Some scientists speculate that the monkeypox virus, which has now been diagnosed in hundreds of people in 26 countries, may have been circulating quietly for years before suddenly appearing around the world.
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 does not normally spread easily from person to person has had such dramatic and troubling past appearances Month. “There may have been some undetected transmission for a time,” said Dr. Rosamund Lewis, the World Health Organization’s chief technical officer for monkeypox, during a briefing on Wednesday. “What we don’t know is how long this has been going on. I don’t know if it’s weeks, months or possibly a few years.”
At the University of Leuven in Belgium, virology professor Marc Van Ranst told NBC News that his lab’s sequencing revealed genetic mutations in the virus that were “limited” and that “none of them are smoking guns.
“Everyone is interested in more complete genomes to get an idea of a pretty important question: How long have these viruses been floating around under the radar?” said van Ranst. “I don’t think anyone believes that jumped out of Africa a few weeks ago.”
Scientists from the University of Edinburgh recently sequenced samples from the eruption and published their findings on May 30. The samples they examined were derived from a version of monkeypox identified in Singapore, Israel, Nigeria and the United Kingdom between 2017 and 2019.
While investigators have identified an “unexpectedly large number” of changes to the virus’ genetic code since that time, some experts don’t believe such shifts necessarily explain the breadth of the current outbreak.
In Africa, most human cases of monkeypox have historically occurred through contact with infected animals such as rodents, rather than human-to-human transmission.
“What probably happened is that an endemic infectious disease from Africa found its way into a social and sexual network and then was heavily assisted by big amplification events like raves in Belgium to spread around the world,” Dr. Amesh A. Adalja, a senior scientist at the Johns Hopkins Center for Health Security, said.
“And then,” Adalja added, “because it’s transmitted through close contact during sexual encounters, many of the lesions are mistaken for other sexually transmitted infections, which can delay diagnosis.”
Increased vigilance from health authorities, healthcare providers and individuals worldwide has dramatically improved detection in recent weeks.
“Anytime you start looking for a disease that’s new in a population, you find many, many more cases,” said Dr. David Heymann, a professor at the London School of Hygiene and Tropical Medicine who used to lead the WHO program on emerging and other communicable diseases, told NBC News.
Heymann supported the theory that the disease may have been present for several years in some populations outside of the 11 central and west African countries where the virus has become endemic. Cases could be secretly circulating among people outside the global gay community, he suggested.
“The concern is looking at just one demographic rather than looking broader,” he said.
Very mild monkeypox symptoms
The infection, which can cause painful lesions all over the body that leave permanent scars, usually goes away in a person in about three weeks. Most of the identified cases in Europe and the US have been mild — some so uncharacteristically subtle that they have been mistaken for other sexually transmitted infections — and have occurred in gay, bisexual, and other men who have sex with men. However, experts emphasize that close physical contact during sexual activity is the key factor in transmission.
Contrary to what is usually seen with monkeypox cases in Africa, some recent infections have resulted in “very, very mild” symptoms, possibly affecting just a single lesion, said Dr. Sébastien Poulin, an infectious disease specialist at St. Jérome Hospital in Montréal who diagnosed one of the first Canadian outbreak cases, NBC News said. “Doctors need to be aware of that.”
Additionally, monkeypox disease usually begins with a fever, but some recent U.S. cases have not reported a fever or other early signs before the lesions appear, according to the Centers for Disease Control and Prevention.
“Because of this, cases could be confused with more common infections like varicella zoster or sexually transmitted infections,” like genital herpes or syphilis, reported a CDC study released Friday.
According to the World Health Organization, 66 people died from the infection in African countries in 2022. Nigeria has been battling its own monkeypox outbreak since 2017 — one that may have served as an incubator for it to spread worldwide.
There have been no fatalities in the current outbreak in Europe or the US, although at least one person has been hospitalized in the US to treat severe pain from anal lesions, Capt. Jennifer McQuiston, associate director of the CDC’s High Consequence Pathogens and Division of Pathology, said during a Friday briefing.
McQuiston acknowledged the possibility that monkeypox virus cases had previously been missed in the US, but “not to any great extent,” she said during the briefing. In 2021, two cases were detected in the US – an individual in Texas in July and a separate case in Maryland in November. Both had recently traveled to Nigeria.
Van Ranst said the coming days of the outbreak are crucial in controlling the disease. According to WHO, as of June 1, there were 643 confirmed cases. If the cumulative case count by next week follows an exponential curve and maybe hits 4,000, “then this is not under control,” he said.
If instead the number only increases to about 1,000, the outbreak is likely only spreading in a linear fashion, which bodes well for global control of the virus, Van Ranst said.