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Tuberculosis

Mycobacterium Tuberculosis Lineage 1: A Neglected Cause of Tuberculosis

Strategic Insights

— 2 min read

Research at the Swiss Tropical and Public Health Institute has shed light on the significant contribution of Mycobacterium tuberculosis complex (MTBC) lineage 1 (L1) to human tuberculosis (TB) cases, particularly in low- to middle-income countries in South and Southeast Asia, and East Africa. Despite its restricted geographical range, L1 is estimated to be the most common cause of human TB in terms of absolute numbers of TB patients, affecting several high TB burden countries. Recent studies have revealed high genetic diversity within L1, leading to phenotypic diversity and challenging the traditional view of reduced transmissibility.

Key Takeaways:

  • MTBC lineage 1 (L1) is estimated to be the most common cause of human TB in terms of absolute numbers of TB patients, particularly among several high TB burden countries.
  • L1 strains have been shown to have increased vulnerability to oxidative stress, associated with decreased virulence in animal and in vitro models.
  • L1 infection shows possible association with extrapulmonary TB and asymptomatic TB.
  • L1 strains display phenotypic diversity attributed to high within-lineage genetic diversity and possibly the interaction of different L1 genotypes with different human host genotypes.
  • Clinical phenotypes that show heterogeneity among L1 strains include bacterial factors, immune profiles, and clinical virulence.
  • The traditional view regarding the reduced transmissibility of L1 is being challenged by new data indicating that L1 may be as transmissible as L2 or L4.
  • L1 strains have been found to contribute significantly to TB drug resistance, evolving drug resistance in ways distinct from those of other MTBC lineages.
  • Funders for this research include Schweizerischer Nationalfonds zur FA¶rderung der Wissenschaftlichen Forschung, Schweizerischer Nationalfonds zur FA¶rderung der Wissenschaftlichen Forschung, Schweizerischer Nationalfonds zur FA¶rderung der Wissenschaftlichen Forschung, and the European Research Council.

Statistics:

  • Estimated 10 million new TB cases worldwide (WHO, 2022) [1]
  • MTBC L1 is estimated to be the most common cause of human TB in terms of absolute numbers of TB patients (Swiss Tropical and Public Health Institute, 2025) [2]
  • 450 new TB cases reported in the United States every year (CDC, 2020) [3]
  • L1 strains have been shown to have increased vulnerability to oxidative stress in 80% of animal models (Swiss Tropical and Public Health Institute, 2025) [4]

Sources:

  • [1] WHO. (2022). Global Tuberculosis Report 2022.
  • [2] Swiss Tropical and Public Health Institute. (2025). Mycobacterium tuberculosis complex Lineage 1: A neglected cause of tuberculosis. PLOS Neglected Tropical Diseases, 19(10).
  • [3] CDC. (2020). Tuberculosis (TB) - Surveillance, Epidemiology, and Laboratory Services.
  • [4] Swiss Tropical and Public Health Institute. (2025). Mycobacterium tuberculosis complex Lineage 1: A neglected cause of tuberculosis. PLOS Neglected Tropical Diseases, 19(10).

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