Name: tb spread, latency, and reactivation
Uploaded: 2026-05-20T14:05:08.156Z
Duration: 1 min 23 s
Channel: JoVE

Tuberculosis is a chronic respiratory infection caused by Mycobacterium tuberculosis and spread through airborne droplet nuclei that carry the pathogen.In the lungs, alveolar macrophages engulf the bacteria but can not destroy them.The infected macrophages cross the alveolar epithelium, carrying the bacteria to the lung tissue.As the bacteria multiply inside the macrophages, some of the macrophages die, releasing the bacteria into the lung tissue.This causes an inflammatory response, drawing immune cells to the infection site.Over time, these immune cells surround the infected area, creating a tight cluster called a granuloma that walls off the bacteria to contain the infection.Inside the granuloma, most bacteria remain dormant. As a result, the host enters a clinically asymptomatic, noninfectious latent state.If immunity is weakened by factors such as malnutrition or aging, these granulomas can break down and release the bacteria.The bacteria then rapidly multiply in the lung tissue, causing inflammation and active symptomatic tuberculosis.

tuberculosis

Tuberculosis

Tuberculosis (TB) remains a significant global health concern, primarily targeting the lungs and spreading through airborne transmission. Infection begins when aerosolized droplet nuclei, expelled by an individual with active TB, are inhaled by another person. These microscopic particles carry Mycobacterium tuberculosis, the causative agent of TB. Upon reaching the alveoli, the bacilli are engulfed by alveolar macrophages. However, due to their specialized lipid-rich cell wall, these pathogens resist destruction and survive within the phagocytes.Intracellular Survival and DisseminationFollowing phagocytosis, infected macrophages traverse the alveolar epithelium, disseminating M. tuberculosis into the surrounding lung tissue and regional lymph nodes. The persistence of the bacteria is primarily attributed to the presence of cord factor (trehalose 6,6&#x2019;-dimycolate), a glycolipid on the bacterial cell wall. This virulence factor induces the formation of serpentine cords by promoting bacterial aggregation, thereby evading effective immune clearance. These cords are inefficiently phagocytosed by interstitial macrophages, leading to the recruitment of additional immune cells, including lymphocytes, to the site of infection.Granuloma Formation and LatencyThe host immune response culminates in the formation of granulomas&#x2014;organized structures composed of macrophages, epithelioid cells, and T lymphocytes that encase the infected cells. Within these granulomas, the bacteria can remain viable yet dormant for extended periods, establishing latent TB. This phase is clinically asymptomatic and non-contagious but poses a risk for future reactivation.Reactivation and TransmissionReactivation of latent tuberculosis can happen under immunocompromising conditions such as malnutrition, advanced age, or co-infection with HIV. In older individuals, reduced T-cell production due to thymic shrinkage weakens immune defense. In malnourished individuals, a low white blood cell count further reduces the body&#x2019;s ability to control infection. Because of this, the immune system may no longer maintain the integrity of granulomas, allowing Mycobacterium tuberculosis to escape into the pulmonary environment and multiply rapidly. This leads to active tuberculosis, marked by inflammation, tissue damage, and symptoms such as a persistent cough. Coughing releases infectious droplets into the air, helping the disease spread easily.

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tb spread, latency, and reactivation

Tuberculosis is a lung infection caused by Mycobacterium tuberculosis, and it spreads through the air. When a person with active TB coughs or breathes out, tiny droplet nuclei can be inhaled by someone else. These particles reach the alveoli, the small air sacs in the lungs, where the bacteria are taken up by alveolar macrophages, a type of immune cell.

Mycobacterium tuberculosis can survive inside these phagocytes because of its lipid-rich cell wall. After phagocytosis, infected macrophages move through the alveolar epithelium and carry the bacteria into nearby lung tissue and regional lymph nodes. A key virulence factor called cord factor, or trehalose 6,6'-dimycolate, helps the bacteria clump into serpentine cords. These cords are not cleared well by interstitial macrophages, so more immune cells, including lymphocytes, are recruited to the infection site.

The immune response can build granulomas around the infected cells. Granulomas are organized clusters of macrophages, epithelioid cells, and T lymphocytes. Inside these structures, the bacteria may stay alive but inactive for a long time. This stage is called latent TB. It does not usually cause symptoms and is not contagious, but it can become a problem later.

Latent tuberculosis can reactivate when the immune system is weakened. The transcript describes this in malnutrition, advanced age, and HIV co-infection. In older people, thymic shrinkage leads to reduced T-cell production. In malnourished people, a low white blood cell count weakens defense. If granulomas break down, Mycobacterium tuberculosis can escape into the lungs, multiply quickly, and cause active TB with inflammation, tissue damage, and a persistent cough. That cough can release infectious droplets into the air and spread the disease.

TB Spread, Latency, and Reactivation

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Tuberculosis is a lung infection caused by Mycobacterium tuberculosis, and it spreads through the air. When a person with active TB coughs or breathes out, tiny droplet nuclei can be inhaled by someone else. These particles reach the alveoli, the small air sacs in the lungs, where the bacteria are taken up by alveolar macrophages, a type of immune cell. Mycobacterium tuberculosis can survive inside these phagocytes because of its lipid-rich cell wall. After phagocytosis, infected macrophages...

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key terms and concepts

Follow how tuberculosis spreads through the lungs, forms granulomas, stays latent, and can reactivate when immunity weakens in high school biology.

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JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

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TB Spread, Latency, and Reactivation

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