The monkeypox virus, now diagnosed in hundreds of people in 26 countries, may have been quietly circulating for years before its sudden emergence worldwide, scientists have theorised.
Infectious disease experts and scientists at genetic labs are urgently looking for clues to explain why a virus that has been found in West Africa for half a century and typically doesn’t spread readily from person to person made such a dramatic and troubling appearance in the past month.
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“There may have been undetected transmission for a while,” said Rosamund Lewis, the World Health Organisation’s technical lead for monkeypox during a briefing last week.
“What we don’t know is how long that may have been. We don’t know if it’s weeks, months or possibly a couple of years.”
At the University of Leuven in Belgium, virology professor Marc Van Ranst said his laboratory’s sequencing revealed genetic mutations of the virus that were “limited” and “none of them are smoking guns”.
“Everybody is interested in more complete genomes to get an idea about quite an important question: How long have these viruses been circulation, under the radar?” Van Ranst said.
“I think nobody believes this jumped out of Africa a couple of weeks ago.”
University of Edinburgh scientists recently sequenced samples from the outbreak and posted their findings on May 30.
The samples they investigated descended from a version of monkeypox that was identified in Singapore, Israel, Nigeria and the United Kingdom between 2017 and 2019.
While the investigators did identify an “unexpectedly large number” of changes to the virus’s genetic code since that time, some experts do not believe such shifts necessarily explain the breadth of the current outbreak.
In Africa, most human cases of monkeypox have historically occurred through exposure to infected animals such as rodents and not through person-to-person transmission.
“What’s likely happened is an endemic infectious disease from Africa found its way into a social and sexual network and then was greatly aided by major amplification events like raves in Belgium to disseminate around the world,” Amesh Adalja, a senior scholar at the Johns Hopkins Centre for Health Security, said.
“Because it’s being transmitted through close contact in sexual encounters, many of the lesions are getting mistaken for other sexually transmitted infections, which may be delaying diagnosis.”
Increased vigilance by public health authorities, health care providers and individuals worldwide have dramatically improved detection in recent weeks.
“Whenever you start looking for a disease that’s new in a population, you find many, many more cases,” David Heymann, a professor at the London School of Hygiene and Tropical Medicine who formerly led the WHO’s Program on Emerging and other Communicable Diseases, told NBC News.
Heymann supported the theory that the disease may have been present in some populations for several years outside the 11 Central and West Africa countries where the virus has become endemic.
Cases may be circulating stealthily among people outside the global gay community, he suggested.
“The concern is looking in only one population rather than looking more broadly,” he said.