Preben von Magnus et al. describe two outbreaks of a non-fatal pox-like disease in cynomolgus monkeys that had recently been received from Singapore at the Statens Seruminstitut, Copenhagen, Denmark (von Magnus 1959). Subsequent outbreaks, field surveys and experimental studies revealed that the monkeypox virus (MPXV) had the capacity to infect and cause high levels of mortality and morbidity in a broad spectrum of hosts from across the globe (Parker 2013). The natural host of MPXV is probably squirrels, for example F. anerythrus (Khodakevich 1986).
Ladnyj et al. report the first case of human monkeypox infection admitted to Basankusu Hospital on 1 September (Ladnyj 1972). The patient was a 9-month-old boy who became ill with fever on 22 August 1970 and 2 days later developed a rash. “On examination it was recorded that the lesions were haemorrhagic, although they showed a centrifugal distribution typical of smallpox. Crusts were collected for laboratory examination. The rash lasted about 2 weeks. During the scabbing stage the patient developed otitis and mastoiditis as well as enlarged, painful cervical nodes, which were subsequently incised and drained. The patient recovered and was about to be discharged but on 23 October he developed measles and died 6 days later. The child had never been vaccinated.”
The Weekly Epidemiological Record publishes the report of a 35 year old man, a citizen of Benin, [who] developed a rash on 22 November 1978 in Omifounfoun village, Oyo State, Nigeria, where he was temporarily living. He had been in Omifounfoun from September 1978 until 3 December 1978 as a seasonal worker. The patient had not previously been vaccinated against smallpox. He was hospitalized in Parakou town, Benin, on 5 December 1978 upon his return from Nigeria (Anonymous 19790420)
From 1970 to 1979, 47 cases of human monkeypox occur in 5 Central and West African countries, 38 of these cases in Zaire. Breman reports that the evolution of the illness and the sequelae of monkeypox and smallpox are the same(Breman 1980): “Monkeypox has a case-fatality rate of about 17%. Children below 10 years of age comprise 83% of the cases. All cases have occurred in tropical rainforest areas and clustering of cases has been observed in certain zones within countries and within families. Person-to-person spread may have occurred in 4 cases; the secondary attack rate among susceptible, very close family members was 7.5% (3 cases/40 contacts) and among all susceptible contacts was 3.3% (4 cases/123 contacts)—much lower than the 25-40% secondary attack rate that occurs with smallpox. Although the low transmission rate and the low frequency of disease indicate that monkeypox is not a public health problem, more data are needed.”
Figure 1.1 – Distribution of tropical rainforest and 47 human monkeypox cases, 1970-79 (Breman 1980).
Figure 1.2 – Distribution of 31 monkeypox cases in northwestern and central Zaire, 1970-79 (Breman 1980).
1996-1997 Democratic Republic of Congo
Outbreak in the Democratic Republic of Congo. The first investigation of 88 cases found a case-fatality rate of 3.7% (Hutin 1997). A second paper describes 419 possible or probable case. Out of 344 cases which occurred in one health zone (Katako Kombe), 85% were in children under 16 years of age. “Thirty-one per cent had had moderate or severe rash, i.e. more than 100 skin lesions, and in 41% the eruption lasted longer than one week. Fever, diarrhoea, cervical lympadenopathy, sore throat and mouth ulcers were the most common symptoms. Ten were hospitalised for up to 30 days and 54% were incapacitated for more than three days. Five died (case fatality ratio 1.5%). These individuals ranged in age from four to eight years and all died within three weeks of rash onset. Twenty had scar evidence of vaccinia vaccination and 19 reported a past history of chicken pox.” (WHO 19971114, CDC 19971212)
2003 United States of America
In this first outbreak of monkeypox infections in humans outside Africa, rodents imported from Ghana had probably infected prairie dogs (Cynomys ludovicianus) that were being kept as pets. Approximately 110 prairie dogs were sold and 15 became ill, of which ten died rapidly (Parker 2013).
Eleven days after being bitten by one of her pet prairie dogs, a 3-year-old girl in Wisconsin on 24 May 2003 became the first person to be diagnosed with monkeypox in this outbreak. Two months later, her parents and dozens other people in the United States had suspected or confirmed cases (CDC 20030711, Cohen 2022). Human MPXV infection was associated with handling of MPXV-infected animals and exposure to excretions and secretions of infected animals (Reynolds 2007). There were no deaths and only 3 persons developing serious illness. There is a thorough clinical discussion of the first cases available (Reed 2004).