WHO Confirms Two Cases of Recombinant Mpox Virus Strain
The World Health Organization (WHO) has confirmed two cases of a recombinant mpox virus (MPXV) strain, combining genomic elements of clades Ib and IIb. One case was identified in the United Kingdom and another in India. Both patients reported recent travel and experienced mild illness, with no severe complications.
Contact tracing did not identify any secondary cases related to these detections.
Understanding Mpox and Recombination
Mpox is an infectious disease caused by the monkeypox virus (MPXV), which belongs to the Orthopoxvirus genus, the same family as the smallpox virus. It typically spreads through close physical contact, including sexual contact, and can also be transmitted via contaminated materials or respiratory droplets. Common symptoms include fever, swollen lymph nodes, and a rash or lesions.
Genetic recombination is a natural process that can occur when two related viruses simultaneously infect the same individual, leading to an exchange of genetic material and the potential formation of a new variant. Detailed genomic analysis indicated that the two confirmed cases, despite occurring weeks apart, involved the identical recombinant strain, suggesting the possibility of additional undetected cases.
Case Details
United Kingdom Case
Detected in December 2025 in a traveler returning from the Asia Pacific region. Initial laboratory tests suggested clade Ib, but whole-genome sequencing subsequently identified genetic regions from both clade Ib and clade IIb strains. Repeat sequencing confirmed these findings and indicated the virus's ability to replicate and potentially transmit.
India Case
A patient developed symptoms in September 2025 and was initially classified as infected with clade II MPXV. Following updates to global genomic databases, the virus was reclassified as the same recombinant strain found in the UK, making it the earliest known detection of this specific strain.
WHO's Assessment and Recommendations
The WHO stated that it is currently premature to draw conclusions regarding the transmissibility or clinical characteristics of mpox caused by recombinant strains, given the limited number of detected cases.
The clinical presentations observed in both patients were consistent with known mpox infections.
Overall Risk Assessment
The overall risk assessment from WHO remains unchanged:
- Moderate risk: For men who have sex with men with new or multiple partners, sex workers, and individuals with multiple casual sexual partners.
- Low risk: For the general population without specific risk factors.
WHO emphasized that standard clade differentiation PCR tests might not reliably identify recombinant MPXV strains, underscoring the necessity of genomic sequencing for accurate detection. The organization urged all countries to:
- Remain vigilant for MPXV genetic recombination.
- Maintain epidemiological surveillance.
- Continue sequencing efforts.
- Implement vaccination programs for at-risk groups.
- Uphold effective infection prevention and control measures.
Based on the current information, no travel or trade restrictions are recommended by the WHO.