Tuberculosis

Question 1

Characteristics of Mycobacterium Tuberculosis

Answer 1

Aerobic, rod shaped bacterium. Acid fast due to mycolic acids in wall. Primarily intracellular. Induces a granulomatous response

Question 2

Transmission of TB

Answer 2

Aerosol droplets – most commonly occurs with close contact. Not transmitted by fomites

Question 3

Primary infection

Answer 3

Creates a granuloma (ghon lesion) at the alveoli. Alveolar macrophages are initial defense against organisms reaching the parenchyma. Spread quickly via lymphatics to hilar lymph nodes and to the apices of the lung via blood. In majority of cases, infection is limited by host immune system. Local tissue response (granuloma).

Question 4

How does clinically apparent primary tb occur

Answer 4

When host cell defenses are inadequate to control the infection. This occurs in alcoholism, with certain medications, and HIV. Happens 5% of the time

Question 5

Delayed hypersensitivity

Answer 5

Happens a few weeks after primary infection. Cell mediated immunity develops and causes caseating granulomas. Then fibrosis /scarring occurs with deposition of calcium.

Question 6

Latent TB

Answer 6

The bacterium may not be completely eliminated from host, so some organisms remain latent. Majority of patients will never have further difficulty, but sometimes can reactivate if immune system is weak. This happens in 10% of normals.

Question 7

Tuberculin skin test

Answer 7

Purified protein derived from tubercle bacillus injected intradermally. Individuals exposed to Tb will develop a cellular immunity response. This doesn’t distinguish from active infection though. False negative if underlying disease with depressed immune system. False positive if had other mycobacterial infections

Question 8

IGRA

Answer 8

Cells are exposed to antigen. If IFN gamma isreleased then it is clear the patient has been exposed to TB

Question 9

Latent Tb in terms of PPD/IGRA

Answer 9

+PPD or +IGRA but no evidence of active disease

Question 10

Where are cavitary lesions from reactivation TB most common? Why?

Answer 10

In the upper lobes, due to hematogenous spread. High pO2 and relatively less perfusion, so great for survival.

Question 11

Clinical features of TB

Answer 11

Wasting, scarring and loss of lung tissue. Respiratory function is generally preserved though. Also oxygenation tends to be surprisingly preserved. Cough, sputum production, hemoptysis. Insidious onset.

Question 12

Miliary TB

Answer 12

Progressive widely disseminated hematogenous spread of TB. Can arise as a result of progressive primary infection or via reactivation.

Question 13

Treatment of TB?

Answer 13

Rifampin, Isoniazid, Pyrazinamide, Ethambutol

Treat latent TB

Question 14

Where are nontuberculous mycobacteria found?

Answer 14

In soil and water

Question 15

Most common non-tuberculous mycobacteria?

Answer 15

Microbacterium avium complex. MAC

Question 16

What type of disease does MAC cause?

Answer 16

Patients with underlying lung disease and AIDS patients will get sick.