Tuberculosis: Causes and Characteristics
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Questions and Answers

What are the two types of Mycobacterium tuberculosis?

Human type and bovine type

What is the structure of Mycobacterium tuberculosis?

A central core of protein (tuberculoprotein), a polysaccharide fraction, and a lipid capsule

What is the mechanism of granuloma formation in tuberculosis?

Tubercle bacilli enter macrophages, replicate, and then are presented to T cells, leading to a type IV hypersensitivity reaction and formation of granuloma

What is the role of T cells in tuberculosis?

<p>T cells differentiate to T-helper 1 cells, which activate macrophages to kill bacteria</p> Signup and view all the answers

What is caseation necrosis due to?

<p>Hypersensitivity reaction and endarteritis obliterans</p> Signup and view all the answers

What is the type of hypersensitivity reaction that occurs in tuberculosis?

<p>Type IV hypersensitivity reaction</p> Signup and view all the answers

What are the two types of tissue reactions to tuberculosis?

<p>Cellular reaction (tubercle formation) and exudative reaction</p> Signup and view all the answers

What is the effect of pasteurization on Mycobacterium tuberculosis?

<p>Mycobacterium tuberculosis can be killed by pasteurization</p> Signup and view all the answers

What type of organs are affected in exudative tissue reactions?

<p>Serous sacs, lungs</p> Signup and view all the answers

What is a characteristic feature of a microscopic picture of a high immunity response to TB?

<p>Many granulomata, many epithelioid cells, many giant cells, few lymphocytes, and less caseation</p> Signup and view all the answers

What is the outcome of a primary pulmonary TB infection when the bacteria are not fully eliminated?

<p>Latent infection</p> Signup and view all the answers

What is the term for the spread of TB to many organs through the bloodstream?

<p>Miliary tuberculosis</p> Signup and view all the answers

What is the name of the complex that forms in the lungs as a result of primary pulmonary TB?

<p>Ghon’s complex</p> Signup and view all the answers

What is the term for the reactivation of TB due to lowered immunity?

<p>Secondary pulmonary tuberculosis</p> Signup and view all the answers

What are some conditions that can lead to reactivation of TB due to lowered immunity?

<p>AIDS, debilitating diseases, immunosuppressant drugs, and Hodgkin’s lymphoma</p> Signup and view all the answers

What is the term for the spread of TB to a single organ through the bloodstream?

<p>Isolated organ tuberculosis</p> Signup and view all the answers

What is the primary location of Ghon's focus in the lungs?

<p>Lower part of upper lobe or upper part of lower lobe</p> Signup and view all the answers

What is the difference between primary and secondary TB in terms of age of exposure and infection?

<p>Primary TB usually occurs in children, while secondary TB occurs in adults, often due to re-infection or re-activation.</p> Signup and view all the answers

What is the characteristic tissue reaction in secondary TB?

<p>Accelerated tissue reaction</p> Signup and view all the answers

What is the most accurate test for diagnosing tuberculosis?

<p>Identification of TB bacilli through sputum culture or PCR</p> Signup and view all the answers

What is the typical outcome of primary TB in patients with low immunity?

<p>Acute bronchopneumonia</p> Signup and view all the answers

What is the characteristic feature of Ghon's complex?

<p>Coalescent caseating tubercles</p> Signup and view all the answers

What is the difference between lymphadenitis in primary and secondary TB?

<p>Prominent lymphadenitis in primary TB, minimal lymphadenitis in secondary TB</p> Signup and view all the answers

What is the outcome of secondary TB in patients with high immunity?

<p>Chronic fibrocaseous pulmonary TB</p> Signup and view all the answers

Study Notes

Tuberculosis

  • Chronic, infective, granulomatous inflammation caused by tubercle bacilli
  • Aetiology:
    • Predisposing factors: low standard of nutrition and housing, low natural resistance
    • Pathogenic organism: Mycobacterium tuberculosis bacilli
  • Characteristics of Mycobacterium tuberculosis:
    • Aerobic, non-motile organism that can be killed by pasteurization
    • Weak gram-positive, stained with Ziehl-Neelsen stain
    • Structure: central core of protein (tuberculoprotein), polysaccharide fraction, lipid capsule

Methods of Infection

  • Infection occurs through contact with infected individuals or contaminated milk and dairy products

Pathogenesis of Granuloma Formation

  • Within 3 weeks of exposure, tubercle bacilli enter macrophages, replicate within phagosomes, and cause bacteremia and seeding of multiple sites
  • After 3 weeks, tubercle bacilli are drained to lymph nodes, presented to T cells, and activate macrophages to kill bacteria
  • Type IV hypersensitivity reaction develops, leading to granuloma formation and caseous necrosis

Morphology of TB Lesions

  • Tissue reaction to tuberculosis:
    • Cellular reaction (tubercle formation)
    • Exudative reaction
  • Characteristics of TB granuloma:
    • Many granulomata, epithelioid cells, giant cells, and few lymphocytes
    • Caseation necrosis due to hypersensitivity reaction and endarteritis obliterans

Fate of the Tubercle

  • Small lesions: replaced by fibrosis, bacteria may remain as latent infection
  • Large caseous lesions: reactivate, leading to secondary pulmonary tuberculosis, especially in individuals with lowered immunity (e.g., AIDS, debilitating disease, immunosuppressant drugs)

Primary Pulmonary Tuberculosis

  • Mode of transmission: inhalation of infected droplets
  • Primary pulmonary complex (Ghon's complex):
    • Ghon's focus: small area (1 cm), subpleural, lower part of upper lobe or upper part of lower lobe
    • Lymphangitis and lymphadenitis

Secondary Pulmonary Tuberculosis

  • Etiology:
    • Reactivation of latent infection
    • Re-infection
  • Pathogenesis:
    • Preexisting hypersensitivity induces rapid tissue response, leading to rapid localization of disease with less lymph node involvement
    • Marked caseation and destruction lead to cavitations and dissemination of infection

Diagnosis of Tuberculosis

  • History of contact with tuberculous patient
  • Toxic manifestations
  • Productive cough, pleuritic pain, hemoptysis
  • Tuberculin test
  • Biopsy: characteristic granuloma
  • Identification of TB bacilli (sputum culture, PCR): most accurate test for diagnosis

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Description

Learn about the causes and characteristics of tuberculosis, a chronic infective granulomatous inflammation caused by Mycobacterium tuberculosis bacilli. Understand predisposing factors, pathogenic organisms, and types of tuberculosis.

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