A dozen men with no monkeypox symptoms tested positive for the virus, raising questions about asymptomatic spread

• A new study of 200 French men suggests some people can test positive for monkeypox without showing symptoms.
• It's still unclear whether asymptomatic transmission of monkeypox is possible, though.

A new study from France is raising fresh questions about whether monkeypox can be transmitted asymptomatically.

In the study, researchers collected anorectal swabs from 200 men who have sex with men — all who were getting routine STD testing — and tested them for monkeypox.

Critically, none of these men had any monkeypox symptoms when their tests were conducted, nor did they have any tell-tale early signs of infection — no lesions, no fever, no swollen lymph nodes, no nothing.

When their test results came back, the researchers were surprised to find that 13 of these 200 symptom-free men tested PCR positive for monkeypox.

That doesn't necessarily mean that those 13 men were capable of spreading monkeypox without knowing it, but it does raise the question: is asymptomatic transmission of monkeypox possible?

'Body weakness' as a potential early sign of monkeypox, before a rash emerges

The question of asymptomatic transmission during sex is also one that Dr. Dimie Ogoina — a Nigerian doctor who was one of the very first clinicians to raise the alarm about high numbers of young and active men contracting monkeypox back in 2017 — has been asking himself.

Ogoina, the medical director at Niger Delta University Teaching Hospital, told Insider that he recently saw a monkeypox patient in his clinic who said that "when they had a sexual relationship, there was no ulcer, no rash," and no fever, they only felt some "body weakness."

It was only "after the sexual relationship that he noticed a genital rash," Ogoina said. Then, "five days later, his sexual partner also noticed a genital rash."

Can monkeypox transmit via semen?

It's unclear whether monkeypox can be transmitted asymptomatically, perhaps via bodily fluids, and before people start feeling sick, but a few studies have already shown that the monkeypox virus can be detected in some infected people's semen.

"It's not necessarily unusual to see viral particles in body fluids — it doesn't mean that they are replication competent, able to cause disease," Ogoina added. "But I think it's also a signal that we need to deeply explore."

As is the case with COVID-19, a positive PCR test doesn't necessarily mean a person is infectious, either.

Dr. Lawrence Purpura, an infectious disease expert at Columbia University Irving Medical Center, studies how viruses transmit in semen. For some diseases (like Ebola) it's pretty clear that semen plays a role in transmission, while for others (like COVID) there's almost no evidence of that.

"Detecting monkeypox virus in semen is not entirely surprising," Purpura told Insider previously. "First you want to ask: is the detected virus viable and infectious?"

The "gold standard" for answering the question properly, he says, is "not just detect using PCR, but trying to grow the virus in a laboratory. And this is called virus isolation."

Asymptomatic spread, if it's happening, 'changes everything'

If it were the case that monkeypox can spread without symptoms, "it changes everything," Ogoina said.

The new French research, published Tuesday in the Annals of Internal Medicine, is still careful to emphasize that it's yet "unknown" whether monkeypox can transmit asymptomatically.

But the researchers also acknowledged that asymptomatic transmission would have huge implications for public health.

If monkeypox is spreading from some people without any symptoms, vaccinating only those who are exposed to a known case of monkeypox isn't enough to stop the outbreak.

After five years of sounding the alarm on monkeypox, Ogoina is well aware that there are plenty of mysteries left to unravel about how this virus spreads.

"There are a lot of things that are still not known about monkeypox — the natural history is not well described, because, of course, it has been a neglected disease," he said. He's hopeful that with more of the world's attention — and resources — trained on the problem, better answers will surface.

"Since the global north is now having cases, I'm sure there will be investments in research," he added.

"If we're able to, for instance, show that viable viruses can be isolated from the semen and it lingers for a while, then it completely transforms the type of public advice that we need to give, and how we look at transmission."