 4]. Orthopox-specific IgG appears 2 days after the onset of the rash and persists for several decades. Specific IgM can be detected from day 4 to day 77 post infectionem [8]. Specific IgG is measured in 2 serum samples, with the first one obtained during the first week of infection and the second one at least 3 weeks later [3].
The differential diagnosis should consider chickenpox, syphilis, Herpes simplex infections, infections due to other poxviruses as well as other sexually transmitted infections [1-3, 6].