Mpox Clade Ib Outbreak in DRC

February 17, 2025

The mpox clade Ib outbreak in the Democratic Republic of the Congo (DRC) has raised public health concerns since its emergence in September 2023. Recent genomic and epidemiological studies indicate that this outbreak is primarily linked to sexual activity among professional sex workers in densely populated urban areas. As of January 2025, over 9,500 laboratory-confirmed cases have been reported, with a case fatality rate of 3.4%.

Mpox Variants

There are two main types (clades) of mpox: Clade 1 and Clade 2. Each clade has subtypes that differ in transmission and severity.

Clade 2b (Global Outbreak, 2022-Present):

Caused a major outbreak in 2022, spreading globally.
Over 100,000 cases reported worldwide.
Low fatality rate in Europe (4 deaths per 10,000 cases).
Primarily affected gay & bisexual men and other men who have sex with men in the UK.

Clade 1a (Endemic in the DRC):

Found in the Democratic Republic of the Congo (DRC) for years.
Spread through contact with animals or their meat.
More deadly than Clade 2, especially among children.
Transmits within households and healthcare settings.

Clade 1b (New Deadlier Strain, 2023):

More transmissible and has a higher fatality rate.
Spreads within sexual networks and among close contacts.
Originated in DRC and has spread to neighboring countries.
UK detected an imported case on October 30, 2024, from affected regions.

Epidemiological Overview

The mpox clade Ib outbreak began in South Kivu, where 670 cases were documented from September 2023 to June 2024. The majority of cases were in females, comprising 52.4% of hospital admissions. In contrast, only 15.5% of suspected cases involved children under 16 years. This demographic shift marks the outbreak’s unique characteristics compared to previous incidents in the DRC.

Transmission Dynamics

The study conducted revealed that 83.4% of hospitalised cases reported recent sexual contact. Most of these interactions occurred in bars, suggesting that social venues play important role in the virus’s spread. The genomic analysis indicates multiple ongoing transmission chains, underscoring the complexity of the outbreak.

Clinical Manifestations

Among the hospitalised patients, there were seven reported deaths, predominantly among young adults aged 20-30 years. The presence of mpox lesions was noted in one foetus, indicating potential vertical transmission. Furthermore, 14 pregnant women were hospitalised, with a high rate of miscarriage observed.

Genomic

The genomic sequencing of 58 mpox genomes revealed various clusters and sub-clusters of the virus. The presence of APOBEC3 mutations suggests ongoing human-to-human transmission. These findings indicate that the outbreak is not a singular event but rather a series of interconnected incidents with diverse origins.

Public Health Implications

The rapid spread of mpox clade Ib necessitates urgent public health interventions. Enhanced surveillance, targeted health education, and support for affected communities are crucial. The data emphasises the need for a comprehensive approach to manage and contain the outbreak effectively.

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