Epidemic Models and Herd Immunity Flashcards
10 acheivments of public health?
control infectious dz
vaccination
motor vehicle safety
safer workplace
decline death rate of coronary heart dz , strokes
safe/ healthy food
healthier mothers and babies
family planninf
flouridation of dirnking water
tobacco is health risk
T/F: Immunizations have lead to the global eradication of smallpox and rinderpest
TRUE
Top leading causes of death in 1900 and 1997?
1900 - Pneumonia or TB
1997 - Heart dz or cancer
concept in nature of a population level phenomenon which accounts for the reduction in transmission of infectious diseases
**Herd Immunity **
What are causes of alterations in susceptibilty and conditions?
New or susceptible animals introduced
change in management pratices
diference in vaccination rates
**T/F: **the level of herd immunity needed to control a disease varies?
TRUE
depends on agent/ managment
highly infectious agents require ~ 95 % immunity
The case study involving the lack of MMR vaccine in the UK that lead to measles outbreaks is an example of
Herd Immunity
Measuring herd immunity?
study prevalence of antibodies in a population
“Sero- epidemiology”
Why would the % of immune individuals in a herd be different form the % of vaccinated individuals?
Vaccine failure rate
natural infection-immunity
What are two common models of disease management programs?
R0 and Reed - Frost
What is the purpose of designing disease management programs?
establish a minimum level of herd immunity or other intervention
**Goal **is to prevent sustained transmission
epidemic models predict thresholds
What is the basic reproductive number R0and what does it determine?
number of secondary cases caused by an infected individual in an entirely susceptible population
determines whether dz can persist and valuable for assessing managment options
what happens to a dz If the R0< 1
it will go extinct
What suggests the **average number of new cases **that should be caused by each existing cases
R0
**R0= reproductive rate **
# contacts per day
X
prob. trans / contact
X
days infective
How can you Manage # of contacts per day to decrease **R0? **
isolation
quarantine
hygeine/ clean
Isolation vs Quarantine
Isolate sick animals from potential contacts
- parvo
- horse with salmonella
Quarantine stops all movements of ALL animals, sick or healthy, in and out of area
- stop intake / road blocks
**T/F: **80% of herd immunity will always be sufficient enough to manage measles
False
it is highly contagious and may need more than 80%
What populations do Reed - Frost compartment models consist of?
**S - I - R **
Susceptible
Infectious cases
Resistant (recovered) / Immune or dead
The reed frost model is based upon…?
probability of transmission froma population of infected cases to population of susceptible animals
T/F: The reed frost model depends on the same variables of R0
**False **
**reed frost depends on **
probability of effective contact (P)
of infectious hosts ( C = cases)
of susceptible hosts (S)
What is an iterative (mathematical repetitive) model that accounts for the effects of immunity?
Reed forst model
immune animals are removed from the susceptible population with each iteration
What will reduce S (susceptible) in reed frost model?
vaccination
isolation / quarantine
what till reduce P (effective contacts)
direct transmission
(treat, disinfect, carcass disposal)
Indirect transmission
reduce vectors, treat h20, fence off streams
disinfect premises
handle sick animals after healthy ones
Summarize steps in the develpoment and use of model
ID the question
ID relevant facs about infection in question
choose model method
specify model input
set up model
model validation
predict/ optimization
**T/F: **In a herd immunity model, when a virus is introduced into a population with initial herd immunity approaching the threshold of invasion, **Low amplitude, persistent smoldering epidemcs may occur? **
True
**T/F: **when virus is introduced into a more susceptible population, High Amplitude, shorter epidemics may results
True
