Bovine Tuberculosis Flashcards
Who are the natural hosts of M.tuberculosis
Humans
• Can be transmitted to pigs, cattle, cats and dogs
Describe the conditions/sensitivities of growth for mycobacterium bovis
- Require oxygen for growth
- Very heat sensitive
- Can be killed by a weak solution of common household bleach
- Mycobacteria do not grow outside of a host except in cultured media
- Can remain viable for extended periods of time in cold weather
- Lengthy survival in warm, moist, protected conditions
What is the primary route of infection for Mycobacterium bovis?
Inhalation
- Only inhalation 1-3 bacilli are enough to cause infection
Where are lesions due to Mycobacterium bovis located/spread?
- 90% of lesions are in the caudal lung lobes
- Spread is primarily through lymphatic channels, and occasionally haematogenous
- 70-80% of cattle cases show lesions in the retropharyngeal and broncho-mediastinal lymph nodes
What are the clinical signs of Mycobacterium bovis?
- Weakness
- Weight loss: progressive emaciation
- Chronic cough: low moist cough
- Loss of appetite
- Fluctuating pyrexia
- Mastitis
- Enlarged lymph nodes
What are the 3 differential diagnosis for Mycobacterium bovis?
- Lung abscess
- Pleurisy/pericarditis
- 2nd to traumatic reticuloperitinitis
Describe the gross lesions of mycobacterium bovis
- Characteristic gross lesion of an animal infected with bovine TB is the presence of “tubercles” within the body
- A tubercle is a white nodule usually 1mm-2cm in diameter within a lymph node or organ
- Most commonly found in the thoracic cavity
- May be found in the liver or other major organs
- Finding gross lesions is not conclusive evidence that the animal is infected
In which cells do M.bovis reproduce?
Macrophages
What are miliary pathological lesions?
Small nodules spread throughout the pleura
Which factors are contributing to the long term trend of M.bovis infections?
- Herds are getting bigger over time making management and identification more difficult
- Inadequate tests to identify all infected cattle.
- Movements of infected cattle
- Wildlife reservoir of M.bovis infected animals especially badgers
What are the aims of controlling Tuberculosis?
- Protect public health
- Slow down and prevent the geographic spread of bTB to areas currently free of disease
- Achieve a sustained reduction in disease incidence in cattle in high incidence areas.
- Eradicate bovine tuberculosis
Describe notification of M.bovis
- Requirement to notify suspected disease in bovines or deer
- Requirement to notify suspected disease in a carcase of any bovine animal or other farmed or pet mammal
- Requirement to notify presence of the organism M. bovis which is identified by a laboratory examination of a sample taken from any mammal (except man) or from the carcase, products or surroundings of any such mammal
Describe routine testing for M.bovis
- Active surveillance through systematic field testing of OTF herds at a predefined interval of six months, one or four years
UK Compulsory tuberculin herd testing:
• using the single intradermal comparative cervical test. (SICCT) M. avium and M. bovis tuberculin in two separate sites and followed for 72 hours
• mainly by private veterinarians, contracted to the Government - Elsewhere Single intradermal test – most widely used. Based on tuberculin protein from cultures of M. tuberculosis and M. bovis
Who inspects carcasses for suspected bovine TB lesions during commercial slaughter
Food standards agency
Describe the 6 basic steps in testing for mycobacterium bovis
- 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
- 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 the avian tuberculin
- 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.
How is the TB test result interpreted?
Either the ‘Standard’ or the ‘Severe’ interpretation, depending on the disease history of the herd, or other circumstances.
Based on the difference in skin thickness measurements and test interpretation the test can have one of three results.
What are the 3 possible TB test results?
- ‘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 another form of TB test?
Blood testing: Gamma interferon test
- Instead of injecting tuberculin’s into the skin, the animals blood is stimulated with avian and bovine tuberculin’s in the lab
Compare the specificity and sensitivity of the SICCT and the IFG Tests
SICCT = 50-80% sensitivity and 99.98 specificity
IFG = 90% sensitivity and 96.5% specificity
- Sensitivity = the test may miss some infected animals
- Specificity = false positives
What are the uses/pros of the gamma interferon test?
Can be used at shorter intervals: with the intradermal test, once you have tested the animals you cant retest for another 60 days because its likely that stimulation from the previous test will give you a positive result
- Can detect infected animals earlier
- Is generally less specific, but may be improved.
- The test could reduce the duration of herd restriction
What is a TB breakdown?
When a herd loses its officially TB free (OTF) status due to bovine TB being suspected or confirmed
What are the principle points of a TB breakdown?
- One or more animals testing positive to a TB skin test (reactors)
- One of more animals having two consecutive inconclusive skin test results
- One or more animals testing positive to a private interferon gamma blood test
- One or more clinical cases
- One or more report cases: lesions of TB are found in the carcass of an animals
- One or more slaughterhouse cases
Describe movement restrictions
- Cattle movement restrictions are applied immediately when bovine TB is suspected through testing or slaughterhouse inspection,
- Livestock movement restrictions imposed immediately a herd’s routine test becomes overdue as the disease status is unknown
What are the steps in dealing with a TB outbreak?
- Movement restrictions
- Slaughter of reactors
- Short interval testing
- Testing neighbouring herd(s) Risk based
Describe short interval testing
- Bovine TB breakdown herds undergo a series of tuberculin skin tests, at minimum intervals of 60 days. Depending on post-mortem findings, breakdown herds must have one or two consecutive clear tests before they regain their bovine TB free status.
- Skin testing may also be supplemented by gamma interferon blood testing in some circumstances
How is TB spread prevented?
Pre-movement and post-movement TB testing is in place to help the reduce the spread of TB from the movement of cattle especially to areas that are free of disease.
Describe some enhanced biosecurity and husbandry practices by cattle owners to help prevent TB
- Stop badgers from entering cattle housing
- block gaps and use sheer sides with no footholds can stop badgers entering buildings
- If you cannot stop visits to feed stores consider storing feed in metal, lidded, feed bins
What are the options for controlling transmission of bovine TB from badgers to cattle?
Culling
Vaccination
When are the closed badger culling seasons?
- Controlled shooting – 1 February to 31 May
- Cage-trapping and shooting – 1 December to 31 May
- Cage-trapping and vaccination – 1 December to 30 April
What are the aims of badger vaccination
- Reduce transmission of TB between badgers
- Reduce transmission of TB from badgers to cattle
- Reduce prevalence in badger populations and the severity and shedding of bacteria from infected badgers
- Achieve herd immunity
