Bovine tuberculosis control Flashcards

1
Q

What bacteria causes Bovine TB?

A

Mycobacterium bovis

(Maybe M. Orygis in India)

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2
Q

What is the cost to the global economy of bovine TB?

A

$3 billion

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3
Q

What animals can bovine TB infect?

A

Includes cattle, humans, badgers, sheep, camelids, wild boar, deer etc.

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4
Q

What are the key features of a bovine TB infection?

A

Pulmonary disease, with involvement of draining lymph nodes

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5
Q

Transmission routes of bovine TB between cattle

A

Ill defined

Nasal secretions (direct contact)
Aerosols

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6
Q

Diagnosis of bovine TB in cattle

A

Routine slaughterhouse surveillance

Routine testing of cattle and slaughter of diagnosed animals

Pre-movement testing of cattle

Detailed follow up of herds that have had infections

Ante-mortem diagnostics (insensitive)

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7
Q

Routine bovine TB testing of cattle

A

Six monthly or annual testing of all animals in high incidence areas, four yearly testing of breeding stock in low incidence areas

Pre-movement testing of cattle being moved from or in high incidence areas

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8
Q

Ante-mortem diagnostic techniques for bovine TB

A

Delayed-type hypersensitivity testing
- insensitive but specific

Gamma interferon assay improves sensitivty

Culture of M. bovis
- gold standard but insensitive

Antibody tests
- poor sensitivity

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9
Q

Delayed-type hypersensitivity reaction (cell-mediated immune response) to M. Bovis extract

A

Single intradermal comparative cervical tuberculin test -SICCT

Sensitivity 50-95%

Specificity 99.98%

Gamma interferon assay improves sensitivity but relatively poor specificity (and cost) makes test unsuitable for routine surveillance. Now widely used in badger cull areas and in low risk area of England. Can lead to farms becoming classified as infected when they are not.

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10
Q

Antibody tests for Bovine TB

A

Poor sensitivity

+problems with cross-reactions, disease status, etc.

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11
Q

Epidemiology of bovine TB in the UK

A

Very heterogeneous across UK

Just cattle to cattle transmission in low incidence / ‘free’ Scotland and N England

Burden of wildlife challenge in SW England and parts of Wales

Badgers infection estimated to be associated with 50% of herd breakdowns in ‘trial’ areas (substantial cattle to cattle cycling within this figure)

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12
Q

Most commonly affected organs in bovine TB

A

Lungs

Pleura

Bronch-mediastinal LNs

Head LNs

Udder

Supra-mammary LNs

Liver

Hepatic LNs

Mesenteric LNs

Skin TB

Other (including kidney/spleen)

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13
Q

WHT and RHT in bovine TB testing

A

Whole herd test and Reactor herd test

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14
Q

Results of badger culling

A

Reduced incidence by ~25% in culled regions

But incidence increased by ~12% in peripheral regions due to perturbation

Led to suggestion that average rate of reduction in average sized culling region is 16%

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15
Q

Cattle vaccination for bovine TB

A

Massively hampered by need to continue testing vaccinated animals

Lack of available DIVA

Cost-benefit analysis suggests that it might not be feasible to get farmer uptake

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16
Q

Recurrence of bovine TB

A

50% of herds infected have breakdown in previous 3 years, 40% within 2 years

Could be due to
§ Persistence in cattle
§ Reintroduction from wildlife
§ Reintroduction from cattle movement

30% have ‘prolonged’ breakdowns

Up to 20% may have persistent infection when cleared, not all will lead to breakdowns

Most recurrence is due to reintroduction

17
Q

Annual herd prevalence of bovine TB

A

16-18% in current annual testing areas - mostly recurrently infected farms

18
Q

What % of bovine TB is detected in slaughterhouses?

A

22%

19
Q

Vaccination of cattle for bovine TB

A

BCG- attenuated strain of M. Bovis

Less efficient than tuberculin testing

Experimentally: significant protection of calves neonatally vaccinated at 12 months

No significant protection at 24 months

Vaccination with BCG sensitises animals to tuberculin

Licensed for use in badgers -reduced risk of infection, not yet demonstrated to have an impact on the incidence of disease in cattle

Subject to complex rules with EC. Currently illegal, but legislation could be changed.
Unclear quite how much vaccination would interfere with testing

20
Q

Edge area measures

A

Enhanced breakdown follow-ups/surveillance

To prevent geographic expansion of infected areas

Enhanced cattle control measures

21
Q

Badger culling

A

Conclusion of ISG in 2006 said no meaningful contribution but was not really accepted

Estimation that culling in largish areas would result in 16% reduction overall

Anything that can do even this is a method that needs to be considered

However doesn’t mean you need to accept it on a ethical basis

Policy is still that intensive culling should be phased out eventually