What is primary tuberculosis?

Primary Tuberculosis (Primary TB)

Primary tuberculosis is the initial infection caused by Mycobacterium tuberculosis in a person who has never been previously exposed to the bacterium. It typically occurs in children or young adults but can also affect people of any age.

Key Features of Primary TB

Aspect	Details
Cause	First exposure to M. tuberculosis
Immunity	Host has no pre-existing immunity
Common Site	Mid/lower zones of the lungs (usually subpleural)
Characteristic Lesion	Ghon focus (initial lesion in lung parenchyma)
Lymph Node Involvement	Ghon complex = Ghon focus + involved hilar lymph nodes
Immune Response	Cell-mediated immunity develops over 2–3 weeks
Outcome	Usually heals with fibrosis and calcification; may become latent

Pathogenesis of Primary TB

1. Inhalation of bacilli → reaches alveoli

2. Bacilli are engulfed by alveolar macrophages

3. Initiates granulomatous inflammation

4. Formation of Ghon focus (small area of caseation necrosis)

5. Spread to regional lymph nodes → forms Ghon complex

6. In most healthy individuals:

   • The infection is contained

   • Becomes latent TB

7. In immunocompromised individuals:

   • Progresses to progressive primary TB or disseminated TB

Ghon Focus vs Ghon Complex

Term	Description
Go on, focus	Caseating granuloma in the lung parenchyma (usually subpleural)
Ghon complex	Ghon focus + involved hilar or paratracheal lymph nodes

With healing, this complex may calcify, forming a Ranke complex (healed primary TB).

Clinical Features (Often Asymptomatic)

• Low-grade fever

• Fatigue

• Mild cough

• Rarely, mild chest pain

• Often discovered incidentally on chest X-ray

Complications (in a few cases)

• Progressive primary TB (especially in immunocompromised)

• Miliary TB (disseminated)

• TB meningitis or bone TB (in children)

Summary

Primary TB
First exposure to TB bacillus
Common in children
Ghon focus and Ghon complex formation
Usually asymptomatic or mild
May progress, heal, or become latent