Tuberculosis Flashcards
(25 cards)
Characteristics of Mycobacterium tuberculosis
- Acid fast bacillus
- mycolic acid within the cell wall retains the carbolfushcin stain - Obligate aerobe
- Slow growth rate (cultures held for 6-8 weeks before finalized)
Secondary infection of TB usually occurs where?
Apices of the lungs
What are the structures and properties that contribute to the pathogenesis of TB?
- Cell Wall: Many waxy-like substances that make the cell wall impermeable to many host defense systems
- Cord factor - Inhibits macrophage maturation and induces TNF-alpha release
- Sulfatides - inhibits phagolysosomal fusion
* allows MTB to grow inside the macrophage (protected from host immune system)
What protein may play a role in the inhibition of phagolysosomal fusion with a macrophage?
PknG
What is the most important determinant of whether overt TB disease will occur?
The adequacy of the host’s cell-mediated immune response
What cell types mount the response that leads to containment of the infections
- Th1 - response leads to granuloma formation and caseous necrosis
- Macrophages - once activated the secrete TNF and cytokines to recruit more monocytes
Risk Factors for TB
- Prison (crowded conditions)
- Immigrant from high burden country (Mexico)
- Malnourished
- Alcoholism
- Poverty
- AIDs
- Debilitating illness
- Elderly
- Certain diseases
Which disease increase the rick for TB
- DM
- Hodgkin lymphoma
- CKD
- Immunosuppression
5 RA (on TNF-alpha antagonists)
What percent of people infected with MTB actually develop the disease?
10%
Clinical manifestations of seconday/reactivated TB
- Insidious onset*
1. malaise
2. anorexia and wt loss
3. low-grade fever
4. SOB
5. night sweats
6. Cough productive of blood-streaked and/or purulent sputum
7. Pleuritic pain (Some ppl)
Clinical manifestations of progressive primary TB?
Presents like an acute bacterial pneumonia
- CXR with infiltrates or lobar consolidation
- hilar LAD
- pleural effusion
Clinical manifestations of Miliary/disseminated TB?
- Lymphoheme. disseminations usually follow primary TB infection
- CXR - looks like there a bunch of seeds all over it
- dyspnea and cough - Liver: RUQ pain w/ N/V
PTs with Miliary/disseminated TB are susceptible to what diseases?
- Meningitis
- Pott’s disease (vertebral osteomyelitits)
- GI (N/V and diarrhea)
- Urinary (Sterile pyuria, hematuria, proteinuria)
- Adrenal insufficiency, epididymitis, prostatiis
Dx of TB
- Acid Fast stain on sputum with a culture being done at same time
- If initial Acid fast is positive, PCR for rapid results
How to culture MTB?
Lowenstein-Jensen agar
- takes 3-6 weeks to grow
Liquid media shows results in as early as 2 weeks
Tx of secondary/primary pulmonary TB
If suspicious, begin tx:
- Initial 4 drug tx (RIPE)
1. Isoniazid
2. Rifampin
3. Pyrazinimide
4. Ethambutol - once susceptibility known and if susceptible. Stop ethambutol
- After 2 months of RIPE/RIP, can stop PZA, and contine with RI for 4-7 months to complete 6-9 month therapy
Tx of Miliary TB
Tx with RIPE for 9-12 months
- Isoniazid
- Rifampin
- Pyrazinimide
- Ethambutol
Why is a long course of therapy required for TB?
- Organism grows slowly
- There are metabolically inactive organisms within the lesion
- Organism is located intracellularly
- Caseous material blocks penetration by drugs
Multidrug resistant (MDR) TB is most commonly resistant to which drugs?
- Isoniazid
2. Rifampin
Describe the resistance in Extended drug resistant (XDR) TB
resistant to:
- Isoniazid
- Rifampin
- Flouroqinolone
- at least one addition drug
What is a risk factor for the development of TB resistance to Tx? How is it prevented?
Noncompliance
- Directly observed therapy (DOT)
All stages of HIV are associated with increased rick of TB, even with HAART. Why?
no immune response and so no bronchial damage and few acid fast bacilli in sputum
Dx of Latent TB
PPD: Purified protein derivative
- intradermal injection of tuberculin material which stimulates a delayed type hypersensitivity rxn
- causes induration within 48-72 hours in positive
- not perfect due to vaccines used in other countries and also due to nontuberculous mycobacterial infections
IGRA: interferon gamma release assay
- PT blood cells exposed to antigens from MTB and amount of IF-gamma released from cells is measure.
- NO false positive with BCG vac. or other organisms
Tx for latent TB
- Isoniazid for 9 months
- or- - Isoniazid and Rifapentine for 3 months
