Tuberculosis

Abstract

Tuberculosis (TB) is a major health threat caused by the intracellular bacterial pathogen Mycobacterium tuberculosis (Mtb). Globally, 10 million individuals fell ill of TB and 1.4 million died in 2019. The COVID-19 pandemic has severely impacted on TB notifications in 2020, thereby markedly increasing morbidity and mortality caused by TB. The lung is the most frequent site of disease manifestation, the site of pathogen entry and the source of dissemination. In the infected lung, granulomas are formed at the site of Mtb persistence which primarily consist of macrophages of different maturation stages and T lymphocytes. Solid granulomas contain Mtb, thus preventing outbreak of active disease. The individual is now latently infected. Once Mtb evades immune control, granulomas become necrotic and later caseous. Active TB disease has started. Diagnosis of TB is done by chest X-ray, microscopy, bacterial culture, molecular test, and immunologic test. TB can be cured by a combination of 3-4 specific drugs given over a period of 6-9 months. Increasing incidences of multi-drug and extensively drug-resistant Mtb render therapy difficult to impossible. The current vaccine, Bacille Calmette-Guérin (BCG) prevents extrapulmonary childhood TB but fails to protect against pulmonary TB in all age groups. New vaccines against TB are urgently needed. New candidates that have entered clinical trials are killed whole cell vaccines, recombinant live vaccines, Mtb antigen-adjuvant formulations or viral vectors expressing Mtb antigens.