Lecture 11- Tuberculosis

Question 1

symptoms of TB

Answer 1

abnormal X-ray with a cavity within the area of confluent shadowing. “cotton wool” appearance in lung on x ray is puss.

Question 2

TB pandemic

Answer 2

1/3 of world population is infected

• 1.5 million have clinical disease at any one time
• 96% of TB death occurs in the developing world
• most have HIV/TB co infection.

Question 3

classification of mycobacteria

Answer 3

1. mycobacterium tuberculosis
2. non tuberculosis mycobacteria
   - rapid growing
   - non rapid
   - other

Question 4

How do you catch TB?

Answer 4

droplet and airborne transmission

cutaneous
gastro-intestinal tract (M.bovine)
these two don’t happen anymore.

Question 5

risk for transmission- recipient factors

Answer 5

household contact with TB-flatmate/spouse
age-children at greatest risk
immune suppressed-HIV/alcohol
institutional care-prison
healthcare workers

Question 6

risk for transmission-host factors

Answer 6

pulmonary TB
acid-fast bacilli visible in stains of sputum
cavitation visible on chest x ray
cough and failing to cover mouth
delay in diagnosis

Question 7

How should be diagnose TB

Answer 7

suspicion
chest x ray
sputum specimens
TB PCR
TB culture

Question 8

Ziehl-Neelsen stain

Answer 8

1. smear specimen on slide
2. apply carbol-fuschin stain
3. apply heat
4. wash with HCL

mycobacteria retain the stain

Question 9

Tests to determine latent TB

Answer 9

Interferron Gamma Release Assay
whole blood including white cells in test tube
add a mitogen to make lymphocytes proliferate-they release interferon gamma
add tb antigens-sensitised lymphocytes will release interferon gamma and proliferate- this person has been exposed to tb in the past

TB protein given intradermally. dendritic cells process antigen and present them to T cell. review in 72 hours- if an inflammatory lump is present the person is hypersensitive to TB antigen indicating that have the virus.
not specific for TB (other mycobacteria also)
some people are anergic (don’t respond)
takes 3 days so many don’t come back to have it read
interpretation is difficult (negative in HIV infected person is different from negative in non HIV infected person.

Question 10

TB treatment

Answer 10

usual targets for antibiotics don’t work on TB
eg. penicillin targets transpeptidase but TB’s cell wall doesn’t rely on transpeptidase.

prevent transmission

1. wear respirator masks
2. isolation
3. rifampicin (RNA target)- needed to kill a dormant bacteria and provide cure
4. isoniazid(cell wall-myopic acid target)- rapidly bactericidal against dividing bacteria
5. pyrazinamide- sterilises rapidly dividing bacteria-gets into granuloma well
6. ethambutol-not very active but helps to protect against development of drug resistance

combinations of at least 3 active first line drugs for many months are required to cure TB
the shortest duration of therapy is 6 months for pulmonary TB where all doses are taken and the organism is susceptible. disease of other sites takes longer.