Tuberculosis (TB) is a chronic infection primarily affecting the lungs and is a leading cause of morbidity and mortality globally, especially in low-income regions. It can be classified as open or closed, pulmonary or extrapulmonary, and transmission occurs mainly through airborne droplets from infected individuals. Treatment typically involves a combination of first-line drugs and, if necessary, second-line medications, with appropriate therapy usually curative for drug-susceptible cases.

1. Covered by: Arwa H. Al-Onayzan.

2. Tuberculosis

3. • Tuberculosis (TB):
• Is a chronic, progressive infection, often with a period of latency
following initial infection.
• TB most commonly affects the lungs.
• TB is a leading infectious cause of morbidity and mortality in adults
worldwide, killing about 1.3 million people in 2012.
• Most of them in low- and middle-income countries.
• HIV/AIDS is the most important factor predisposing to TB infection and
mortality in parts of the world where both infections are prevalent.

4. • It can be classified as:
I. Open tuberculosis (Is consider infectious and occur when the TB
bacteria in the lung spread into the air and infect others).
II. Closed tuberculosis (Is not consider infectious because it cannot
spread into the air, such as, lymph node TB).
• It can be classified as:
I. Pulmonary tuberculosis (Affect only the lung).
II. Extrapulmonary tuberculosis (Affect lymph node, bone, ect).
• It can be classified according to pathogesis  see next slide (table)

5. • TB properly refers only to disease caused by Mycobacterium tuberculosis (for
which humans are the main reservoir).
• It can also results from other mycobacteria, M. bovis, M. africanum, and M.
microti—together known as the M. tuberculosis complex.
• TB results almost from inhalation of airborne particles (droplet nuclei)
containing M. tuberculosis.
• They disperse primarily through coughing, singing, and other forced respiratory
maneuvers by people who have active pulmonary TB and whose sputum
contains a significant number of organisms.
• TB of the tonsils, lymph nodes, abdominal organs, bones, and joints was once
commonly caused by ingestion of milk or milk products (eg, cheese)
contaminated with M. bovis.

6. I. M. tuberculosis bacilli initially cause a primary infection. it asymptomatic
and followed by a latent (dormant) phase.
II. Infection requires inhalation of particles small enough to traverse in the
lung, usually in the subpleural airspaces of the middle or lower lobes.
III. To initiate infection, M. tuberculosis bacilli must be ingested by alveolar
macrophages.
IV. Bacilli that are not killed by the macrophages, replicate inside them,
ultimately killing the host macrophage (with the help of CD8 lymphocyte);
inflammatory cells are attracted to the area, causing a focal pneumonitis.
V. Some infected macrophages migrate to regional lymph nodes (eg, hilar,
mediastinal), where they access the bloodstream and spread over body.
VI. The balance between the host’s resistance and microbial virulence
determines whether the infection ultimately resolves without treatment,
remains dormant, or becomes active.
VII. Infectious foci may leave fibronodular scars in the apices of one or both
lungs (Simon foci, which usually result from hematogenous seeding from
another site of infection) or small areas of consolidation (Ghon foci). A
Ghon focus with lymph node involvement is a Ghon complex, which, if
calcified, is called a Ranke complex.
VIII.Tuberculin skin test and interferon-gamma release blood assays (IGRA)
become positive during the latent stage of infection.

7. • In active pulmonary TB, patients may have no symptoms, except “not feeling
well,” anorexia, fatigue, and weight loss, which develop gradually over several
weeks, or they may have more specific symptoms:
I. Cough is most common. At first, it may be minimally productive of yellow or green
sputum, usually when awakening in the morning, but cough may become more
productive as the disease progresses.
II. Hemoptysis occurs only with cavitary TB (due to granulomatous damage to vessels).
III. Low-grade fever is common but not invariable.
IV. Night sweats are a classic symptom but are neither common in nor specific for TB.
V. Dyspnea may result from lung parenchymal damage.
• Extrapulmonary TB causes various systemic and localized manifestations
depending on the affected organs.

8. I. Chest x-ray (a multinodular infiltrate above or behind
the clavicle is most characteristic of active TB)  see pic.
II. Acid-fast stain and culture (Gold standard, samples are
best prepared with Ziehl-Neelsen or Kinyoun stains for
conventional light microscopy).
III. Tuberculin skin test (TST)  see pic
IV. or interferon-gamma release assay (IGRA) (is a blood
test based on the release of interferon-γ by lymphocytes
exposed in vitro to TB-specific antigens).
V. When available, nucleic acid–based testing (has not
been approved but can be extremely useful, used for
fixed tissues eg, for biopsied lymph node).

9. • Most patients with TB can be treated as outpatients, with instructions including:
• Staying at home.
• Avoiding visitors (except for previously exposed family members).
• Covering coughs with a tissue or elbow.
• The main indications for hospitalization are:
• Serious concomitant illness
• Need for diagnostic procedures
• Social issues (eg, homelessness)
• Need for respiratory isolation, as for people living in congregate settings
• Treatment regimen: 2-mo initial intensive phase and 4- to 7-mo continuation phase.
• The first-line drugs isoniazid (INH), rifampin (RIF), pyrazinamide (PZA), and ethambutol (EMB)
are used together in initial treatment.
• The second-line drugs used if there is resistance such as, aminoglycosides (streptomysin) and
fluoroquinolones (levofloxacin, moxifloxacin).

10. • In immunocompetent patients with drug-susceptible pulmonary TB, even
severe disease with large cavities, appropriate therapy is usually curative if it
is instituted and completed.
• TB causes or contributes to death in about 10% of cases, often in patients
who are debilitated for other reasons.
• Disseminated TB and TB meningitis may be fatal in up to 25% of cases
despite optimal treatment.
• TB is much more aggressive in immunocompromised patients and, if not
appropriately and aggressively treated, may be fatal.

11. I. General preventive measures (eg, staying at home, avoiding
visitors, covering coughs with a tissue or hand).
II. Vaccination:
The BCG vaccine, made from an attenuated strain of M. bovis is given
to > 80% of the world’s children.
Average efficacy is probably only 50%.
BCG clearly reduces the rate of extrathoracic TB in children, especially TB
meningitis, and may prevent TB infection.
IGRAs are not influenced by BCG vaccination.
TST is influenced by BCG vaccination.

12. • Merk manual website:
• http://www.msdmanuals.com/professional/infectious-
diseases/mycobacteria/tuberculosis-tb
• Medscape website:
• http://emedicine.medscape.com/article/230802-overview#a5