12.3: Myobacteria Flashcards
What is leading cause of death among HIV positive people in Africa?
- TB
- Immunosuppression leading to increased mortality
- 10% of aids patients who are infected develop disease each year
- Over 5 years if not treated for latent infection 50% develop disease
How many people in world are infected with TB?
- 1/3
- 9M new cases a year
Who are most of the people presenting with new cases of TB in america?
- Recent immigrants
- 70%
- Factors such as HIV
% of people infected with TB that develop disease in lifetime?
7 - 10%
How is it determined if you are infected with TB?
Positive skin test
of people in America INFECTED with TB?
- 10M
- Only 7 - 10% of these will develop disease in LIFETIME
How is TB transmitted?
- Human to human via aerosol drops
- Milk before it was pasteurized: GI TB
Who is likely to contract TB?
- Close contacts of infected person
- Immigrants
- Underserved
- IV Drug users
- Immunocompromised
Who is most likely to progress from infection to disease?
- HIV positive: low CD4 count
- Infected w/in last 2 years
- Babies / elderly
- IV drug use
How does TB travel in body?
- Inhaled and eventually moves to regional lymph node where it becomes bacteremic
- Allows TB to move to other parts of the body
- Usually not transmitted in blood born stage however can cause extrapulmonary TB
Negative effects of immune response to TB?
- Fibrosis and holes in lung
- Host defense causes the damage
Immune rxn with TB?
- Macs eat TB, digest and display in MHC to T cell
- T cell becomes primed or activated if has seen before
- Release cytokines that is protective and destructive
2 outcomes of primary TB?
- 90% have latent TB infection
2. 10% to active TB mostly people with AIDS
What is secondary TB?
- Reactivation of latent TB that spread during bacteremic phase
- 80% is in upper lung
- 15% of time it reactivates in extrapulmonary site
- Disease is waiting for opportunistic time to come out of latency when you are older or immune system is depressed
What does TB form on histology?
- Granulomas with giant cells surrounded by epithelial cells and central necrosis
What type of lung disease is TB referred to as?
Cavitary
How is TB diagnosed?
CXR with upper lung infiltrates and cavitation
Why is the hung back of notre dame hunched of?
Extrapulmonary TB of the spine
Does pulmonary TB present alongside extrapulmonary?
Not always
DDx in TB?
- Non TB mycobacterial infection
2. Fungal infection
What is PPD Skin Test?
- Intradermal inoculation of TB antigens
- If rxn results in lump in skin from CD4 cells, it means body has seen TB before
What is quantiferon assay?
- Similar to PPD but done in test tube
- If enough interferon gamma cytokine is produced it means body has seen TB
- INF gamma is what is causing the bump in the skin test
What is AFB?
- “Acid fast Bacilli” smear
- Performed on sputum to test for TB
What is NAAT?
“Nucleic acid amplification test”
- Take positive smear specimen and amplify in PRC like mechanism so you dont have to wait for culture to grow
