More than 120 confirmed or suspected cases of monkeypox, a rare viral disease seldom detected outside of Africa, have been reported in at least 11 non-African countries in the past week. The emergence of the virus in separate populations across the world where it doesn’t usually appear has alarmed scientists — and sent them racing for answers.
“It’s eye-opening to see this kind of spread,” says Anne Rimini, an epidemiologist at the University of California, Los Angeles, who has studied monkeypox in the Democratic Republic of the Congo for more than a decade.
It is called monkeypox because researchers first detected it in laboratory monkeys in 1958, the virus is thought instead to transmit from wild animals such as rodents to people — or infected people. In an average year, a few thousand cases occur in Africa, typically in the western and central parts of the continent. But cases outside Africa have been limited to a handful that's associated with travel to Africa or with the importation of infected animals. The number of cases detected outside of Africa in the past week alone — which is all but certain to increase — has already surpassed the number detected outside the continent since 1970, when the virus was first identified as causing disease in humans. This rapid spread is what has scientists on high alert.
But monkeypox is no SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, says Jay Hooper, a virologist at the US Army Medical Research Institute of Infectious Diseases in Fort Derrick, Maryland. It doesn’t transmit from person to person as readily, and because it is related to the smallpox virus, there are already treatments and vaccines on hand for curbing its spread. So while scientists are concerned, because any new viral behavior is worrying — they are not panicked.
What researchers can tell from this preliminary genetic data is that the monkeypox virus is related to a viral strain predominantly found in western Africa. This strain causes milder disease and has a lower death rate — about 1% in poor, rural populations — compared with the one that circulates in Central Africa. But exactly how much the strain causing the current outbreaks differs from the one in western Africa — and whether the viruses popping up in various countries are linked to one another — remains unknown.
Answers to those questions could help determine if the sudden uptick in cases stems from a mutation that allows this monkeypox virus to transmit more readily than those of the past and if each of the outbreaks traces back to a single origin, says Reinna MacIntyre, an infectious disease epidemiologist at the University of New South Wales in Sydney, Australia. Unlike SARS-CoV-2, a rapidly-evolving RNA virus whose variants have regularly eluded immunity from vaccines and prior infection, monkeypox virus is a relatively large DNA virus. DNA viruses are better at detecting and repairing mutations than RNA viruses, which means it’s unlikely that the monkeypox virus has suddenly mutated to become adept at human transmission, MacIntyre says.
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