Disease Control Strategies at the Population Level Flashcards
Disease Eradication
- refers to regional elimination of an infectious disease (Ex. Brucellosis, hog cholera, FMD)
- very few diseases have actually been eradicated (Human Smallpox, Rhinderpest)
Purpose of disease eradication
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
3 things needed for disease eradication
- effective intervention that can interrupt transmission of an agent
- practical diagnostic tools with sufficient sensitivity and specificity needed to detect levels of infection that lead to transmission
- no other vertebrate reservoirs and the disease does not amplify in the environment
Economic considerations with eradication
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.
Social and political criteria for disease eradication
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
Risk or uncertainty
- 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)
The precautionary principle
most of us are risk averse
Two components of Risk
- Probability of Harm
- Severity of impact of a hazard
Risk perception and communication
- 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
Risk communication principles
- foster partnerships with public (positive relationships with communities)
- collaborate and coordinate with credible sources (identify subject area experts)
- meet the needs of media and remain accessible
- listen to publics concerns and understand your audience
- communicate with compassion, concern, empathy
- demonstrate honesty, candor, openness
- accept uncertainty and ambiguity
- provide messages that foster self-efficacy (give people meaningful actions)
Disease control
- reduction of morbidity and mortality
- a general term which embraces all measures
- an ongoing process
- infers population level control
Biosecurity
any practice or system that prevents the spread of infectious agents from infected animals to susceptible animals
(including into uninfected countries, regions, herds)
Factors affecting control
- mode of transmission
- host specificity
- ease of spread
Important factors in vet disease control
- knowledge of the cause, maintenance and transmission of disease
- vet infrastructure
- diagnostic feasibility
- availability of replacement stock
- producers opinions and cooperation
- public opinion
Important factors in disease control programs
- 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)
Diagnostic tactics
- 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!)
Pathognomonic tests
- absolute predictor of disease or disease agent
**Can have false negatives
eg. Culture of Brucella abortus from milk
Surrogate tests
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.
Standard of Validity
” 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
Post mortem
the ultimate confirmational test
Graph diseased vs. non-diseased
Both non-diseased and diseased placed on one graph. Have a cutoff point (animals higher will be positive, animals below will be negative)
False negative and positives
- 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)
Positioning of cut-off points
Diagnostic tests will have cutoff points
- can move the cutoff point, but it will result in decreasing one and increasing the other
Diseased vs. non-diseased GRID
Column 1: Disease present (positive, then negative)
Column 2: Disease Absent (positive, then negative)
** provides true positives & negatives, and false positives & negatives**
True prevalence
True prevalence= (true positives + false negatives)/Total
Apparent Prevalence
Apparent prevalence= (true positives +false positives)/ Total
Sensitivity eqn
Sensitivity= true positives/ (true positives+false negatives)
Definition: Sensitivity
- proportion of disease animals that test positive
***All about ability of the diagnostic test to detect disease
1-false negative
SnNout
What would a highly sensitive test mean?
If highly sensitive test, then a negative test is likely to mean that it is actually negative
Specificity eqn
Specificity= true negatives/ (false positives+true negatives)
Specificity Definition
Proportion of non-diseased animals that test negative
*** Ability of diagnostic test to detect non-diseased animals
1- false positive rate
SpPin
What do you use when you are trying to rule out a disease?
- use a test with high sensitivity and a high negative predictive value
- works best when prevalence of disease is low
- SnNout (sensitivity)
What do you use when you are trying to rule in a disease?
- use a test with high specificity and a high positive prevalence value
- works best when the prevalence of disease is high
- SpPin (specificity)
What is the cost of a false negative test?
- 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
What is the cost of a false positive test?
- high treatment costs
- treatments that are potentially dangerous
- euthanasia of valuable animal might be possible
- use highly specific tests
