Mycobacterial Disease Flashcards
Which bacteria cause TB?
- M. tuberculosis
- M. bovis (1% of human cases) in cattle
- More rare sub-species
What are the different stages of a TB infectiton?
Which ones are usually symptomatic?
Usually Reactivation of Latent TB with trigger (immunosuppression, idiopathic) becomes symptomatic
More rarely primary TB can also be symptomatic
How is TB generally transmitted?
Human to Human Aerosole tranmission (with active pulmnoary/laryngeal TB - other forms of TB (e.g. bone obv, not infectious))
Give an example of another Mycobacteria / Acid Fact Bacilli positive bacteria that does not cause TB?
- e.g. M. chelonae (skin infections)
- M. avium
- others
What is Latent TB?
A TB infection, that only causes one acute infection period (2-3 weeks of B symptoms + cough), with no active TB afterwards
What is the worldwide prevalence of Latent TB?
1/4 - 1/3 of population
What is the progression rate of Latent TB into active TB?
When does this usually develop?
How does the likelihood change with active HIV infection?
10%
Usually incubation period 3-9 months, usually <2 years
With active HIV infection: 30-50%
How is latent TB diagnosed?
Mantoux with PPD (purified protein derivate) –> shows exposure (positive in latent, active, BCG)
or gamma interferon release assays (IGRA) –> Shows Exposure (active or latent, negative in BCG)
What is the current treatment Regime for drug-senstive TB?
Give 4 (RIPE) for 2 months, and then 2 of them for 4 months (depending on Culture and Sensitivity - usually P and E stopped due to bigger side-effect profile) (RIP available as combinations Rifater)
○ Pyrazinamide and Ethambutol - 2 months
○ Rifampicin and Isoniazid - 6 months ("Rifinan")
Depending on sensitivity results: may decrease down to 3 drugs
With what 5 Methods can TB be diagnosed?
- Microscopy ZN stain (30min)
- Microscopic Auramine stain (20-30min)
- Xpert MTTB/ RIF (PCR) (2h)
- Liquid cultures (2 weeks)
- Solid Cultures (4-6 weeks)
What is Multi-drug resistant TB?
TB resistance to Rifampacin and Isaniazid
How is Muldti drug resistance TB diagnosed?
Now with WGS (Whole genome sequencing) DNA sequencing of Culture TB to test for resistance gene (Rifampacin most important).
Future looking into WGS of sputum direcly
How good is rapid TB diganostics compared to cultures
What is the gold-standard diagnosis of TB?
75% of microscopy negative cultures will be true positive on rapid diagnostic tests
Culture on Lowenstein-Jensen medium for 6wks (gold standard)→ acid fast bacilli seen + positive stain of Zhiel Nielson on sputum
Which factors influcence likelihood of TB transmission?
- Infectiousness of person with TB disease
- Environment in which exposure occurred
- Length of exposure
- Virulence (strength) of the tubercle bacilli
How is latent TB generally managed?
Overall aim: prevent active TB
1. Diagnosis
2. Chemoprophylaxis
Offer different drug regimes, depending on patient but usually
- 3 months of isoniazid (with pyridoxine) and rifampicin or
- 6 months of isoniazid (with pyridoxine)
What is the epidemiology of Multi-drug resistant TB?
common, depending on country.
3 countries account for 50% of worldwide MDR/RR TB
1. India (24%)
2. China (13%)
3. Russia (10%)
(Most of UK/ EEA drug sensitive)
What is the efficacy of the BCG vaccine?
What is a contraindication of giving the BCG vaccine?
About 70%
Immunosuppression is contra-indication, as it is a life-attenuated vaccine)
The classical presentation of TB is pulmonary Tb with constitutional symptoms, cough (+/- haemoptysis) and upper lobe caviation.
Can you name 2 others?
Overall more common with immunosuppression
- Spinal (Pott’s disease): back pain, discitis, vertebral destruction, iliopsoas abscess
- Milliary TB: disseminated haematogenous spread (seen on CXR)
+ Many more (can presen pretty much anywhere)
What is the most common side-effects of each of the RIPE drugs?
- Rifampacin - orange secretions
- Isoniazid: peripheral neuropathy
- Pyrazinamide: hepatotoxic
- ethambutol – optic neuritis
What pathogen is Leprosy caused by?
What is the current epidemiology?
Caused by Mycobacterium Leprae (non-tuberculous Mycobacterium)
Now only worldwide 150 new cases annually, most in US
What is the clinical presentation of Leprosy?
Skin depigmentation
nodules, trophic ulcers
nerve thickening
Lifelong illness, most disability due to nerve damage
What disease is caused by Mycobacterium Avium-Intracellulare complex?
What is the usual patien group involved?
Example of a non-tuberculous causing Mycobacterium
disseminated infection in immunocompromised; resembles TB if underlying lung disease
A fish lover with 6 aqauriums is presenting with a slow-growing bump on his left hand. Biopsy of the lesion reveals positive Zhiel-Nielson stain. What is the mst likely diagnosis?
Infection with Mycobacerium Marinarum –> causing Fish-tank granuloma
(Non-tuberculosis causing Mycobacerium)
