30 - Tuberculosis Flashcards
What is the most common mycobacteria that causes TB
M.tuberculosis
What are other mycobacteria that cause TB
M. bovis
M. africanum
M. microti
M. canetti
Name a mycobacteria that doesn’t cause TB
M.avium complex
How is TB spread
In the air via droplet nuclei
What does the probability that TB will be transmitted depend on
Infectiousness of person with TB
Environment in which exposure occurred
Length of exposure
Strength of the tubercule bacilli
What is the best way to stop transmission of TB
Isolate infectious persons
Treatment to infectious persons as soon as possible
How can you diagnose a latent TB infection
Mantoux with PPD or gamma interferon release assays
What year did TB control programs begin in
1992
What year was Streptomycin, Isoniazid an PAS DISCOVERED
o Streptomycin in 1943
o Isoniazid and PAS – 1943 and 1952
What is the treatment for drug sensitive TB
- Isoniazid, Rifampicin, Pyrazinamide + Ethambutol for 2 months
- Rifampicin and Isoniazid for 4 months
What does it mean if the TB is multi-drug resistant
Resistant to INH, RIF plus amikacin,kanamycin or capreomycin (injectable!agents) and resistance to any fluroquinolone
Features of mycobacterium
Slow growing
Prefer o2 rich env
Live inside cells
Clinical features TB
Fever Night sweats Weight loss Chronic cough chest pain
Why is TB hard to treat
1) Lipid rich cell wall - difficult for AB to enter cell
2) Slow growing and hide in macrophages
3) Resistant to penicillin
4) Not gram neg or gram positive cell wall
What occurs in primary TB
Mycobacteria –> in middle lung
Acute inflammatory response from neutrophils
Neutrophils –> phagocytose bacteria abut cannot destroy
Nearby cells and neutrophils die (caseous necrosis)
Some bacteria die
What is the ghon focus
Aggregation of macrophages around a necrotic centre
What type of immune response in primary tb
Type IV hypersensitivity
Structure of the caseous tissue
Caseous necrosis around macrophages around that (ghon focus) fused macrophages - langhan cells lymphocytes around the macrophages fibroblasts on the outside
What occurs in healthy individuals with primary tb
Ghon focus heals with deposits of collagen from fibroblasts
Ca salts are deposited in the collagen –> Ghon complex (ca on xray)
Secondary TB
o Bacteria remain alive in Ghon complex, immunosuppression/malnourishment –> bacteria escape and symptoms appear- REACTIVATION
How to diagnose TB
PCR Mantoux CXR Histology Sputum
Mantoux test pos in =
15mm or more = positive in healthy
10-15mm= positive in med risk ( drug users, homeless)
5-9mm= positive in HIV
Chest X-ray features
bilateral opacities, cavitations, calcification, hilar shadowing
Histology
caseous granulomas with Langerhans giant cells on h and E stain
Microbiology
Lowenstein Jensen medium – 4/6wks and sensitivity) + STAINING zielh neilson (red) or more sensitive auramine stain (Orange under fluorescent microscope) reveals AFB** inside macrophages
Pyrazinamide
inhibits the enzyme fatty acid synthase (FAS) which is required by the TB bacterium to synthesise fatty acids.
SE - gout
Ethambutol
bacteriostatic, It prevents the formation of the cell wall
SE - vision changes
Rifampicin
antibiotic which inhibits bacterial DNA-dependent RNA polymerase
SE =- Red-orange metabolites + induces liver enzymes
Isoniazid
prevents synthesis of mycolic acid, component of the TB bacterial cell wall.
SE - Neuropathy, hepatitis
