Bovine TB Flashcards
What is Tuberculosis?
contagious, bacterial zoonotic granulomatous disease
Caused by 3 types of mycobacterium
Mycobacterium avium (mostly birds) Mycobacterium africanum (Humans) Mycobacterium tuberculosis (mostly Human) Mycobacterium bovis (mostly bovine)
What is a granulomatous disease?
granuloma = organized collection of macrophages
One that contains lymphocytes, neutrophils, eosinophils, multinucleated giant cells, fibroblasts, and collagen (fibrosis)
what is significant about Mycobacterium Bovis?
No other organism has as great a host range as bovine TB
- it requires oxygen for growth
- it is v heat sensitive = why pasteurisation
- slow multiplication
- remains viable for time in cold weather
- or in warn, moist conditions e.g. stagnant water, faeces
Pathogenesis of M Boris
- primary route = inhalation
- 90% lesions in caudal lung lobe
- bacteria enter macrophages and reproduce
- lesions begin to form
- Spread is primarily through lymphatic channels, and occasionally haematogenous
- 70-80% of cattle cases show lesions in the retropharyngeal and broncho-mediastinal lymph nodes.
TB clinical signs
Weakness Weight loss-Progressive emaciation Chronic cough—low moist cough Loss of appetite Fluctuating pyrexia Mastitis Enlarged lymph nodes
Differential Diagnosis: Lung abscess Pleurisy/pericarditis 2nd to traumatic reticuloperitinitis Contagious pleuropneumonia – not UK Bovine Leukosis – not UK
What is a tubercle
white nodule usually 1mm-2cm in diameter within a lymph node or organ. Where found?
Most commonly found in the thoracic cavity
May be found in the liver or other major organs
What does the finding of gross lesions indicate?
Finding gross lesions is not conclusive evidence that the animal is infected.
What is the risk map of TB?
country has been divided into diff areas: Wales, Scotland and NI have different.
List and describe the diff areas we have in england
High Risk Areas
- High levels of bTB
- Breakdowns of long duration
- High reoccurrence
- Significant reservoir in wildlife (Badgers)
Edge Areas
- Designed to buffer
- Levels of bTB variable but higher than low risk areas
- Infection spreading north and east
- role of cattle and badgers uncertain
Low Risk Areas
- Low levels of bTB
- Breakdowns of relatively short duration
- No significant reservoir of infection in wild life
What increases number of TB cases?
- sie of herds
- management of herds
- inadequate tests to identify all
- Movement infected
- Wildlife reservoirs of M.bovis hard
Aim of TB control
- reduce spread - geographic
- protect public health
- Reduction disease incidence in cattle in high incidence areas
- eradicate it
What measures are out in place to control bovine tb?
- Surveillance
- Dealing with outbreak
- Disease prevention
- Controlling disease in badgers
How is TB surveillance?
- routine testine: Single intradermal comparative cervical test or gamma interferon test
- slaughterhouse surveillance
- Trade
Testing is carried out by Official Veterinarians or government approved TB testers and supervised by government-approved veterinarians. What are the six basic steps are:
- The animal is identified (by its ear tag) and its identification recorded.
- Two injection sites are selected in the middle third of the side of the neck, one above the other, separated by about 130mm. (if it is a small animal, the two sites will be on either side of the neck.)
- Hair is clipped around the sites to a radius of about 2 centimetres.
- A fold of skin at both sites is measured with calipers and the measurements recorded.
- Tuberculin is injected into the skin; the upper site is used for (usually) the avian tuberculin (or the left hand side on small calves).
- After 72 hours, the tester returns, confirms the animal identity, measures the same fold of skin at both sites and records the thickness of the skin fold.
inc 4mm vs avian = positive reactor
What results can the TB test have?
‘Clear’ (negative result)
‘Fail’ (reactor or positive result)
‘Inconclusive reactor’ (IR) greater reaction to bovine than avian tuberculin, but not enough to be classified as a reactor.
What is the gamma interferon test?
Animal’s blood is stimulated with avian and bovine TB in lab
WBC release cytokine IFNy and levels of it are measures
Advantages of gamma interferon test
Sensitivity = 90%
identify 9 out of 10 infected cattle
skin test = low sensitivity
Specificity = 96.5%
one false positive result for every 30 uninfected cattle tested.
Can be used at shorter intervals: don’t need to test at diff intervals, can be daily vs intradermal test can’t test again for 60 days
Can detect infected animals earlier
Quality depends on laboratory, not the field operator
Is generally less specific, but may be improved.
The test could reduce the duration of herd restriction
With flexible interpretation to allow for possible false positives
The test has also been used to resolve inconclusive reactors
