midterm II schematics of principles of disease spread Flashcards
what is sensitivity?
it is A/(A+C)
it is how well a test detects positive diseased animals
it is the proportion of diseased animals that test positive
it measure the abillity of a diagnostic test to detect disease
= (1-false negative rate)
A/(A+C)
SnNout
what is SnNout?
if you have a highly sensitive test, then a negative test means you can rule disease out
what is specificity?
it si the proportion of non-diseased animals that test negative
it measures the ability of a diagnostit test to detect non-diseased animals
it is 1-false positive rate
D/(B+D)
it is SpPin
what is SpPin?
if a test is highly specific, and there is a positive result, then you can rule disease in
what kind of test do you use if you are trying to rule out disease?
a test with high sensitivity and a high negative predictive value; it works best when the pre-test probability of the disease is low
what kind of test should you use if you are trying to rule in disease?
a test with high specificity and a high PPV
it works best when the pre-test probability of disease is high
when should a highly sensitive test be used?
it depends on the situation; exotic diseases bad consequences are disasterous; need highly specific test to rule out disease; avoid false negatives at all costs
multiple tests should be interpreted in parallel
when should a highly specific test be used?
when the cost of the false positive test are high
high treatment costs
euthanasia of valuable animal
multiple tests should be considered in series
what are 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
what is selective slaughter?
testing animals and slaughtering them; deliberate killing of a minority to protect the majority; works well early in dsease outbreaks and in slowly spreading disease but is a difficult approach to sell because it becomes more difficult as the disease becomes rarer
what is depopulation?
it is a method of controlling disease where the whole population including non-infected individuals is sacrificed
a diagnostic test is not easily applied or is inaccurate
the population is inaccessible
it is a rapidly spreading disease
it is an exotic disease
it is the terminal stages of eradication programs
what resources were utilized for the foot and mouth disease problem in the UK?
1000 vets
2000 army troops
1000 police officers
15 000 vehicles
tonnage of carcasses greater than ammunition moved by brit troops in gulf war
200 olympic sized swimming pools excavated
1 mass burial site had 430 000 head
what is quarantine?
it is a method of disease control where sick animals or potentially sick animals are physically separated; this involves restraining movement of exposed or infected animals or items that may be contaminated “biosecurity”
national, regional, herd or within farm level
Specific pathogen free barns, importantion quarantines etc
what is reduction of contact method?
reduce or prevent contact (physical or aerosol) between infected and non-infected animals
separate them in time (all in all out chicken barn, milk staph cows last)
physical separation (calf hutches, creep areas for beef calves)
which herds are more at risk for infectious diseases?
dealer herds or expanding herds
