M8: TB and Respiratory pathogens

Question 1

What is TB

Answer 1

Granulomatous infection (chronic inflammatory reaction) caused by M. tuberculosis

Question 2

Clinical features of TB

Answer 2

Persistent cough (blood in sputum)
Fatigue 
Chest pain 
Loss of apetite
Weight loss
Fevers, night sweats and chills

Question 3

Oral manifestations of TB

Answer 3

Ulcer on tongue

Nodules, peripheral granulomas and indurated patches

Question 4

General features of mycobacteria

Answer 4

Aerobic
Curved/ straight rods
Acid-fast (mycelia acids in waxy cell wall)

Question 5

Features of M. tuberculosis

Answer 5

Slow growing
Colonies = “rough buff and tough”
Detected through ZN stain of sputum smear

Question 6

How can rapid detection of M. tuberculosis be done

Answer 6

1. Direct staining
2. Nucleic acid amplification techniques
3. Culture based methods
4. Biomarkers

Question 7

Outline pathogenesis of TB (short answer)

Answer 7

M. tuberculosis survives in alveolar macrophages

Cell mediated response causes clinical features of TB, tissue destruction and pathological cx

Question 8

Outline pathogenesis of TB (long answer)

Answer 8

1. Infection in lung with M. tuberculosis and replication within macrophages
2. Initial lesion = Ghon focus and causes a primary complex
3. Macrophage carried to hilar lymph nodes causing additional foci
4. Seeding by dissemination to organs and tissues = Miliary TB where the focus ruptures into blood vessels causing numerous granulomas

Question 9

What happens to the primary Gohn complex

Answer 9

• T-cells/lumphokines/macrophages cause granuloma formation with caseation and necrotic tissue
• Limits primary infection but the mycobacteria persists within
• This can be reactivated to give post primary disease TB

Question 10

What are the less common initial focus of infection for primary TB

Answer 10

Meningitis
Pleurisy
Kidney, spine, bones, joints
Skin

Question 11

What happens in post primary TB

Answer 11

1. Primary complex resolves and there is reactivation of dormant foci in lobes of lung - likely in immunocompromised
2. Form large granulomas with caseation and the infection becomes more serious and damaging (wasting and fever symptoms)
3. Tuberculoma expands into airways leading to bacilli in sputum = open infectious patient
4. Further spread and lesions develop in bronchial tree, larynx, trachea, intestine and bladder

Question 12

What is the result of TB reactivation

Answer 12

Numerous minute lesions with high number of bacilli, rapidly fatal because it leads to CRYPTIC DISSEMINATED TB

Question 13

How is TB transmitted

Answer 13

Inhalation in cough droplets from open individuals (only sputum positive are infections) - occurs within households and areas of overcrowding

Question 14

How is TB controlled/ prevented

Answer 14

1. early detection - rapid diagnosis
2. effective therapy of open individuals
3. reduction in over vrowding
4. vaccination

Question 15

What vaccine is given for TB

Answer 15

BCG containing live attenuated strain of M. bovis via intracutaneous injection

• variable efficacy = better in children
• long term use of BCG controls spread of virus

Question 16

How is vaccination for TB tested

Answer 16

Skin test = Mantoux test

When there is lack of inflammatory response, the BCG is needed

Question 17

Why is the Mantoux test limited

Answer 17

Cannot differentiate

• active disease
• quiescent infections
• previous BCG vaccination
• other mycobacterial infections

Question 18

Outline TB treatment

Answer 18

Intensive phase (2 months)
Rifampicin 
Isoniazid 
Pyrazinamide 
Ethambutol 

Continuation phase (6-9 months)
Rifampicin
Isoniazid

Question 19

What do upper respiratory tract infections include

Answer 19

Acute inflammatory processes mainly involving: nose, paranasal sinuses, middle ear, laryngeal, post. pharynx, tonsils

Most frequently = common colds, sore throats

Question 20

What do lower respiratory tract infections include

Answer 20

Below larynx

Productive cough, chest pain, pneumonia, bronchitis, bronchiectasis, whooping cough

Question 21

Features of haemophilia species

Answer 21

Gram -ve, Faculative anaerobes, CO2 enhances growth

Requires X factor (haemin) or V factor NAPD for growth

Question 22

Pathogenesis of H. influenzae

Answer 22

Important in young children as there is possible penetration of submucosa of nasopharynx

1. H. influenza causes pharyngitis (preceding viral infection)
2. Can cause sinusitis (epiglottiitis can be severe - asphyxia danger)
3. Invasive disease
4. Common bloodstream invasion
5. Pneumonia, meningitis type b

Can cause pulmonary disease in adults with preceding viral infection/ chronic bronchitis

Question 23

Features of C. diptheriae

Answer 23

Aerobic/ facultative anaerobic
Gram +ve diptheriods or coryneforms
Causes diphtheria
Spread by person-person contact in nasopharyngeal secretions (children susceptible)

Question 24

What are the 3 types of C. diptheriae

Answer 24

Gravis
Intermedius
Mitis

Question 25

Pathogenesis C. diptheriae

Answer 25

1. Inflammatory response causes necrotic tissue and pus production
2. Odema and swelling causes respiratory obstruction
3. Clotting of exudate causes pseudomembrane which suffocates that patient
4. Bacteria produces powerful toxins into bloodstream which have affinity for heart, nerve endings and adrenal gland - leads to heart failure

Question 26

Outline treatment for diphtheria

Answer 26

Patient isolation
Antibiotics = Penicillin, Tetracycline, Clindamycin
Early antitoxin therapy