What Mycobacterium strains cause TB?
- Avium
- Tuberculosis
- Bovis
What are the characteristic features of Mycobacterium bovis?
- Aerophilic
- Heat sensitive
- Sensitive to bleach (1:9)
- Slow growth rate
- Obligatory hosts
- Remain viable in cold conditions
- Likes warm, moist, protected environments - stagnant water, faeces
Outline the pathogenesis of M. bovis.
- Inhalation/ ingestion
- Spread through lymphatic channels & haematogenously
- Reaches lungs and reproduces in macrophages
- Cause caseous necrosis
- Bacteria stop growing and lesion calcifies (may reactivate if immunosupressed)
- Lesion liquifies - spreads = death
- Bacteria coughed up in sputum
What inhalation dose of M. bovis is required to cause infection?
1-3 bacilli
Outline the clinical signs associated with bTB.
- Progressive wt loss
- Chronic low moist cough
- Anorexia
- Pyrexia - fluctuates
- Mastitis
What Ddx. should be explored with c/s of TB?
- Pulmonary abscess
- Pleurisy
- Pericarditis
- 2nd to traumatic reticulopericarditis
- Contagious pleuropneumonia
- Bovine Leukosis
Tubercle.
Describe
- 1-2cm
- White nodular lesion
- Focal/multifocal
- Within lymphnodes or organs (thorax, liver + others)
Miliary type lesions
Small, multifocal/ coelescing white nodules in pleura and thoracic cavity
Which group of people are considered at zoonotic risk from bTB?
Immunocompromised
Consuming unpasteurised milk
Why are badgers considered continuous shedders of bTB?
They have unencapsulated granulomatous lesions so shed regularly
In which species is TB a notifiable disease?
Cattle
Deer
Tuberculin test
A comparative intradermal cervical test - uses bovine and avium tuberculosis
After how long are tuberculin tests reassessed?
72 hrs
What three results are possible from the tuberculin test?
- Negative - no action taken if whole herd is clear
- Suspect/ inconclusive - B 2-4mm > A
- Euthanase
- Retest after 60 days
- Reactor - B>A 5mm
- Slaughter, isolate, PM, milk discard
Which types of herd are considered high public health risk?
Bottling unpasteurised milk
Supplying raw milk to manufacturers of unpasteurised dairy products
How often do high risk herds require testing?
Annually
What cattle control measures should be employed if TB is confirmed in a herd?
- Remove infected animals
- Movement resitrictions
- Short interval testing
- Minimum 60 days
- 2 consecutive tests required
- Gamma interferon testing - earlier detection
- Cattle tracing
- Testing neighbouring farms
