Mycobacteria

Question 1

What is the background to mycobacteria?

Answer 1

• Non-motile
• non-spore forming
• aerobic or microaerophillic
• Gram Positive but hard to stain due to abundant lipid

Question 2

What does the thick layer of mycolic acids contribute to?

Answer 2

Environmental and antimicrobial resistance

Question 3

When is m.avium most commonly seen?

Answer 3

Most commonly causes mycobacteriosis in birds

Question 4

Where is m.bovis most commonly seen?

Answer 4

Persists in soil, remains infective for weeks
* high doses are required for oral transmission

Question 5

What is the normal pathogenesis of mycobacterium?

Answer 5

• Mycobacterium are phagocytosed by alveolar macrophages
• they prevent fusion of the phagosome with lysosomes
• they replicate and persist within macropahges

Question 6

What happens if mycobacteria is not phaocytosed immedietly?

Answer 6

• release of TNF-a, IL-12 and cytokines to recruit other macrophages and lymphocytes
• IL-12 drives a type I immune response

Question 7

What is the function of the tuberculoid granuloma?

Answer 7

• It prevents spread to other sites and other hosts
• Cell mediated response kills infected macrophages and forms the caseous centre

Question 8

What is the clinical presentation of mycobacterium bovis?

Answer 8

Most animals that are infected never develop clinical signs- they either eliminate or contain the bacteria

Question 9

How would you use an intradermal skin test to test for mycobacterium bovis?

Answer 9

Purified protein derivatives can produce delayed type hypersensitivity reactions in a sensitized animal

Question 10

What is the function of glycolipids in mycobacteria?

Answer 10

they induce a macrophage response and prevent lysosomal degredation

Question 11

What is tthe purpose of the granuloma formation during infection?

Answer 11

• helps contain the infection
• prevents spread

Question 12

What is the downside to the cell mediated response when the infection is large?

Answer 12

may cause extensive tissue damage

Question 13

What does the mycobacterium tubercle look like?

Answer 13

• Circumscribed, often encapsulated
• Pale, yellow-white nodule
• Granulomatous inflammation with central caseous necrosis
• large ones may liquefy
• Fibrosis increases over time

Question 14

What is the most common infection for humans?

Answer 14

M.Tuberculosis

Question 15

What is the most common route of infection for mycobacterium bovis?

Answer 15

Inhalation is the most common, this causes lesions in the lungs, airways and associated lymph nodes

Question 16

When does oral infection of mycobacterium bovis occur?

Answer 16

Occurs when there is coughing up and swallowing of sputum from infected lungs

Question 17

How does respiratory mycobacterium bovis occur?

Answer 17

• Tubercles spread into airways and release bacteria that can spread within the lung/ be coughed up and swallowed
• they can also erode into the pleura and spread in the pleural cavity

Question 18

What are the differences in lesions between cervids and cattle?

Answer 18

Cervids
* develop superficial lymphadenitis that drains to the skin surface
* Disease progresses faster
* they are less able to contain the infection and more susceptible
* suppurative inflammation is more prominent than caseous necrosis

Question 19

What do mycobacterium bovis lesions look like in carnivores?

Answer 19

• Discrete tubercles are uncommon
• instead they form granulation tissue

Question 20

What do mycobacterium bovis lesions look like in cats?

Answer 20

• nonhealing wounds with central necrosis
• low numbers of bacteria differentiate from feline leprosy

Question 21

What do mycobacterium bovis lesions look like in dogs?

Answer 21

rapid dissemination through bronchi, causing tuberculous bronchitis

Question 22

Why is M.bovis hard to culture?

Answer 22

Culture takes a long time due to slow growth (4-6 weeks)

Question 23

How are humans likely to be infected with M.bovis?

Answer 23

• Immunosuppression
• Contaminated Milk
• Aerosol or Wound Infections are also common

Question 24

What are the 4 routes of infection for m.bovis?

Answer 24

• Inhalation
• Oral Infection
• Transplacental
• Percutaneous

Question 25

Where are the vast majority of m.bovis respiratory lesions found?

Answer 25

mostly in the retropharyngeal, tracheobroncheol, mediastinal lymph nodes

Question 26

What do M.bovis lesions in the horse look like?

Answer 26

• Usually alimentary
• Tubercles can look more solid and resemble sarcomas

Question 27

What is the active method of managing m.bovis?

Answer 27

• Routine testing of clinically ‘normal’ animals
• Interferon gamma assay
• Test and slaughter schemes

Question 28

What is the passive method of managing m.bovis?

Answer 28

Examination of suspect infections

Question 29

What is the function of purified protein derivatives?

Answer 29

they can produce delayed type hypersensitivity reactions in a sensitised animal