Changing Mycobacterium tuberculosis population highlights clade-specific pathogenic characteristics

Area of Science:

• Microbiology
• Epidemiology
• Evolutionary Biology

Background:

• Mycobacterium tuberculosis strains are classified into major clades based on evolutionary markers.
• These clades may possess distinct properties influencing local population structures and disease dynamics.

Purpose of the Study:

• To analyze the incidence of tuberculosis (TB) caused by predominant clades (Beijing, Haarlem, LAM, Quebec, Low-Copy Clade) in Cape Town over 12 years.
• To investigate if different clades exhibit varying epidemiological characteristics and clinical outcomes.

Main Methods:

• Retrospective analysis of TB case incidence stratified by M. tuberculosis clade.
• Longitudinal study over a 12-year period in a Cape Town community.
• Comparison of drug-susceptible and drug-resistant strain dynamics across clades.

Main Results:

• The Beijing clade incidence increased exponentially (doubling time 4.86 years), while other clades remained stable.
• Beijing clade growth was solely due to drug-susceptible strains.
• Drug-susceptible Beijing cases showed higher sputum positivity and lower treatment success rates compared to non-Beijing cases.

Conclusions:

• The rapid emergence of Beijing strains indicates adaptation to the local environment and presents a major challenge for TB control.
• Enhanced pathogenicity, rather than transmissibility, is suggested as the driver for Beijing strain success.
• Targeted interventions may be necessary to address the growing burden of Beijing clade TB.