Disease Control Strategies at the Population Level

Question 1

Disease Eradication

Answer 1

• refers to regional elimination of an infectious disease (Ex. Brucellosis, hog cholera, FMD)
• very few diseases have actually been eradicated (Human Smallpox, Rhinderpest)

Question 2

Purpose of disease eradication

Answer 2

To reduce prevalence to level that transmission does not occur OR to the level that the disease is no longer a major health problem

** Often time limited campaign

Question 3

3 things needed for disease eradication

Answer 3

1. effective intervention that can interrupt transmission of an agent
2. practical diagnostic tools with sufficient sensitivity and specificity needed to detect levels of infection that lead to transmission
3. no other vertebrate reservoirs and the disease does not amplify in the environment

Question 4

Economic considerations with eradication

Answer 4

Can we justify using limited resources such as money to eliminate a disease. Cost-benefit analyses can be difficult to perform.

**More likely to put resources into alternative health interventions, other non-health societal needs.

Question 5

Social and political criteria for disease eradication

Answer 5

Disease eradication depends on the level of societal and political commitment (from the start to end)

• Likely needs to be of public health importance
• worthy goal for all levels of society
• specific reasons for eradication
• borad national/international appeal

Question 6

Risk or uncertainty

Answer 6

• all disease eradication/control decisions involve uncertainty or risk= “Are we comfortable with the risk”

**important for clinicians and diagnosis (risk and prognosis of a difficult surgery/treatment, evaluate risk and benefits of vaccines, communicate risks of animals contracting disease, warning clients of risks of zoonotic pathogens, disease outbreak risk factors)

Question 7

The precautionary principle

Answer 7

most of us are risk averse

Question 8

Two components of Risk

Answer 8

1. Probability of Harm
2. Severity of impact of a hazard

Question 9

Risk perception and communication

Answer 9

• communication fo risk is a difficult task. Consumers are less aware of probabilities and size of risk, and are more aware of broader qualitative attributes

*balance between observable and controllable

Question 10

Risk communication principles

Answer 10

1. foster partnerships with public (positive relationships with communities)
2. collaborate and coordinate with credible sources (identify subject area experts)
3. meet the needs of media and remain accessible
4. listen to publics concerns and understand your audience
5. communicate with compassion, concern, empathy
6. demonstrate honesty, candor, openness
7. accept uncertainty and ambiguity
8. provide messages that foster self-efficacy (give people meaningful actions)

Question 11

Disease control

Answer 11

• reduction of morbidity and mortality
• a general term which embraces all measures
• an ongoing process
• infers population level control

Question 12

Biosecurity

Answer 12

any practice or system that prevents the spread of infectious agents from infected animals to susceptible animals
(including into uninfected countries, regions, herds)

Question 13

Factors affecting control

Answer 13

• mode of transmission
• host specificity
• ease of spread

Question 14

Important factors in vet disease control

Answer 14

• knowledge of the cause, maintenance and transmission of disease
• vet infrastructure
• diagnostic feasibility
• availability of replacement stock
• producers opinions and cooperation
• public opinion

Question 15

Important factors in disease control programs

Answer 15

• public health considerations
• requirement for legislation and compensation
• ecological consequences
• financial support

Ex. badgers in UK- public would not accept mass culls and they can have ecological impact (change environment without them)

Question 16

Diagnostic tactics

Answer 16

• a diagnosis is not always necessary!
• need to identify elements in the “web of causation” that can be manipulated (such as routes of transmission, indirect causes)
• early detection is important (screening tests are crucial!)

Question 17

Pathognomonic tests

Answer 17

• absolute predictor of disease or disease agent

**Can have false negatives

eg. Culture of Brucella abortus from milk

Question 18

Surrogate tests

Answer 18

detect secondary changes that will hopefully predict the presence or absence of disease or the disease agent
- can have false positives or negatives

Eg. serology, antigen tests, viral isolation etc.

Question 19

Standard of Validity

Answer 19

” Gold Standard”- determine if disease is truly present or absent

• diagnostic test is backed by data comparing its accuracy to an appropriate standard

**sometimes no gold standard for the case exists

Question 20

Post mortem

Answer 20

the ultimate confirmational test

Question 21

Graph diseased vs. non-diseased

Answer 21

Both non-diseased and diseased placed on one graph. Have a cutoff point (animals higher will be positive, animals below will be negative)

Question 22

False negative and positives

Answer 22

• False negatives- the diseased that are below the cutoff point so appear non-diseased (INFECTED)
• False positives- the non-diseased that are above the cut off point so appear positive (NON-INFECTED)

Question 23

Positioning of cut-off points

Answer 23

Diagnostic tests will have cutoff points

• can move the cutoff point, but it will result in decreasing one and increasing the other

Question 24

Diseased vs. non-diseased GRID

Answer 24

Column 1: Disease present (positive, then negative)

Column 2: Disease Absent (positive, then negative)

** provides true positives & negatives, and false positives & negatives**

Question 25

True prevalence

Answer 25

True prevalence= (true positives + false negatives)/Total

Question 26

Apparent Prevalence

Answer 26

Apparent prevalence= (true positives +false positives)/ Total

Question 27

Sensitivity eqn

Answer 27

Sensitivity= true positives/ (true positives+false negatives)

Question 28

Definition: Sensitivity

Answer 28

• proportion of disease animals that test positive

***All about ability of the diagnostic test to detect disease

1-false negative

SnNout

Question 29

What would a highly sensitive test mean?

Answer 29

If highly sensitive test, then a negative test is likely to mean that it is actually negative

Question 29

Specificity eqn

Answer 29

Specificity= true negatives/ (false positives+true negatives)

Question 30

Specificity Definition

Answer 30

Proportion of non-diseased animals that test negative

*** Ability of diagnostic test to detect non-diseased animals

1- false positive rate

SpPin

Question 31

What do you use when you are trying to rule out a disease?

Answer 31

• use a test with high sensitivity and a high negative predictive value
• works best when prevalence of disease is low
• SnNout (sensitivity)

Question 32

What do you use when you are trying to rule in a disease?

Answer 32

• use a test with high specificity and a high positive prevalence value
• works best when the prevalence of disease is high
• SpPin (specificity)

Question 33

What is the cost of a false negative test?

Answer 33

• can have serious consequences
  Ex. exotic disease such as Foot or mouth

**Need to have highly sensitive tests even at the cost of specificity. Avoid false negatives at all costs

Question 34

What is the cost of a false positive test?

Answer 34

• high treatment costs
• treatments that are potentially dangerous
• euthanasia of valuable animal might be possible
• use highly specific tests