Study finds three asymptomatic monkeypox cases

The monkeypox viral loads were similar immaterial of whether people showed symptoms or not

Monkeypox is transmitted by close contact with people who have symptomatic infection, and all those infected are assumed to show symptoms. But a recent study has found that people can be infected with monkeypox without showing any of the typical or atypical symptoms. The preprint has been posted in medrXiv server, which is yet to be peer-reviewed.

The study found three men tested positive for monkeypox but have no symptoms whatsoever. “All three men denied having had any symptoms in the weeks before and after the sample was taken. None of them reported exposure to a diagnosed monkeypox case, nor did any of their contacts develop clinical monkeypox,” the preprint notes. 

Similar to smallpox, everyone who is infected with monkeypox is expected to develop symptoms, and the virus is considered to spread through close contact with people who show symptoms. Since every individual infected with monkeypox is assumed to develop symptoms, and since close contact is most often needed for the virus to spread, it is considered that staying away from infected people and maintaining simple hygienic measures can halt the spread of monkeypox virus, as observed in several outbreaks in endemic regions.

But asymptomatic transmission can change and challenge the efforts to contain the monkeypox outbreak, which till July 4 has been reported in 6,027 people across 59 countries, including those in endemic countries in Africa.

According to the World Health Organization (WHO), the “extent to which asymptomatic infection may occur is unknown”. 

The researchers retrospectively screened 224 clinical samples collected for sexually transmitted infection (gonorrhea or chlamydia) throughout the month of May 2022 with a monkeypox-specific PCR. And they found evidence of asymptomatic monkeypox virus infection in three individuals. They tested anorectal and/or oropharyngeal samples collected from 224 people at the HIV/STI clinic of the Institute of Tropical Medicine in Antwerp, Belgium.

All the three men who tested positive for monkeypox were informed about their diagnosis and recalled to the clinic for additional case investigation and contact tracing. Follow-up samples were collected from all three men when they were recalled to the clinic. The repeat samples collected 21-27 days later were all negative.