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
What is a TB breakdown?
What are the 6 different causes?
A TB breakdown is when a herd loses its officially TB free status (OTF) due to bovine TB being suspected or confirmed
6 Different Causes:
- One or more animals testing positive to a TB skin test- reactors
- One or more animals having inconclusive skin test results- 2xIRs
- One or more animal testing positive to a private IFNy blood test- reactors
- One or more clinical cases- possible signs of TB
- One or more report cases- lesion of TB found in carcase
- One or more slaughterhouse case
What happens following a TB breakdown?
- Isolation of reactors
- Movement restrictors
- Reactor removed and slaughtered
- Cleaning and disinfection of isolation areas
- Short interval skin testin (day 60)
- If clear OTF status restored
Why is PM insensitive for conformation?
What is short interval testing?
Positive but NVL animals are usually early stage to see anything in organs, small lesions can be missed at the slaughter house, genuine false positives
Short interval testing- minimum of 60 days depending on PM findings- two consecutive clear tests before OTF
Skin may be supplemented by IFNy test
IFNy test compulsory for every new leions or culture positibe TB breakdown in the low incidence areas/Scotland
How is TB and spread prevented?
Pre-movement and post-movement TB testing is inplace
Pre-movement testing- aims to slowdown/prevent spread
Pre and post in Scotland, pre in England and Wales
Enhanced biosecurity- feed store, reduce risk
What are the options for controlling transmission of TB from badgers to cattle?
When is badger culling allowed?
Culling or vaccination
Badger culling- permitted under licence
controlled shooting- 1feb- 31 may
cage-trapping and shooting- 1 dec-31 may
cage trapping and vax 1 dec- 30 april
What are the types of licence for badger control?
A badger control licence- where culling to take place for first time in high risk
A low risk control licence- culling to take plasce in low risk area- evidence that infection is present in badgers with infection in cattle
Supplementary control licence- culling is to take place to prevent recovery of population
What is the aim of badger vaccination?
Reduce transmittion between badgers and cattle
Reduce prevalence in badger populations and severity of shedding
Can be vet or trained non-vet
May not fully protect badgers- may not benefit already infected badgers
