Tuberculosis and Leprosy: Clinical Detection, Treatment, and Pathophysiology

Tuberculosis (TB)

Clinical Methods of Detecting TB

Tuberculosis is a major infectious disease caused by Mycobacterium tuberculosis. Accurate diagnosis is essential for effective treatment and control. Several clinical methods are used to detect TB:

• Tuberculin Skin Test (Mantoux Test): Involves intradermal injection of purified protein derivative (PPD) into the skin. A small bleb develops, and the size of induration is measured after 48-72 hours. Interpretation:

  • 5-9 mm: Positive if person is in category 1 (high risk)

  • 10-14 mm: Positive if person is in category 2 (moderate risk)

  • 15 mm: Positive if person is in category 3 (low risk)

• Chest X-rays: Used to detect lung abnormalities associated with TB infection, such as infiltrates or cavities.

• Acid-fast staining in sputum: Sputum samples are stained to identify acid-fast bacilli, characteristic of M. tuberculosis.

• Cultural isolation: Growth of M. tuberculosis from clinical specimens confirms diagnosis.

Treatment and Prevention of TB

Treatment of TB requires prolonged use of multiple antibiotics to prevent resistance and ensure eradication of the bacteria.

• Standard Treatment: 6-24 months of at least 2 drugs.

• Initial Phase: Four drugs—isoniazid (INH, inhibits mycolic acid synthesis), rifampin (RIF), ethambutol (EMB), and pyrazinamide (PZA)—taken daily for 8 weeks.

• Continuation Phase: INH and RIF for 18 weeks.

• Combination Therapy: Rifater (isoniazid, rifampin, pyrazinamide) may be supplemented with ethambutol.

• Drug Resistance: Many strains of M. tuberculosis are resistant to at least one commonly used drug.

• Vaccine: Bacille Calmette-Guerin (BCG) vaccine is used in other countries for prevention.

Key Terms

• Acid-fast bacilli: Bacteria that retain certain stains even after being washed with acid alcohol, characteristic of Mycobacterium species.

• Induration: Hardening of the skin at the site of tuberculin injection, measured to assess immune response.

Leprosy (Hansen's Disease)

Etiology and Pathogenesis

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (Hansen's bacillus). It primarily affects the skin, mucous membranes, and peripheral nerves.

• Strict Parasite: Cannot be grown on artificial media or tissue culture; can grow in armadillos.

• Slow Growth: Slowest growing of all mycobacteria; multiplies within host cells in large packets called globi.

• Transmission: Direct contact and respiratory routes; not highly virulent. Health and living conditions influence susceptibility.

• Genetic Susceptibility: May be associated with specific genetic markers.

Course of Infection and Disease

• Phagocytosis: Macrophages ingest bacilli, but weakened immune response may allow survival and multiplication.

• Incubation: 2-5 years; bacilli grow slowly in skin macrophages and peripheral nerve cells if untreated.

• Symptoms: Numbness in hands and feet, loss of heat and cold sensitivity, muscle weakness, thickened earlobes, chronic stuffy nose.

Clinical Forms of Leprosy

Leprosy presents in two major clinical forms, distinguished by immune response and bacterial load.

Tuberculoid (Paucibacillary) Leprosy	Lepromatous (Multibacillary) Leprosy
Few bacilli in lesions	Many bacilli in lesions
Shallow skin lesions in many areas	Numerous deeper lesions concentrated in cooler areas of body
Loss of pain sensation in lesions	Sensory loss more generalized; occurs late in disease
No skin nodules	Gross skin nodules
Occasional mutilation of extremities	Mutilation of extremities common
Reactive to lepromin*	Not reactive to lepromin
Lymph nodes not infiltrated by bacilli	Lymph nodes massively infiltrated by bacilli
Well-developed cell-mediated (T-cell) response	Poorly developed T-cell response

*Lepromin is an extract of the leprosy bacillus injected intradermally, like tuberculin, to detect delayed allergy to leprosy.

Lepromatous (Multibacillary) Leprosy

• Deeply nodular infection causes severe disfigurement of the face and extremities.

• Many bacteria found in skin scrapings.

Diagnosis of Leprosy

• Combination of symptoms, microscopic examination of lesions, and patient history.

• Detection of acid-fast bacilli in clinical samples.

Treatment and Prevention of Leprosy

• Multidrug therapy: Essential to prevent resistance and ensure cure.

• Prevention: Requires constant surveillance of high-risk populations.

• Vaccine: No definitive vaccine; BCG vaccine may provide some protection.

Key Terms

• Globi: Large packets of multiplying M. leprae within host cells.

• Lepromin Test: Used to assess immune response to leprosy bacillus.

Additional info:

• Both TB and leprosy are caused by mycobacteria, which are acid-fast due to their mycolic acid-rich cell walls.

• Cell-mediated immunity is crucial for controlling both diseases; poor T-cell response leads to more severe forms.