Mpox Caused by Clade Ib: Epidemiological Characteristics, Prevention, and Control
The global mpox (formerly monkeypox) outbreak, which emerged in 2022, has evolved into a persistent public health challenge. Initially concentrated among men who have sex with men (MSM) through human-to-human transmission of Clade IIb, the epidemic has recently shifted with the emergence of Clade Ib, a sublineage of Clade I (historically associated with Central Africa). This new variant has raised alarms due to its increased transmissibility, higher case fatality rate (CFR), and potential for broader demographic impact. Understanding the epidemiological trends, risks posed by Clade Ib, and strategies for prevention and control is critical to mitigating its spread.
Epidemiological Trends of Mpox
Since the first case outside Africa was reported in the United Kingdom in May 2022, mpox has spread to nearly all World Health Organization (WHO) regions. By September 30, 2024, 109,699 laboratory-confirmed cases were reported globally. The Americas accounted for the majority (65,877 cases), followed by Europe (28,176), Africa (9,425), the Western Pacific (4,379), Southeast Asia (971), and the Eastern Mediterranean (871). While cases in non-African regions peaked in mid-2022 to late 2023, Africa experienced a dramatic surge in 2024, with 10,944 confirmed cases (78% occurring in 2024) and 33 deaths. The Democratic Republic of the Congo (DRC) alone reported 8,207 cases (6962 in 2024), highlighting Clade Ib’s rapid spread.
Historically, mpox cases outside Africa were dominated by Clade IIb, characterized by low CFR (0.1–0.2%) and transmission primarily through sexual contact among MSM. However, Clade Ib, first detected in the DRC in 2023, has shown distinct characteristics:
- Higher CFR: Clade Ib’s CFR is approximately 10%, significantly higher than Clade IIb. Deaths are concentrated in children under 15 years (78% of fatalities), including stillbirths.
- Expanded Transmission Routes: While Clade IIb spreads via close physical or sexual contact, Clade Ib demonstrates potential for household transmission and respiratory droplet spread. Thailand reported the first Asian Clade Ib case via droplet transmission in August 2024.
- Demographic Shift: Unlike Clade IIb’s focus on MSM, Clade Ib affects broader populations, including women and children. Children under 10 years face near-100% CFR during outbreaks, a stark contrast to the low mortality observed in adults with residual smallpox immunity.
The Threat of Clade Ib
Clade Ib’s emergence represents a significant escalation in mpox’s global threat. Genetic analysis reveals it diverged from Clade I (Central African clade) and carries mutations linked to enhanced human adaptation. Key concerns include:
- Severity and Clinical Outcomes: Clade Ib infections are associated with severe complications such as myocarditis and adverse pregnancy outcomes. Hospitalization rates among children under 4 years are 112% higher than in adults aged 15–44.
- Global Spread Potential: Clade Ib has already spread beyond the DRC to neighboring African countries, with cases detected in Sweden and Thailand. Its ability to transmit via droplets and indirect contact (e.g., contaminated clothing) increases the risk of international dissemination.
- Diagnostic and Surveillance Challenges: Current diagnostic tools, optimized for Clade II, may lack sensitivity for Clade Ib. Environmental surveillance methods, such as wastewater monitoring, are being explored to track viral presence, building on strategies used during the COVID-19 pandemic.
Prevention and Control Strategies
Addressing the Clade Ib outbreak requires a multi-faceted approach integrating surveillance, vaccination, public health education, and international collaboration.
1. Enhanced Surveillance and Case Management
- Real-Time Monitoring: Strengthening laboratory capacity and genomic sequencing is essential to identify Clade Ib and track mutations. The WHO has approved emergency use of in vitro diagnostics for mpox, but Clade Ib-specific assays are urgently needed.
- Hospital Preparedness: Hospitals must adopt protocols for isolating suspected cases, managing severe outcomes (e.g., myocarditis), and preventing nosocomial transmission. The WHO’s 2022 guidelines on clinical management and infection control remain foundational but require updates to address Clade Ib’s unique risks.
- Wastewater Surveillance: Piloted in the U.S., wastewater testing offers a non-invasive method to detect mpox in communities, enabling early outbreak responses.
2. Vaccination Strategies
Vaccination remains the cornerstone of mpox prevention. While smallpox vaccines (e.g., ACAM2000) provide ~85% cross-protection, newer vaccines like MVA-BN (Modified Vaccinia Ankara-Bavarian Nordic) are prioritized for their safety profile. In September 2024, the WHO granted emergency authorization for MVA-BN, though its use in children under 18 remains off-label. Challenges include:
- Equitable Access: Low-income countries, particularly in Africa, face vaccine shortages. Global partnerships must prioritize dose allocation to high-risk regions.
- Booster Doses: Long-term immunity data are lacking. Studies are ongoing to determine if booster doses are necessary to sustain protection.
3. Public Health Education and Community Engagement
- Risk Communication: Messaging should target high-risk groups (e.g., travelers to endemic regions) and emphasize avoiding close contact with symptomatic individuals. Households with confirmed cases must disinfect contaminated surfaces and isolate infected members to protect children.
- Sexual Health Advocacy: MSM communities, still at risk for Clade IIb, require continued education on safe practices. However, campaigns must adapt to address Clade Ib’s broader transmission routes.
4. International Collaboration
The WHO’s 2024 declaration of mpox as a Public Health Emergency of International Concern (PHEIC) underscores the need for coordinated action. Key priorities include:
- Data Sharing: Open platforms for sharing genomic, clinical, and epidemiological data can accelerate research on Clade Ib’s behavior and vaccine efficacy.
- Resource Mobilization: Funding is critical to scale up diagnostics, vaccines, and treatments in resource-limited settings. The Strategic Framework for Enhancing Prevention and Control of Mpox 2024–2027 outlines targets for outbreak containment but requires robust financial and political support.
Conclusion
The emergence of Clade Ib mpox represents a pivotal moment in the evolution of this disease. Its high CFR, expanded transmission routes, and impact on vulnerable populations like children necessitate urgent, globally coordinated responses. While advancements in surveillance and vaccination offer hope, gaps in equity, diagnostics, and long-term immunity persist. Success hinges on integrating scientific innovation with grassroots public health efforts, ensuring that lessons from past outbreaks inform a proactive defense against this escalating threat.
doi.org/10.1097/CM9.0000000000003464
Was this helpful?
0 / 0