3.7
Tuberculose pulmonaire II : Physiopathologie
La tuberculose, ou TB, est une maladie infectieuse bactérienne causée par Mycobacterium tuberculosis. Bien que son impact principal soit sur les poumo…
La physiopathologie de la tuberculose commence lorsqu’un hôte sensible inhale des gouttelettes aérosolisées contenant Mycobacterium tuberculosis.
Les gouttelettes atteignent les alvéoles des poumons, où les bactéries se multiplient et rencontrent les macrophages alvéolaires, qui les engloutissent.
Cependant, au lieu de détruire les bactéries, les macrophages leur permettent de survivre et de se répliquer à l’intérieur.
Après 2 à 6 semaines, le corps initie une réponse immunitaire à médiation cellulaire, formant une structure spécialisée appelée granulome pour contenir la propagation bactérienne.
Le granulome comprend des cellules immunitaires, des cellules bactériennes vivantes et mortes, des cellules T et des macrophages.
La bactérie peut rester dormante dans le granulome, ne causant aucun symptôme et n’étant pas contagieuse. Ce stade est connu sous le nom d’infection tuberculeuse latente.
Si le système immunitaire est compromis, la tuberculose latente peut évoluer vers une tuberculose active par le processus de caséation, où le centre d’un granulome se nécrose, formant une substance semblable à du fromage appelée caséum.
Cette matière caséeuse s’érode ensuite en bronche, créant une cavité qui facilite la prolifération bactérienne rapide et la propagation potentielle de l’infection par le sang ou la lymphe.
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Q1: How does Mycobacterium tuberculosis survive inside alveolar macrophages?
When susceptible hosts inhale aerosolized droplets containing Mycobacterium tuberculosis, the bacteria reach the lungs' alveoli where alveolar macrophages engulf them. However, instead of destroying the bacteria, the macrophages allow them to survive and replicate within. This intracellular survival mechanism enables the infection to establish and persist in the host.
Q2: What is a granuloma and why does the body form one?
A granuloma is a specialized immune structure that forms 2-6 weeks after infection when the body initiates a cell-mediated immune response. It comprises immune cells, live and dead bacterial cells, T-cells, and macrophages clustered together. The granuloma's primary function is to contain and prevent the spread of Mycobacterium tuberculosis throughout the body.
Q3: What is the difference between latent and active tuberculosis infection?
In latent tuberculosis infection, bacteria remain dormant within the granuloma, causing no symptoms and being non-contagious. Active tuberculosis disease develops when the immune system is compromised, allowing bacteria to multiply and spread, causing tissue damage and symptoms. About 5-10% of individuals with latent TB infection progress to active disease, particularly if their immune system becomes weakened.
Q4: How does caseation lead to cavity formation in tuberculosis?
Caseation occurs when the center of a granuloma becomes necrotized, forming a cheese-like substance called caseum. If this caseous material erodes into a bronchus, it creates a cavity that facilitates rapid bacterial proliferation. This cavitation process worsens symptoms and increases the potential for bacterial spread through blood or lymph.
Q5: How is tuberculosis transmitted from one person to another?
Tuberculosis transmission begins when a person inhales droplet nuclei containing Mycobacterium tuberculosis. These droplets are typically released into the air when an individual with pulmonary or laryngeal TB coughs, sneezes, or speaks. The inhaled bacteria then reach the alveoli in the lungs, where the infection cycle begins.
Q6: What role does the cell-mediated immune response play in tuberculosis infection?
Approximately 2-6 weeks post-infection, the body mounts a cell-mediated immune response where T cells recognize mycobacterial antigens presented by infected macrophages. This triggers cytokine release, activating other immune cells and processes that lead to granuloma formation. This immune response aims to contain bacterial spread and is essential for controlling the infection.
Q7: Can tuberculosis spread to organs outside the lungs?
Yes, from the lungs, Mycobacterium tuberculosis can spread through the bloodstream, causing miliary TB, or through the lymphatic system to other organs, resulting in extrapulmonary tuberculosis. This dissemination occurs when bacteria escape the primary infection site and establish secondary infections in various body systems, complicating the disease presentation and nursing management and prevention strategies.