Tuberculosis

Question 1

Which bacterium causes TB?

Answer 1

mycobacterium tuberculosis

Question 2

What disease does M. Bovis cause?

Answer 2

Bovine TB in animals

Question 3

What is the reservoirs for M. Leprae?

Answer 3

humans
armadillos - in the lab

Question 4

What are some characteristics of the mycobacterium species?

Answer 4

1) mycolic acid virulence factor in cell walls - makes mycobacterium resistant to chemicals, stains and antibiotics, increases survival
2) intracellular survival
3) slow growing (15-22 hrs) and NOT fastidious

Question 5

What is the pathogenesis for M TB?

Answer 5

• it has 5 stages
• it replicates in macrophages when engulfed by them
• triggers T cell activation when APCs process the bacterial antigens and presents them on the cell surface via MHC II
  -this is recognised by T cells
• gamma interferon is released which helps macrophages limit spread of bacteria
• immune system forms granulomas (collection of immune cells surrounding infected area)

Question 6

What happens in a latent TB infection?

Answer 6

bacteria cease to grow and lesion calcifies

Question 7

What happens in an active TB infection?

Answer 7

-bacteria spreads to blood and organs
-bacteria is coughed up in sputum

Question 8

What is a ghon focus?

Answer 8

lesion found in lungs of individuals with M TB
localised area of inflammation
can undergo caseous necrosis over time

Question 9

What occurs to a healthy host in TB?

Answer 9

-cell mediated immunity prevents spread of TB
-TB remains latent
-however reactivation may occur

Question 10

What occurs to an immunocompromised host? (children, elderly,HIV patient/transplant patient)

Answer 10

pneumonia can develop
chronic inflammation

Question 11

What is secondary TB?

Answer 11

• reactivation of the initial infection
• associated with the impairment of the cell mediated immune response
• cheesy necrotic lesions develop which discharge contents into the bronchi -> contents of lesions are coughed up and become infective nuclei droplet

Question 12

What are the symptoms for TB?

Answer 12

lower respiratory tract infection: cough, sputum, weight loss, fatigue, fever

military TB where it spreads to other parts of the body: meningitis, septicaemia, kidney infection

Question 13

How would you diagnose TB?

Answer 13

• can do an x ray to identify ghon focus etc
  -tuberculin skin test/ Mantoux test

Question 14

What are some non culture techniques to detect tuberculosis?

Answer 14

Interferon Gamma Release Assay
PCR
Microscopy

Question 15

Which stain would you use on a microscope to identify TB?

Answer 15

ziehl-neelson stain/ fluorescent auramine stain

Question 16

What are the treatments for respiratory TB?

Answer 16

-isoniazid, rifampicin, pyrazinamide, ethambutol

Question 17

What are some side effects of the TB drugs?

Answer 17

• Isoniazid: hepatitis, peripheral neuropathy
• Rifampicin: hepatitis, stains bodily fluids orange
• pyrazinamide: hepatitis