Health officials in the Republic of the Congo have confirmed the presence of a monkeypox virus lineage previously associated with West African outbreaks, marking a significant shift in the region’s epidemiological landscape. Researchers identified evidence of monkeypox virus clade IIb lineage A.2.2 in the country, where clade I viruses have historically been endemic.
The discovery, detailed in recent genomic surveillance data, highlights a complex scenario where three distinct viral clades—Ia, Ib, and IIb—are now co-circulating within the same population. This convergence raises concerns among public health experts regarding the potential for viral recombination and the need for enhanced diagnostic capabilities across Central Africa.
“The detection of clade IIb in this region highlights the growing complexity of MPXV epidemiology in a historically endemic region,” researchers noted in the study. The findings come as the World Health Organization and Africa Centers for Disease Control and Prevention continue to monitor a surge in cases driven largely by clade I variants in the neighboring Democratic Republic of the Congo (DRC).
A New Variant in Pointe-Noire
The identification of the new lineage centers on a specific case reported in Pointe-Noire, the economic capital of the Republic of the Congo. On March 22, 2025, a 43-year-old man presented at a private outpatient clinic with fever, fatigue, and a skin rash in the genital area.
Initially, physicians suspected syphilis, a common differential diagnosis for such symptoms. However, a closer physical examination revealed disseminated skin lesions, including vesicles and pustules on the limbs, trunk, back, and buttocks. Subsequent diagnostic tests for syphilis, HIV, and hepatitis were negative.
Samples were transferred to the National Public Health Laboratory in Brazzaville for molecular analysis. The patient, who reported recent travel to France and Ivory Coast, was isolated at home and treated with supportive care. He made a full recovery after 19 days, with no observed transmission to family members or healthcare workers.
Initial diagnostic results using GeneXpert technology returned positive for monkeypox virus clade II. Further genomic sequencing confirmed the virus as clade IIb, lineage A.2.2. This lineage has been linked to recent outbreaks in Sierra Leone and travel-related cases in Europe, the United States, and Australia.
Surveillance Data and Co-Circulation
The single case in Pointe-Noire is part of a broader surveillance effort conducted between January and August 2025. During this period, health authorities identified an additional 56 mpox cases across seven of the country’s 12 administrative departments.
The genomic breakdown of these cases reveals a diverse viral landscape:
- Clade Ib: 32 cases
- Clade Ia: 16 cases
- Clade IIb: 2 introductions (including the Pointe-Noire case)
Historically, the Republic of the Congo has seen outbreaks primarily driven by clade Ia, particularly in the northern regions. However, introductions of clade Ib linked to Kinshasa, DRC, were identified in the capital, Brazzaville, in 2024 and 2025. The addition of clade IIb suggests multiple introduction events and sustained human-to-human transmission.
Epidemiological data indicates that several lineages of clade Ia and Ib were co-circulating in major administrative and economic hubs, including Brazzaville and Pointe-Noire. This mixture of viral types in a confined geographic area increases the biological risk for recombination events, which could potentially result in new viral phenotypes with different transmission or severity characteristics.
Genomic Analysis and Origins
Whole-genome sequencing of the clade IIb specimen revealed a genome length of 197,200 base pairs. Phylogenetic analysis placed the sequence within lineage A.2.2, clustering with recent sequences from Togo, the United States, and Australia.
Researchers used a Bayesian Markov chain Monte Carlo approach to assess the evolutionary dynamics. The analysis estimated the time to the most recent common ancestor between the Republic of the Congo sequence and its closest relatives at mid-2023. This timing suggests a recent cross-border importation event rather than long-term, undetected local circulation.
Despite the clustering with international sequences, researchers caution that sparse sampling in the region hinders the precise reconstruction of transmission chains. The patient’s travel history to France and Ivory Coast suggests the infection may have been contracted while traveling in West Africa or Europe, mirroring patterns seen in the 2022 global outbreak.
Public Health Implications
The presence of multiple clades underscores the need for a regionally coordinated response. In August 2024, the Africa CDC listed mpox as a Public Health Emergency of Continental Security, followed by a World Health Organization declaration of a Public Health Emergency of International Concern.
In response to the findings in the Republic of the Congo, health authorities have implemented several control measures in Pointe-Noire:
- Strengthening local laboratory diagnostics using GeneXpert platforms.
- Enhancing molecular epidemiology surveillance through next-generation sequencing.
- Outreach to healthcare settings to improve clinical management and hygiene practices.
Experts emphasize that the ability to detect emerging pathogens is directly related to access to healthcare and diagnostic infrastructure. Large parts of the Republic of the Congo remain remote, necessitating increased surveillance in border regions shared with the DRC and the Central African Republic.
As surveillance continues, health officials are focusing on expanding access to decentralized diagnostics and vaccines. The co-circulation of clades Ia, Ib, and IIb serves as a reminder of the virus’s evolutionary capacity and the importance of maintaining robust genomic monitoring systems to track potential changes in transmission dynamics.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. For health concerns regarding mpox or other infectious diseases, please consult a qualified healthcare professional or refer to guidance from the World Health Organization or local health authorities.
Health authorities in the Republic of the Congo plan to continue genomic sequencing of suspected cases to clarify the evolutionary trajectory of the virus. The next phase of surveillance will focus on border regions to determine if further introductions of clade IIb have occurred and to monitor for any signs of viral recombination.
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