Last week, Singapore experienced its first case of monkeypox in the form of a tourist from Nigeria who developed symptoms only after having spent several days in town. Monkeypox is endemic in west and central Africa, probably maintained in multiple rodent populations with occasional animal-to-human transmission. An excellent review of human cases was published in the US CDC’s Morbidity and Mortality Weekly Report in March last year.

Screen capture from the US CDC MMWR report on monkeypox published in March 2018

The disease was brought to international attention in 2017 when large numbers of cases were reported in Nigeria at the end of that year, in particular 2 cases that were “exported” to the United Kingdom in September. As can be seen from the chart obtained from the Nigerian CDC’s January 2019 report, the number of human cases have fallen since 2017 although sporadic cases are reported virtually every month.

Screen capture from the NCDC January 2019 report – monkeypox cases in Nigeria.

Monkeypox was first identified in 1958 when an outbreak occurred among cynomolgus monkeys in Statens Serum Institut, Denmark. What several of my astute colleagues found when reading the source paper was that those monkeys had come from ….. Singapore! At this point in time, it is unclear if the monkeys were shipped through Singapore (as is more likely) or caught in Singapore and sent overseas (which seems less likely, although the particular monkey species is native to Singapore). A quick search revealed that illegal wildlife trade – including monkeys – was a major problem in Singapore even in the 1970s, although it is hard to believe that an established European institute would purchase the animals illegally. I have put up screenshots of the old article (behind a paywall) below. His team had described the 2 outbreaks (both sets of monkeys were from Singapore) in detail, including investigations to isolate the virus, which he described as being different from other poxviruses known at the time. The researchers were also able to infect other animals with the novel virus, including rabbits.

Screenshots from the original paper by Preben von Magnus describing monkeypox.

Curiously, just under a year later, the disease was again found in monkeys in a research laboratory in Philadelphia, USA. Although in this case, the authors did not describe where the monkeys had been obtained from. The article is also behind a paywall, whereas I could not find – much less access – the two accompanying articles (published in a different journal) that described their experimental work on the virus.

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About hsuliyang

I am an infectious diseases physician based in Singapore.

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Infectious diseases, Outbreak, Public Health, Singapore

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