Screening for monkeypox virus infections in men who have sex with men in a sexual health clinic in Hanoi, Viet Nam

Before April 2022, monkeypox virus infection in humans was seldom reported outside African regions where it is endemic. Currently, cases are occurring worldwide. Transmission, risk factors, clinical presentation, and outcomes of infection are poorly defined.

Orthopoxvirus monkeypox (MPXV) forms two distinct clades: the MPXV Congo Basin clade viruses are endemic in the Congo Basin, human illness typically presents with symptoms similar to discrete, ordinary smallpox and has a case fatality rate of approximately 10% in unvaccinated populations; the MPXV West African clade viruses have been isolated in West Africa and appear to cause a less severe, and less inter-human transmissible disease. Recently, monkeypox outbreaks were reported in US and Sudan caused by MPXV West African and Congo Basin strains respectively. These events demonstrated the ability and trend of the virus to exploit new hosts and emerge globally; it also emphasizes the need for the diagnosis of MPXV, especially the ability to distinguish between Congo Basin and West African monkeypox strains. In this study, three new real-time PCR assays based on TaqMan probe technology were reported: the MPXV West African specific, Congo Basin strain specific and MPXV generic assays. The new assays demonstrated good specificity and sensitivity in the validation study with multiple platforms and various PCR reagent kits, and will improve the rapid detection and differentiation of monkeypox infections from other rash illness.

The magnitude of the 2022 multi-country monkeypox virus (MPXV) outbreak has surpassed any preceding outbreak. It is unclear whether asymptomatic or otherwise undiagnosed infections are fuelling this epidemic. In this study, we aimed to assess whether undiagnosed infections occurred among men attending a Belgian sexual health clinic in May 2022. We retrospectively screened 224 samples collected for gonorrhea and chlamydia testing using an MPXV PCR assay and identified MPXV-DNA-positive samples from four men. At the time of sampling, one man had a painful rash, and three men had reported no symptoms. Upon clinical examination 21–37 days later, these three men were free of clinical signs, and they reported not having experienced any symptoms. Serology confirmed MPXV exposure in all three men, and MPXV was cultured from two cases. These findings show that certain cases of monkeypox remain undiagnosed and suggest that testing and quarantining of individuals reporting symptoms may not suffice to contain the outbreak. Findings of unrecognized or asymptomatic monkeypox virus (MPXV) infections with replication-competent virus in humans suggest that a lack of recognized, clinical symptoms could play a role in virus transmission and the magnitude of the 2022 MPXV outbreak.