TB

Question 1

Name the vaccine used to protect against Mycobacterium Tuberculosis (½)

Answer 1

Bacille Calmette Guerin, BCG

Question 2

This vaccine is derived from an organism. Describe the nature of the organism in this vaccine (1)

Answer 2

Live attenuated strain of Mycobacterium [bovis]

Question 3

How effective is the vaccine at preventing TB? (2)

Answer 3

Does not protect against pulmonary TB. Protects against disseminated forms of TB, such as Miliary TB and TB meningitis

Question 4

What type of hypersensitivity response does the tuberculin skin test measure? (½)

Answer 4

Delayed type hypersensitivity, type IV

Question 5

Name three (3) factors in the case that may have predisposed Sipho to getting TB (1½)

Answer 5

Overcrowding, Contact with uncle, Possibly no BCG vaccination (no RTH card, thus no proof)

Question 6

Name the drugs used to treat TB in an adult (Sipho’s uncle) (2 – ½ each)

Answer 6

Rifampicin, Isoniazid (INH), Ethambutol, Pyrazinamide (PZA)

Question 7

In light of the history of Sipho’s uncle having TB, Sipho’s mother was asked to bring her two other children to the clinic for evaluation – particularly Thandi, the three-year-old.

Explain why the children have been brought to the clinic, and what intervention (if any) should be considered (3)

Answer 7

Childhood contacts (particularly those under 5 y/o) should be evaluated to determine whether they have any features of TB. If they do not have active TB, they should be given chemoprophylaxis in the form of INH for 6 months.

Question 8

Apart from microscopy, name two other methods that can be used to confirm a diagnosis of tuberculosis and list one advantage and one disadvantage of each method (3)

Answer 8

PCR/ Molecular/ GeneXpert

• Expensive, may require lab infrastructure
• Quick, more sensitive than microscopy
• Less sensitive than culture
• GeneXpert very easy to do – less operator dependent

Culture

• Slow, requires lab infrastructure, also expensive
• Most sensitive method currently available
• Urine antigen detection (not widely used as yet, but preliminary evidence suggests it is very specific, although insensitive)
• Quick, relatively cheap, no lab infrastructure required
• Insensitive
• (NOT IGRA – doesn’t differentiate between active and latent)

Question 9

Name the primary route of transmission of M. tuberculosis (½)

Answer 9

Airborne – respiratory droplet nuclei

Question 10

Mr Gammies had a BCG vaccine as a child. (Total = 4)
What protection did this provide? (2)
Why has he nevertheless developed tuberculosis of his spine? (1)

Answer 10

BCG protection is only partial and is most effective in preventing childhood TB meningitis and disseminated TB. Protection wanes with age and there is little protection for adult TB.

Question 11

If material could be obtained at surgery from the vertebral body, what quick tests could be performed in the microbiology laboratory to establish the diagnosis? (½x2 =1)

Answer 11

Microscopy of a stained smear (½) Ziehl-Neelsen or Auramine (½)