Mycobacterial Disease Flashcards
What can you divide mycobacteria into?
Mycobacteria are divided into slow-growing and rapid-growing mycobacteria
- <7 days = rapid grower
- >7 days = slow grower
- Leprosy not grouped as cannot be grown
types of mycobacterium
Mycobacterium microbiology
- Non-motile rod-shaped bacteria (structurally gram +ve)
- Relatively slow growing compared to other bacteria
- Long-chain fatty (mycolic) acids, complex waxes and glycoproteins in cell wall
- Structural rigidity
- Complete Freund’s adjuvant
- Staining characteristics
- Acid-alcohol fast bacilli (AAFBs)
- Staining: Auramine (screening), Z-N (diagnosis
Mycolic acid provides staining properties and alcohol resistant
NTB Mycobacterium features
- Ubiquitous
- Environmental (i.e. water and soils)
- Atypical
- Spectrum of pathogenicity (majority are not pathogenic to humans) and may be found colonising (not infecting)
- Not transmitted person-to-person
- Commonly resistant to the usual anti-TB therapy
Slow growing NTM
Rapid-growing NTM
NTM epidemiology
- Ontario (MAI/C incidence high), Netherlands (incidence NTM increasing over MTB)
RFs for NTM
age
underlying lung disease
NTM Diagnosis
- BTS Guidelines 2017
- American Thoracic Society Guidelines
- Combines clinical findings with microbiology findings (blood culture, bronchoalveolar lavage, biopsy)
- Exclude other diagnoses
NTM Tx
2 types of mycobacterium leprae
Paucibacillary tuberculoid
- Few skin lesions + less joint infiltration
- Robust T cell response
Multibacillary lepromatous
- Abundance of bacilli
- Multiple skin lesions + joint infiltration
- Poor T cell response
MTB: epidemiology, disease states, MTB complex, transmission, prevention
Natural history of MTB (primary, latent, reactivation)
post-primary TB: Risk factors, and clinical presentations
-
Post-Primary TB = a reactivation or exogenous re-infection:
- Happens >5 years after initial infection
- 5-10% lifetime risk
- Risk Factors for Reactivation:
- Immunosuppression
- Chronic alcohol excess
- Malnutrition
- Ageing
Clinical Presentation:
- Pulmonary or extra-pulmonary
- Host immune response shapes the clinical outcome – SEE ABOVE
MTB diagnosis
Pulmonary vs extra-pulmonary disease
MTB: clinical approach, RFs, presentation
MTB Ix’s
MTB Smear → culture and staining:
- Sputum (60% sensitivity, but increases with additional samples → hence, 3 samples)
- Gastric aspirated in children
- Rapid
- Operator-dependent
Tx of MTB
Side effects of RIPE
TB adherence
- Direct observation therapy / DOTS
- Video observed therapy / VOTS
Types of resistance and cause
Multi-Drug Resistant (MDR) → resistant to rifampicin and isoniazid
Extremely Drug Resistant (XDR) → resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable
- Due to spontaneous mutation + inadequate treatment
- They require a 4/5-drug regimen of longer duration (9-12m)
- Quinolones + aminoglycosides + para-aminosalicylic acid (PAS) + cycloserine + ethionamide
- Current WHO recommendations state that 7 drugs should be used for 9-12 months
- Risks side effects for longer…
when does risk of drug-resistant TB increase?
previous TB tx
known contact with MDR TB
HIV+
Failure to respond to conventional TB
HIV and TB co-infection: diagnostic and tx challenges
Diagnostic Challenges:
- Clinical presentation is less likely to be classical with symptoms and signs absent if low CD4+
- CXR may be normal (more likely to have extra-pulmonary manifestations)
- Smear microscopy and culture is less sensitive
- Tuberculin skin test is more likely to be negative
- Low sensitivity of IGRAs
Treatment Challenges:
- Timing of treatment initiation
- Drug interactions
- Overlapping toxicity
- Duration of treatment (adherence)
- Healthcare resources
