ITM finds key explanation for rapid spread of mpox virus

Researchers at the Institute of Tropical Medicine (ITM) in Antwerp provide evidence that infected persons may be able to transmit the mpox virus even before they have symptoms. This was revealed by samples from high-risk contacts and is an important explanation for the spread of the virus.

In Belgium and the rest of Europe, the mpox epidemic is waning. Since the first case in May, we already learned a lot about the virus and how it spreads. A few months ago, it emerged that the mpox virus can be contagious even without symptoms. Now scientists are showing that even in infected people, the potentially transmissible virus can be present even before the symptoms appear.

Close follow-up of high-risk contacts

The ITM study team investigated the risk of infection after high-risk contact. Twenty-five high-risk contacts such as sexual partners and roommates of infected persons took daily samples that were examined at ITM’s laboratory. Participants also kept a diary and were closely monitored by healthcare workers, with necessary advice and appropriate care.

Key explanation for spread

‘Laboratory results showed that participants were potentially infectious sometimes as early as four days before they showed symptoms,’ says Koen Vercauteren, clinical virologist at ITM. The results also teach us other things about the virus. First, the risk of infection through sexual contact is much higher than we have previously assumed. The risk of infection through non-sexual contact, on the other hand, is very low. Second, although skin lesions are a characteristic symptom, they are less common than we assumed. In the study, less than half of the infected participants showed typical symptoms, and only a third showed skin lesions.

Pre- and asymptomatic viral shedding in high-risk contacts of monkeypox cases: a prospective cohort study