International researchers have warned that the ongoing mpox outbreak in the Democratic Republic of the Congo (DRC) has the potential to spread across borders more rapidly. The mpox virus has mutated, and the new variant, clade 1b, has become more infectious.
Genetic analyses of clade 1b, first detected in September 2023 in Kamituga, DRC, show that this variant has since undergone mutations making it more easily transmissible between humans. Scientists have identified three new subvariants, one of which has spread beyond Kamituga to other cities in the DRC, neighbouring countries, and even internationally (including to Sweden and Thailand). The new data may also suggest that clade 1b entails a high risk of miscarriage.
This new research has been published as an accelerated scientific publication in the esteemed journal Nature Medicine.
Originally, mpox was considered a zoonotic disease that primarily spread from animals to humans. However, in 2022, the world witnessed an outbreak primarily affecting men who have sex with men. The new clade 1b differs as both men and women are now contracting the virus. Additionally, an increasing number of infections are being reported among healthcare workers and children.
“It's somewhat like SARS-CoV-2 – the virus undergoes mutations as it spreads. For clade 1b, we see that one particular subvariant appears to have become better at transmitting between humans, and it has now been detected in several countries outside East Africa. In addition, the number of infected pregnant women who miscarry is high among those we have tested,” says Professor Frank Møller Aarestrup from DTU National Food Institute, who leads the GREAT-LIFE project. The GREAT-LIFE project is behind both the discovery of clade 1b and the development of a new PCR test, which enables the detection of clade 1b - undetectable by the original mpox tests.
This research indicates that the new variant is spreading rapidly, primarily through heterosexual contact in densely populated areas. “At present, we are seeing uncontrolled transmission of clade 1b in eastern DRC and Burundi, but to a lesser extent in other parts of East Africa. While there is some international spread, we do not yet expect a large outbreak outside the epicentre in East Africa. However, this situation demands immediate attention. It is crucial to avoid close contact, particularly sexual contact, in high-risk areas,” says Frank Aarestrup. The spread to neighbouring countries underscores the need for expanded cross-border cooperation to track disease transmission, treat patients, and disseminate health education, particularly among sex workers.
DTU National Food Institute coordinates the GREAT-LIFE project, which aims to build capacity for detecting disease outbreaks in East Africa. The project focuses on local implementation of PCR testing for viral diseases using portable equipment. This capacity-building initiative was rapidly tested when, by coincidence, the project launched alongside the emergence of the new clade 1b variant in the DRC.
The mpox outbreak meant that local researchers and healthcare personnel immediately needed the expertise and tools provided by the project. Led by Professor Frank Aarestrup, DTU National Food Institute’s contribution is to equip local researchers with the ability to conduct rapid research and deliver relevant results.
As part of its capacity-building efforts, the GREAT-LIFE project has: identified the new variant of the mpox virus; developed a PCR test to detect clade 1b; tracked and investigated its spread to Burundi; and examined the spread in and beyond Kamituga, DRC, as detailed in this article.
- Masirika LM, Udahemuka JC, Schuele L, et al. Epidemiological and genomic evolution of the ongoing outbreak of clade Ib mpox virus in the eastern Democratic Republic of the Congo. Nat Med. Published online February 11, 2025. doi:10.1038/s41591-025-03582-1