Disease Control Flashcards
Three things are necessary to be able to
potentially eradicate an infectious disease
– Effective intervention is available to interrupt
transmission of the agent
– Practical diagnostic tools with sufficient
sensitivity and specificity are available to
detect levels of infection that lead to
transmission
– There are no other vertebrate reservoirs and
the disease does not amplify in the
environment
A disease eradication initiative is largely
dependent on
the level of societal and
political commitment
Two components of RISK
(1) Probability of Harm
(2) Severity of Impact of a
Hazard
8 Factors affecting Risk
Perception
- Catastrophic potential
- Familiarity
- Understanding
- Scientific certainty
- Controllability
- Is exposure voluntary?
- Impact on children
- Dread results
In broad terms what is Disease Control
Reduction of morbidity and mortality
What is Biosecurity
Any practice or system that prevents the spread
of infectious agents from infected animals to susceptible animals.
Any practice that prevents the introduction of
infected animals into a herd, region or country
in which the infection has not occurred.
Factors affecting Control
- Mode of transmission
- Host specificity
- Ease of spread
6 Important Factors in Veterinary
Disease Control Programs
• Knowledge of the cause, maintenance and transmission of the disease • Veterinary infrastructure • Diagnostic feasibility • Availability of replacement stock • Producer’s opinions and cooperation • Public opinion
4 Important Factors in Disease
Control Programs
• Public health considerations • Requirement for legislation and compensation • Ecological consequences • Financial support
Pathognomonic tests
- Absolute predictor of disease or disease agent
* Can have false negatives
Surrogate Tests
- Detect secondary changes that will hopefully predict the presence or absence of disease or the disease agent
- Can have false negatives and false positives
True Prevalence =
True Prevalence = (A+C)/N
Apparent Prevalence =
Apparent Prevalence = (A+B)/N
Sensitivity =
Sensitivity = A/(A+C)
SnNout
If highly sensitive test has a negative result you can rule out false negative
Specificity =
Specificity = D/(B+D)
SpPin
Positive result with specificity test you can rule in.
What does sensitivity test for?
Proportion of diseased animals that test
positive
Ability of diagnostic test to detect disease
What does specificity test for?
Proportion of non-diseased animals that
test negative
Ability of diagnostic test to detect nondiseased
animals
What type of test do you want to run if you are trying to rule out a disease?
Use a test with high sensitivity and a high
negative predictive value.
SnNout
What type of test do you run if you are trying to rule in a disease or
confirm a diagnosis?
Use a test with high specificity and a high
PPV.
SpPin
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
– Multiple tests should be interpreted in series
Strategies for Directed Action
against Disease at the
Population Level
- Selective Slaughter
- Depopulation
- Quarantine
- Reduction of Contact
- Mass treatment
- Mass Immunization
- Education
- Environmental Control
- Applied Ecology
- Genetic Improvement
Selective Slaughter
Test and slaughter
Slowly Spreading disease
More expensive as disease becomes rarer
Example = Brucilosis
Depopulation
Whole pop including non-infected
Rapidly Spreading disease
Example = Foot and Mouth
Quarantine
Physical separation of sick animals from healthy
Difficult with large size areas like wood bison national park
Reduction of Contact
Separate physically
Separate in time - dont milk staph cows b4 clean cows
Example = Staph mastitis
Mass Treatment
Treat all animals (sick and well)
Diseases occurring at very high prevalence
Example: Deworming
Problems: Disease resistance
2 problems with mass immunization?
- Panacea - ppl thin that if vaccinated that they dont have to worry about other preventative measures
- Can interfere with screening (cant tell vaccinated from infected)
Example of Education
Somatic cell count penalty programs
