Infectious Disease: TB

Question 1

Defintion

Answer 1

Infectious disease caused by the bacterium Mycobacterium tuberculosis

Question 2

Aetiology

Answer 2

Mycobacterium Tuberculosis

Question 3

Risk factors

Answer 3

Malnutrition
Immunodeficiency
History of TB
Travel of migration
Crowded living area

Question 4

Mycobacterium tuberculosis

Answer 4

• small rod shaped bacterium
• waxy coating (MYCOLIC ACID) that makes gram staining ineffective = acid fastness
• only can be stained by Zeihl-Nielsen stain
• turns TB bright red against blue background

Question 5

Pathophysiology

Answer 5

Transmitted via inhalation of respiratory droplets
Bacteria reach pulmonary alveoli and engulfed by alveoli macrophages and replicate within them.
Lymphocytes surround the infected macrophages along the fibroblast and this cases a granuloma formation.
The Ghon focus is composed of tubercle-laden macrophages. The combination of a Ghon focus and hilar lymph nodes is known as a Ghon complex
This prevents dissemination of the bacteria (prevents extra pulmonary TB).
Inside these lesions, the bacteria develop abnormal cell death in the centre (caseous necrosis) and can eliminate the bacteria.
This is sometimes referred to as LTBI - latent tuberculosis infection

10% chance = LTBI develop into active TB during Px lifetime. - The risk is greatest during the first two years of infection.
- Active TB typically presents with fever, night sweats, weight loss and cough, lasting usually more than 2-3 weeks
- Alternatively, if there is a failure of the above mechanism…The bacteria may gain entry to the bloodstream can spread throughout the body and set up many foci of infection (tubercles) (e.g. miliary TB). This is extra-pulmonary TB

Question 6

Symptoms

Answer 6

Children often not infectious (older children may be)
● Cough
● Fever
● Weight loss
● Malaise
● Night sweats
● Pleuritic chest pain
● Haemoptysis
● Lymphadenopathy
● Erythema nodosum- tender red bumps on skin of shin

Question 7

Diagnosis

Answer 7

Latent TB
FIRST LINE = Mantoux, IFN gamma, FBC
< 6mm: Negative - no significant hypersensitivity to tuberculin protein
= Previously unvaccinated individuals may be given the BCG
6 - 15mm: Positive - hypersensitive to tuberculin protein
= Should not be given BCG. May be due to previous TB infection or BCG
> 15mm: Strongly positive - strongly hypersensitive to tuberculin protein
= Suggests tuberculosis infection.

Active TB
CXR - fibronodular opacities in upper lobes with or without cavitation
GOLD STANDARD = Sputum Culture - most sensitive and specific test

Question 8

Active Treatment

Answer 8

Medication:
- Isoniazid (6 months) = inhabits mycolic acid synthesis (+ Pyridoxine to prevent peripheral neuropathy)
- Rifampicin (6 months) = inhibits bacterial DNA dependent RNA polymerase preventing transcription of DNA into mRNA
- Pyrazinamide (First 2 months) = converted by pyrazinamidase into pyrazinoic acid which in tuns inhibits fatty acid synthase (FAS)
- Ethambutol (First 2 months) = inhibits the enzyme arabinosyl transferase which polymerises arabinose into abarabinan

Question 9

Medication Side Effects

Answer 9

Isoniazid
- Peripheral neuropathy: Vit B6
- Hepatitis
- Agranulocytosis
Rifampicin
- Hepatits
- Orange/red urine
- Flu like symptoms
Pyrazinamide
- Hyperuricemia (gout)
- Arthralgia
- Myalgia
- Hepatitis
Ethambutol
- Optic neuritis - check visual acuity before Tx

Question 10

BCG Vaccine

Answer 10

Intradermal infection of live attenuated (weakened) TB. It offers protection against severe and complicated TB but is less effective at protecting against pulmonary TB.
- Only given if Mantoux test comes back negative
They are also assessed for the possibility of immunosuppression and HIV due to the risks related to a live vaccine BCG vaccine is offered to patients that are at higher risk of contact with TB:
● Neonates born in areas of the UK with high rates of TB
● Neonates with relatives from countries with a high rate of TB
● Neonates with a family history of TB
● Unvaccinated older children and young adults (< 35) who have close contact with TB
● Unvaccinated children or young adults that recently arrived from a country with a high rate of TB
● Healthcare workers

Question 11

Complications

Answer 11

ARDS,
Pneumothorax,
Empyema

Question 12

Latent TB treatment

Answer 12

3 months of isoniazid (with pyridoxine) and rifampicin OR 6 months of isoniazid (with pyridoxine)