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Questions and Answers
Tuberculosis is caused by a virus.
Tuberculosis is caused by a virus.
False (B)
Bovine tuberculosis is typically acquired through the inhalation of infected droplets.
Bovine tuberculosis is typically acquired through the inhalation of infected droplets.
False (B)
Mycobacteria are slender anaerobic gram-negative rods.
Mycobacteria are slender anaerobic gram-negative rods.
False (B)
The Ziehl-Neelsen stain is employed to identify acid-fast bacteria such as mycobacteria.
The Ziehl-Neelsen stain is employed to identify acid-fast bacteria such as mycobacteria.
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Neutrophils are the first cells to be attracted to the site of tuberculosis infection and are very effective at destroying the bacteria.
Neutrophils are the first cells to be attracted to the site of tuberculosis infection and are very effective at destroying the bacteria.
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Langhans’ giant cells are formed by the fusion of fibroblasts.
Langhans’ giant cells are formed by the fusion of fibroblasts.
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Caseation necrosis refers to the hardening of tissue in a granuloma.
Caseation necrosis refers to the hardening of tissue in a granuloma.
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Transplacental transmission of TB is a frequent mode of infection.
Transplacental transmission of TB is a frequent mode of infection.
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A cold abscess results from decreased caseation within infected tissues.
A cold abscess results from decreased caseation within infected tissues.
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A sinus forms when a cold abscess extends and discharges caseous material onto the skin surface.
A sinus forms when a cold abscess extends and discharges caseous material onto the skin surface.
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Immunization against TB uses live, virulent strains of bovine TB bacilli.
Immunization against TB uses live, virulent strains of bovine TB bacilli.
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The Mantoux skin test utilizes purified protein derivative (PPD) to trigger a immediate hypersensitivity reaction.
The Mantoux skin test utilizes purified protein derivative (PPD) to trigger a immediate hypersensitivity reaction.
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A positive Mantoux test is characterized by an indurated area of at least 10 mm in diameter, peaking at 24-48 hours.
A positive Mantoux test is characterized by an indurated area of at least 10 mm in diameter, peaking at 24-48 hours.
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Tuberculosis can spread locally via macrophages carrying the bacilli.
Tuberculosis can spread locally via macrophages carrying the bacilli.
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Transbronchial spread of tuberculosis involves dissemination from the renal system into the ureter.
Transbronchial spread of tuberculosis involves dissemination from the renal system into the ureter.
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Reactivation tuberculosis is always an exogenous infection in non immunized individuals.
Reactivation tuberculosis is always an exogenous infection in non immunized individuals.
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The primary complex of tuberculosis consists of a small TB lesion at the site of infection, TB lymphangitis, and TB lymphadenitis.
The primary complex of tuberculosis consists of a small TB lesion at the site of infection, TB lymphangitis, and TB lymphadenitis.
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Blood spread of TB occurs only through direct vessel erosion by a caseous focus in the lung.
Blood spread of TB occurs only through direct vessel erosion by a caseous focus in the lung.
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Bilharzial ulcers are responsible for 30% of common bladder lesions.
Bilharzial ulcers are responsible for 30% of common bladder lesions.
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Cystitis glandularis is characterized by cysts lined with transitional epithelium.
Cystitis glandularis is characterized by cysts lined with transitional epithelium.
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Brunn's nests are solid masses of transitional cells located in the mucosa due to cystitis.
Brunn's nests are solid masses of transitional cells located in the mucosa due to cystitis.
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Dysplasia in bilharzial cystitis may eventually progress to invasive carcinoma.
Dysplasia in bilharzial cystitis may eventually progress to invasive carcinoma.
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The presence of cystitis cystica can lead to visible pale mucosal vesicles that are several centimeters in diameter.
The presence of cystitis cystica can lead to visible pale mucosal vesicles that are several centimeters in diameter.
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Exogenous re-infection occurs when TB bacilli enter the body a second time after a patient has developed secondary tuberculosis.
Exogenous re-infection occurs when TB bacilli enter the body a second time after a patient has developed secondary tuberculosis.
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A type IV hypersensitivity reaction in secondary TB is characterized by increased phagocytic activity of phagocytes.
A type IV hypersensitivity reaction in secondary TB is characterized by increased phagocytic activity of phagocytes.
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Primary pulmonary tuberculosis typically develops in previously sensitized individuals, such as adults.
Primary pulmonary tuberculosis typically develops in previously sensitized individuals, such as adults.
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Secondary pulmonary TB is often localized to the apex of the left upper lobe due to increased local resistance.
Secondary pulmonary TB is often localized to the apex of the left upper lobe due to increased local resistance.
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Caseous necrosis and tissue damage in secondary TB are primarily due to the immune response triggered by hypersensitivity.
Caseous necrosis and tissue damage in secondary TB are primarily due to the immune response triggered by hypersensitivity.
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Blood spread of TB bacilli can lead to miliary tuberculosis when a large number of bacilli are present.
Blood spread of TB bacilli can lead to miliary tuberculosis when a large number of bacilli are present.
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Cavitation occurs slowly in secondary pulmonary TB, allowing for gradual dissemination along airways.
Cavitation occurs slowly in secondary pulmonary TB, allowing for gradual dissemination along airways.
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The right bronchus has more local resistance compared to the left bronchus, affecting TB localization.
The right bronchus has more local resistance compared to the left bronchus, affecting TB localization.
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Complications of tuberculosis include hemorrhage and amyloidosis.
Complications of tuberculosis include hemorrhage and amyloidosis.
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Complete fibrosis in small primary pulmonary lesions indicates healing of the infection.
Complete fibrosis in small primary pulmonary lesions indicates healing of the infection.
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Progression of tuberculosis only occurs with a large number of bacilli and low immunity.
Progression of tuberculosis only occurs with a large number of bacilli and low immunity.
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Schistosoma mansoni primarily affects the genitourinary system.
Schistosoma mansoni primarily affects the genitourinary system.
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The incidence of bilharziasis is highest in the United States.
The incidence of bilharziasis is highest in the United States.
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Fibrotic tuberculosis occurs as a result of high immunity and a small number of bacilli.
Fibrotic tuberculosis occurs as a result of high immunity and a small number of bacilli.
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Swallowing infected sputum can lead to intestinal tuberculosis.
Swallowing infected sputum can lead to intestinal tuberculosis.
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Bilharzial polyps can only be single and are always sessile.
Bilharzial polyps can only be single and are always sessile.
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The common lesions of bilharziasis include sandy patches and bilharzial ulcers.
The common lesions of bilharziasis include sandy patches and bilharzial ulcers.
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Complications of secondary pulmonary tuberculosis do not include hemoptysis.
Complications of secondary pulmonary tuberculosis do not include hemoptysis.
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Infected sputum may only affect the lungs and not other body parts.
Infected sputum may only affect the lungs and not other body parts.
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Schistosoma hematobium produces lesions primarily in the intestines.
Schistosoma hematobium produces lesions primarily in the intestines.
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Study Notes
Infectious Diseases - Tuberculosis
- Tuberculosis (TB) is a chronic granulomatous inflammation caused by Mycobacterium tuberculosis.
- TB is a common, communicable, chronic infectious disease.
- Risk factors include poverty, crowding, malnutrition, chronic illnesses like diabetes and lung disease, alcoholism, and AIDS.
Causative Bacteria
- The causative bacteria are human tubercle bacilli (acquired by inhalation) and bovine tubercle bacilli (acquired by consuming infected milk).
- Mycobacteria are slender, aerobic, non-motile, gram-positive rods, stained with Ziehl-Neelsen stain.
Methods of Infection
- Inhalation of infected droplets coughed or sneezed from individuals with open pulmonary TB or dust contaminated with infected sputum.
- Ingestion of contaminated milk or self-swallowing of infected sputum from an open case of pulmonary TB.
- Skin inoculation with infected materials (very rare).
- Transplacental route (congenital TB, rare).
Host Response to TB Bacilli
- Proliferative reaction
- Exudative reaction
Proliferative Tissue Reaction (Tubercle Formation)
- Initial response involves neutrophil attraction, quickly destroyed by the organisms.
- Macrophages are attracted after the first day.
- Bacteria multiply inside macrophages, leading to rupture and release of more organisms.
- Macrophages modify to resemble epithelioid cells.
- Epithelioid cells aggregate to form granulomas.
- Some epithelioid cells fuse to form Langhan's giant cells.
- Lymphocutes and fibroblasts are found at the periphery of the granuloma.
- Caseation necrosis occurs at the centre of the granuloma.
- Tubercles fuse, forming small, rounded, visible grey follicles (1-2 mm), becoming grayish yellow and cheesy with caseation.
Exudative Reaction
- In serous membranes (lung and meninges), protein-rich, yellowish serous exudate is formed.
- Infiltration of large numbers of lymphocytes, a small number of epithelioid cells, and Langhans' giant cells with rapid caseation.
Fate of Tuberculosis Granuloma
- Dystrophic calcification in caseous material or hyalinized lesions.
- Enlargement of the lesion and fibrosis.
- Cold abscesses form if caseation increases, liquefying material accumulating in bones, joints, lymph nodes and epididymis.
- Sinus formation occurs when cold abscesses extend into surrounding tissue (e.g., discharging caseous material on the skin).
Immunization Against TB
- BCG vaccine (attenuated bovine TB bacilli) induces cell-mediated immunity and delayed hypersensitivity.
- Tuberculin (Mantoux) skin test: intradermal injection of PPD (purified protein derivative), inducing delayed hypersensitivity in infected or previously infected individuals. A positive test shows indurated area (≥5 mm) peaking in 48-72 hours.
Spread of TB Infection
- Local spread by macrophages carrying bacilli.
- Spread through natural passages:
- Lung to pleura
- Transbronchial spread to adjacent lung segments
- Tuberculous salpingitis to peritoneal cavity
- Infected sputum to larynx
- Renal lesions to ureter and urinary bladder
- Lymphatic spread via lymphatic vessels to regional lymph nodes.
- Blood spread via lymphatic connections (thoracic duct) causing isolated organ TB or miliary TB (many organs affected).
Types of TB
- Primary TB
- Secondary TB (Reactivation)
Primary TB
- Initial infection by TB bacilli.
- Primarily affects non-immunized children.
- Most patients are asymptomatic or have a mild flu-like illness.
- Sites include lung, tonsils, intestines, and skin.
- Characteristic of a primary complex (small TB lesion at infection site, TB lymphangitis, TB lymphadenitis).
Secondary (Reactivation) TB
- Reactivation of a dormant primary lesion.
- Affects previously sensitized hosts, mostly adults.
- Often occurs decades after initial illness, especially with weakened host defenses.
- Can also be due to exogenous reinfection.
- Immunity due to increasing activity of macrophages, and a decrease in TB bacilli reaching lymph nodes.
- Hypersensitivity is increased, causing tissue damage with caseous necrosis.
Pulmonary Tuberculosis
- Type of TB developing in a previously unsensitized patient (first infection with TB bacilli), which occurs more commonly in children.
- Infection happens by inhalation of human TB bacilli.
- Bacilli commonly implant in distal air spaces of the lower part of upper lobe or upper part of lower lobe, often near the pleura ("subpleural").
Fate of Primary Pulmonary Complex
- Healing: Complete fibrosis in small lesions
- Fibrous capsulation and central calcification in larger lesions.
- Spread: Direct spread causing TB pneumonia and pleurisy/pericarditis.
- Blood spread: Small no. of bacilli destroyed by RES; Moderate no. of bacilli isolate organ TB, Large no. of bacilli causes miliary TB.
- Bronchial spread causes TB bronchopneumonia.
Secondary Pulmonary TB (Reactivation)
- Arises in a previously sensitized host.
- Common in adults.
- Primarily from reactivation of dormant primary lesions decades after initial infection; particularly when host resistance is less.
- Also possible from exogenous reinfection.
Secondary Pulmonary TB (Localization)
- Classically localized to the apex of one or both upper lobes, due to less resistance in these areas, including less blood supply and greater aeration compared to other lung regions.
- Right lung bronchus in alignment with trachea more so than left lung.
- Cavities occur rapidly in secondary TB, causing erosion into airways and dissemination.
- This leads to the patient producing sputum containing bacilli—an important source of infectivity.
Course of TB Disease
- Depends on the infecting bacilli dose and host immunity/hypersensitivity state.
- Regression: Low bacilli count and strong immunity; lesion heals through fibrosis (fibrotic TB).
- Progression: Moderate bacilli count and moderate immunity: chronic, fibrocaseous pulmonary TB. Large bacilli count and low immunity: acute tuberculous bronchopneumonia.
Complications of Secondary Pulmonary Tuberculosis
- Hemoptysis
- Rupture of cavity into pleural sac → pneumothorax or pyopneumothorax.
- Right-sided heart failure due to extensive lung fibrosis
- Secondary amyloidosis
- Other lung, larynx, tonsils or tongue infections from infected sputum
- Intestinal TB from swallowing infected sputum.
Clinical Picture of TB
- Weight loss, sweating, night fever
- Chest pain (pleurisy), dyspnea (due to pleural effusion)
- Hemoptysis
Parasitic Infections - Schistosomiasis (Bilharziasis)
- Chronic granulomatous disease caused by schistosoma infection.
- Endemic in Egypt.
- Caused by two species:
- Schistosoma hematobium: affects the genitourinary system.
- Schistosoma mansoni: affects the digestive system..
Sites of Bilharzial Lesions
- Schistosoma hematobium ova produce lesions in the urinary bladder, ureters, urethra, seminal vesicles, prostate, spermatic cord, epididymis, vulva, vagina, and fallopian tubes; ova can spread to other tissues, including the lungs.
- Schistosoma mansoni ova produce lesions mainly in the intestine; ova fail to engage in vascular wall and are carried by blood to the liver as emboli.
Bilharziasis of the Urinary Bladder (Bilharzial Cystitis)
- Pathological lesions are most marked in the trigone, around ureteric orifices, and in the posterior wall of the urinary bladder.
- Lesions frequently include sandy patches (calcified ova deposits), billharzial polyps (sessile, pedunculated, or branched), and bilharzial ulcers (single or multiple, small or large).
Epithelial Changes in Urinary Bladder Bilharziasis
- Hyperplasia: Thickening of transitional epithelium due to inflammation.
- Brunn's nests: Masses of transitional cells in the submucosa due to transitional epithelium dipping into lamina propria.
- Cystitis cystica: Cysts lined by transitional epithelium due to Brunn's nests.
- Cystitis glandularis: Cysts lined with mucin-secreting columnar cells (metaplasia of transitional epithelium)
- Squamous metaplasia and leukoplakia: Thick white patches (leukoplakia) due to keratinization, premalignant.
- Dysplasia and carcinoma in situ: Transitional or metaplastic squamous epithelium affected. Premalignant lesions that can progress to invasive cancer.
Complications of Bilharzial Cystitis
- Hematuria
- Secondary bacterial infections (e.g., calcium phosphate stones, fistulae).
- Bladder neck obstruction due to fibrosis.
- Bilateral hydroureter and hydronephrosis may occur.
- Chronic renal failure due to bilateral hydronephrosis.
- Carcinoma of the urinary bladder
- Pulmonary bilharziasis
- Contracted urinary bladder
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Description
Test your knowledge on tuberculosis, its causes, transmission, and diagnostic methods. This quiz covers aspects such as bacteria involved, immunization, and the body's immune response to infection. Understand key concepts and terminology related to TB.
