Tuberculosis Flashcards
What are the four types of mycobacterium that can cause tuberculosis?
Myobacterium avium- birds mostly
Myobacterium africanum- humans
Mycobacterium tuberculosis- mostly human
Mycobacterium bovis- mostly bovine
What speceis can be infected by bovine TB?
Can be transmitted from livestock to humans, deer and other animals
What does mycobacterium bovis require for growth?
What can kill it?
How long can it remain viable for?
Require O2 for growth- very heat sensitive
Can be killed by a weak solution of common household bleach
Do not grow outside of host except in culture medium
Can remain viable for extended period of time in cold weather- lengthy survival in warm, moist, protected conditions
Stagnant water 18 days, faces 6-8 weeks
Describe the pathogenesis of TB?
- Inhalation is the primary route of infecitons, ingestion is also possible
- Only inhalation of 1-3 bacilli are enough to cause infection
- 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 retropharyneal and broncho-mediastinal lymph nodes
- Lesions cause caseous necrosis and liquefies and can spread to other organs
What are the clinical signs?
What are the DDXs?
- Weakness
- Weight loss- progressive emaciation
- Chronic cough- low moist
- Loss of appetite
- Fluctuating pyrexia
- Mastitis
- Enlarged lymph nodes
DDXs-
lung abscess, pericarditis, 2nd to traumatic reticuloperitinitis, contagious pleuropneumonia, bonce leukosis
What are the gross lesions caused?
Characteristic gross lesion of an animal infected it presence of ‘tubercles’ within the body
Tubuercles is a white nodule usually 1mm-2cm in diameter within a LN or organ
Most commonly in the thoracic cavity
May be found in the liver or other major organs
Which humans are at higher risk of TB?
Those working closely with livestock and people who drink unpasturised milk have greatest risk to exposure
What are the different ‘risk areas’ of bTB and what the difference?
High risk-
High levels of bTB, breakdowns of long duration, high reoccurence, significant reservoir in badgers
Edge areas-
levels of bTB variable but lower then high risk
infeciotn spreading north and east
role of badgers uncertain
Low risk areas-
low levels
breakdowns relatively short
no significant reservoir
What is the objective of TB control?
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
Eradicate bTB
What is the legislation around TB?
Requirement to notify suspected disease in bovine or deer
Requirment to notify suspected disease in a carcase of any bovine animals or other farmed or pet manual
Requirement to notify presence of the organism M.bovis which is identified by a lab
England bTB is statutorily controlled in England following, eradicate by 2038
Scotland bTB free since 2009
Wales- bTB subject to statutory control
How is bTB surveilled?
Routine testing-
active surveillance interval of 6 months, 1 or 4 years
UK compulsory- single intradermal comparative cervical test
Describe how routine testing is done and interpreted in the UK?
Testing-
- Animal identified with ear tag and its identification recorded
- Two injection sites- middle third of neck
- Hair clipped 2cm radius
- Fold of skin measured with calipers and recorded
- Tuberculin is injected into the skin- upper site avian, lower bovine
- After 72 hours tester returns and remeasures
Result-
Standard or severe depedning on disease history
Clear, fail or inconclusive
How else can TB be tested for other then use of tuberculin for routine?
When are they used?
Blood testing- gamma interferon
animals blood stimulated with avian and bovine tuberculosis in the lab
levels of IFNy measures
Sensitivity much higher then SICCT
Use- can be used at shorter intercals, can detect earlier, less specific, used for inconclusive
Antibody testing-
IDEXX antibody tests are taken within 10-30 days prior of a skin test
Can be useful for small numbers, can be used in UK at owners expense
How are cattle entering the food chain surveilled?
All cattle carcases are inspected by the FSA for suspect bovine TB lesions during commercial slaughter
