China has confirmed its first human case of mpox virus (MPXV) clade Ib, marking a significant development in the global spread of this high-risk viral strain. Published in Nature Communications by Sun J, Zhou L, Wu B, et al., the study offers a comprehensive account of the case’s clinical, virological, and epidemiological features.
The infected patient, a 28-year-old woman from South Africa residing in China, developed a generalized rash and systemic symptoms following sexual contact with an asymptomatic male traveler from the Democratic Republic of the Congo (DRC). Genetic sequencing revealed that the virus — named MPXV ZJ-JX-2025 — closely matched circulating clade Ib strains from Central Africa, a variant known for higher mortality rates than the clade IIb strains responsible for previous outbreaks.
Clade Ib Reaches China: Key Findings
- The patient developed symptoms on December 21, 2024, beginning with fatigue and progressing to a widespread vesicular rash by Day 10.
- Skin lesion samples were 100% positive for MPXV DNA, with high viral loads persisting throughout illness.
- Urine samples remained positive up to Day 20, raising concerns over unrecognized transmission routes.
- Remarkably, no oral or genital lesions were observed — a contrast to most clade IIb cases.
Contact Tracing and Containment
Health authorities identified and monitored 211 close contacts, including 26 individuals at high or moderate risk. Despite environmental evidence of viral shedding from the male partner’s living spaces, no secondary infections were recorded, indicating limited transmission in non-sexual contexts.
Environmental samples from the partner’s home tested positive for MPXV DNA, supporting possible asymptomatic transmission and fomite-related risks, such as contaminated razors.
Genomic Insights Raise Global Surveillance Alarms
Whole-genome sequencing classified the strain within the clade Ib lineage, identifying 141 non-synonymous mutations, including 35 previously unrecorded in DRC-based strains. The closest known match was to a 2024 isolate from Brazzaville, Republic of the Congo, with 99.98% identity.
These findings underscore the evolutionary divergence and potential for wider dissemination of clade Ib through human mobility.
Implications for Public Health and Policy
Experts warn that this case reflects the growing international threat posed by clade Ib, especially given the absence of symptoms in the index patient’s contact. While the case in China was isolated, the study highlights key concerns:
- Asymptomatic and atypical presentations may complicate detection and control.
- Urine and environmental shedding suggest that current screening strategies may need expansion.
- Genomic surveillance at borders should be urgently strengthened.
The World Health Organization (WHO) declared mpox clade Ib a Public Health Emergency of International Concern (PHEIC) in August 2024 after its emergence in 12 non-endemic countries.
Conclusion
While this case was successfully contained, researchers emphasize the need for vigilant sexual network monitoring, fomite awareness, and rapid genomic response to prevent future transmission chains.
This case demonstrates how rapidly high-risk pathogens can cross borders and evade early detection
Dr. Guoqing Shi of the Zhejiang CDC
With the virus’s silent spread potential, public health officials are urged to adhere to WHO guidelines, including 21-day isolation for confirmed cases, and enhance international data sharing on mpox evolution.
Citation:
Sun J, Zhou L, Wu B, et al. First Confirmed Human Case of Mpox Virus Clade Ib in China: Epidemiological and Virological Characterization. Nature Communications. 2025;16:4888. doi:10.1038/s41467-025-4888-z
