M8: TB and Respiratory pathogens Flashcards
1. List morphological and cultural properties of mycobacteria and the distinguishing features of M. tuberculosis 2. Describe aetiology and pathogenesis of TB 3. Summarise methods for TB diagnosis 4. Outline principles of TB treatment 5. Outline modes of spread and control of TB 6. Describe the main types of URT and LRT infections 7. Outline features and pathogenic potential of common respiratory pathogens: H. influenzae, C. diptheriae (26 cards)
What is TB
Granulomatous infection (chronic inflammatory reaction) caused by M. tuberculosis
Clinical features of TB
Persistent cough (blood in sputum) Fatigue Chest pain Loss of apetite Weight loss Fevers, night sweats and chills
Oral manifestations of TB
Ulcer on tongue
Nodules, peripheral granulomas and indurated patches
General features of mycobacteria
Aerobic
Curved/ straight rods
Acid-fast (mycelia acids in waxy cell wall)
Features of M. tuberculosis
Slow growing
Colonies = “rough buff and tough”
Detected through ZN stain of sputum smear
How can rapid detection of M. tuberculosis be done
- Direct staining
- Nucleic acid amplification techniques
- Culture based methods
- Biomarkers
Outline pathogenesis of TB (short answer)
M. tuberculosis survives in alveolar macrophages
Cell mediated response causes clinical features of TB, tissue destruction and pathological cx
Outline pathogenesis of TB (long answer)
- Infection in lung with M. tuberculosis and replication within macrophages
- Initial lesion = Ghon focus and causes a primary complex
- Macrophage carried to hilar lymph nodes causing additional foci
- Seeding by dissemination to organs and tissues = Miliary TB where the focus ruptures into blood vessels causing numerous granulomas
What happens to the primary Gohn complex
- 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
What are the less common initial focus of infection for primary TB
Meningitis
Pleurisy
Kidney, spine, bones, joints
Skin
What happens in post primary TB
- Primary complex resolves and there is reactivation of dormant foci in lobes of lung - likely in immunocompromised
- Form large granulomas with caseation and the infection becomes more serious and damaging (wasting and fever symptoms)
- Tuberculoma expands into airways leading to bacilli in sputum = open infectious patient
- Further spread and lesions develop in bronchial tree, larynx, trachea, intestine and bladder
What is the result of TB reactivation
Numerous minute lesions with high number of bacilli, rapidly fatal because it leads to CRYPTIC DISSEMINATED TB
How is TB transmitted
Inhalation in cough droplets from open individuals (only sputum positive are infections) - occurs within households and areas of overcrowding
How is TB controlled/ prevented
- early detection - rapid diagnosis
- effective therapy of open individuals
- reduction in over vrowding
- vaccination
What vaccine is given for TB
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
How is vaccination for TB tested
Skin test = Mantoux test
When there is lack of inflammatory response, the BCG is needed
Why is the Mantoux test limited
Cannot differentiate
- active disease
- quiescent infections
- previous BCG vaccination
- other mycobacterial infections
Outline TB treatment
Intensive phase (2 months) Rifampicin Isoniazid Pyrazinamide Ethambutol
Continuation phase (6-9 months)
Rifampicin
Isoniazid
What do upper respiratory tract infections include
Acute inflammatory processes mainly involving: nose, paranasal sinuses, middle ear, laryngeal, post. pharynx, tonsils
Most frequently = common colds, sore throats
What do lower respiratory tract infections include
Below larynx
Productive cough, chest pain, pneumonia, bronchitis, bronchiectasis, whooping cough
Features of haemophilia species
Gram -ve, Faculative anaerobes, CO2 enhances growth
Requires X factor (haemin) or V factor NAPD for growth
Pathogenesis of H. influenzae
Important in young children as there is possible penetration of submucosa of nasopharynx
- H. influenza causes pharyngitis (preceding viral infection)
- Can cause sinusitis (epiglottiitis can be severe - asphyxia danger)
- Invasive disease
- Common bloodstream invasion
- Pneumonia, meningitis type b
Can cause pulmonary disease in adults with preceding viral infection/ chronic bronchitis
Features of C. diptheriae
Aerobic/ facultative anaerobic
Gram +ve diptheriods or coryneforms
Causes diphtheria
Spread by person-person contact in nasopharyngeal secretions (children susceptible)
What are the 3 types of C. diptheriae
Gravis
Intermedius
Mitis
