23. Disease Control Part II

Question 1

Disease control strategies (10):

Answer 1

-depopulation
-selective slaughter
-quarantine
-reduction of contract
-mass treatment
-mass immunization
-education
-environmental control
-applied ecology
-genetic improvement

Question 2

Depopulation:

Answer 2

-whole population (including non-infected) are scarified
-terminal stages of eradication programs
-‘blunt instrument’
-often accompanied by other procedures

Question 3

Slaughter in depopulation strategy:

Answer 3

-pre-emptive slaughter
>animals that may have been exposed to infection and at risk of developing disease

Question 4

When do you do depopulation?

Answer 4

-diagnostic test not easily applied or it is inaccurate
-population is inaccessible
-rapidly spreading disease
Ex. foot and mouth disease

Question 5

Other procedures that accompany depopulation:

Answer 5

-disinfection
-destruction of carcasses (burning or burial)
*reduce risk of transmission

Question 6

FMD in UK

Answer 6

-1400 vets mobilized
-2000 army troops
-1000 police
-15,000 vehicles
*tonnage of carcasses moved is GREATER than all ammunition moved by British troops in Gulf war
*2000 Olympic sizes swimming pool excavated
-1 mass burial site had 430,000 head capacity

Question 7

Selective slaughter:

Answer 7

-test and slaughter
-deliberate killing of minority of infected animals to protect healthy of majority
-involves a method of case finding
*more expensive as disease becomes rarer

Question 8

When would you use selective slaughter?

Answer 8

-early in disease outbreaks
-slowly spreading disease
Ex. brucellosis and TB

Question 9

Quarantine:

Answer 9

-isolation of animals that are either infected or suspected of being so
-movement restriction often used in combination with other control strategies
-national, regional, herd or within farm level
Ex. exclusion biosecurity, SPF barns

Question 10

Quarantine involves:

Answer 10

-restraining movement of exposed or infected animals or items that may be contaminated
-preventing entry of infected animals to premises or country

Question 11

Period of quarantine depends on:

Answer 11

-incubation period of the agent
-time taken for infection to be confirmed
-time taken for an animal to become non-infectious

Question 12

Reduction of contact:

Answer 12

-reduced or prevent contact between infected and non-infected animals
>movement restrictions
-separate in time (ex. different milking times)
-separate physically (calf hatches, rotational grazing for parasites)

Question 13

Mass treatment:

Answer 13

-treating all animals (sick and well)
-sometimes involves a diagnostic test

Question 14

When would you use mass treatment?

Answer 14

-combat disease occurring at very high prevalence
>depopulation and slaughter are not economical or viable
-need safe, cheap, effective therapy
-disease resistance problems?

Question 15

Examples of mass treatment:

Answer 15

-parasite control programs
-dry cow therapy
-‘metaphylaxis’ for brd in feedlot
-heartworm in dogs

Question 16

Mass immunization:

Answer 16

-creating immunity in population to limit spread and impact of disease
-successful for many veterinary diseases

Question 17

Mass immunization can:

Answer 17

-decrease prevalence to a point where other techniques can be used for eradication

Question 18

Problem with mass immunization:

Answer 18

-may interfere with screening tests
-difficult in wildlife populations

Question 19

Advantages with mass immunization:

Answer 19

-resistant individual can freely move
-don’t need frequent dosages

Question 20

Immunization considerations:

Answer 20

-importance of disease in question
-efficacy of vaccine
-duration of immunity
-accessibility of animal population
-dynamics of population
-cost of vaccine relative to other control strategies

Question 21

3 strategies for exotic disease control:

Answer 21

-ring vaccination
-barrier vaccination
-suppressive vaccination

Question 22

Ring vaccination:

Answer 22

-vaccinate them in the geographic area surrounding an outbreak to limit spread

Question 23

Barrier vaccination:

Answer 23

-vaccinate them in a particular zone to prevent spread into other countries

Question 24

Suppressive vaccination:

Answer 24

-vaccinating within an outbreak and in areas surrounding it

Question 25

Education:

Answer 25

-programs that educate the public
-often used in combination with other techniques
-hand washing, internal temp for meats
Ex. somatic cell count penalty programs, hydatid disease in New Zealand

Question 26

Environmental control:

Answer 26

-many public health programs began with environmental hygiene initiatives
-ventilation management, laminitis control, disinfection of fomites, mastitis control

Question 27

Applied ecology:

Answer 27

-use what is know about the ecology of a disease to prevent or control disease
-biological control mechanisms (‘niche filling’)
-may involve some form of vector control

Question 28

Applied ecology example:

Answer 28

-salmonella control in chicks in the poultry industry
-screwworm disease in southern US

Question 29

Genetic improvement:

Answer 29

-identify susceptibility to specific diseases
>remove them from breeding populations
-genetic indexes for sire selection
-breeding for disease resistance
-identify heterozygotes when disease is subclinical

Question 30

Scrapie susceptibility in sheep: genetic improvement example

Answer 30

-promote ARR gene: more resistant
-remove VQR gene: most susceptible

Question 31

Disease control example of bovine TB: (due to mycobacterium bovis)

Answer 31

-humans infected from raw milk or inhaling infective droplets
-federal reportable disease: CFIA
*long incubation and latent infections make control and detection difficult

Question 32

Canada bovine TB eradication program:

Answer 32

-started in 1924
-freedom in 1985
*several billion dollars

Question 33

Where is M. bovis found now?

Answer 33

-pockets of infection in wildlife in Canada, UK, USA and New Zealand
-common in Latin American and Caribbean countries
-endemic in regions of Africa and Asia

Question 34

Wildlife reservoirs of M. bovis:

Answer 34

-maintenance hosts and reservoirs for infection
-Badgers in UK
-possums in New Zealand
-Wild boar in Spain
-deer, elk, bison in NA

Question 35

In countries with active control programs for bovine TB:

Answer 35

-infected herds of cattle have low prevalence
>suggests low rates of cattle-cattle transmission

Question 36

Management activities that ‘likely’ contribute to control success in Riding Mountain NP:

Answer 36

-elk are reservoir
*barrier hay fences
*deer/elk density reduction
-remove of blood test positive elk/deer
-removal of bovine TB infected elk/deer
*adaptive management (research and annual surveillance results)

Question 37

Diagnostics for bovine TB:

Answer 37

-single intradermal tuberculin test
>caudal fold
>measure 72hours post injection
*imperfect specificity

Question 38

Imperfect specificity (97-99%) of single intradermal tuberculin test of bovine TB:

Answer 38

-false negatives occur (1-3%)
>due to cross reactions?
*also has poorer sensitivity (80-93%)
>more false negatives!

Question 39

What happens to reactors of bovine TB test?

Answer 39

-herd is quarantined
-animal is humanely slaughter
>If PM tests are positive=entire herd is humanely depopulated

Question 40

Investigation: CFIA will want to see

Answer 40

-management practices and biosecurity plan
-herd inventory records
-vet records
-records of animal movement
-site map of farm
-contract info for farm vet
*CFIA will begin trace in/trace out process

Question 41

Farm when positive PM TB test:

Answer 41

-farm is responsible for cleaning and disinfection process
-compensation process based on market value
-45 days after cleaning, quarantine can be lifted

Question 42

Alberta Outbreak example:

Answer 42

-slaughter plant found TB lesions
>direct herds
>trace out herds
>trace in herds
>buffer zone herds
*34,000 animals tested on 145 farms
>11,500 animals destroy and $39M compensation

Question 43

Lessons learned form Alberta outbreak:

Answer 43

-updated policies to deal with community pastures situations
-improve traceability of cattle movements
-lab support capacity was strained
-communication strategy was not ideal
*industry organizations played a key role (Ex. Alberta Beef Produces)