Epidemic Models and Herd Immunity

Question 1

10 acheivments of public health?

Answer 1

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

Question 2

T/F: Immunizations have lead to the global eradication of smallpox and rinderpest

Answer 2

TRUE

Question 3

Top leading causes of death in 1900 and 1997?

Answer 3

1900 - Pneumonia or TB

1997 - Heart dz or cancer

Question 4

concept in nature of a population level phenomenon which accounts for the reduction in transmission of infectious diseases

Answer 4

**Herd Immunity **

Question 5

What are causes of alterations in susceptibilty and conditions?

Answer 5

New or susceptible animals introduced

change in management pratices

diference in vaccination rates

Question 6

**T/F: **the level of herd immunity needed to control a disease varies?

Answer 6

TRUE

depends on agent/ managment

highly infectious agents require ~ 95 % immunity

Question 7

The case study involving the lack of MMR vaccine in the UK that lead to measles outbreaks is an example of

Answer 7

Herd Immunity

Question 8

Measuring herd immunity?

Answer 8

study prevalence of antibodies in a population

“Sero- epidemiology”

Question 9

Why would the % of immune individuals in a herd be different form the % of vaccinated individuals?

Answer 9

Vaccine failure rate

natural infection-immunity

Question 10

What are two common models of disease management programs?

Answer 10

R₀ and Reed - Frost

Question 11

What is the purpose of designing disease management programs?

Answer 11

establish a minimum level of herd immunity or other intervention

**Goal **is to prevent sustained transmission

epidemic models predict thresholds

Question 12

What is the basic reproductive number R₀and what does it determine?

Answer 12

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

Question 13

what happens to a dz If the R₀< 1

Answer 13

it will go extinct

Question 14

What suggests the **average number of new cases **that should be caused by each existing cases

Answer 14

R₀

**R₀= reproductive rate **

# contacts per day

X

prob. trans / contact

X

days infective

Question 15

How can you Manage # of contacts per day to decrease **R₀? **

Answer 15

isolation

quarantine

hygeine/ clean

Question 16

Isolation vs Quarantine

Answer 16

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

Question 17

**T/F: **80% of herd immunity will always be sufficient enough to manage measles

Answer 17

False

it is highly contagious and may need more than 80%

Question 18

What populations do Reed - Frost compartment models consist of?

Answer 18

**S - I - R **

Susceptible

Infectious cases

Resistant (recovered) / Immune or dead

Question 19

The reed frost model is based upon…?

Answer 19

probability of transmission froma population of infected cases to population of susceptible animals

Question 20

T/F: The reed frost model depends on the same variables of R₀

Answer 20

**False **

**reed frost depends on **

probability of effective contact (P)

of infectious hosts ( C = cases)

of susceptible hosts (S)

Question 21

What is an iterative (mathematical repetitive) model that accounts for the effects of immunity?

Answer 21

Reed forst model

immune animals are removed from the susceptible population with each iteration

Question 22

What will reduce S (susceptible) in reed frost model?

Answer 22

vaccination

isolation / quarantine

Question 23

what till reduce P (effective contacts)

Answer 23

direct transmission

(treat, disinfect, carcass disposal)

Indirect transmission

reduce vectors, treat h20, fence off streams

disinfect premises

handle sick animals after healthy ones

Question 24

Summarize steps in the develpoment and use of model

Answer 24

ID the question

ID relevant facs about infection in question

choose model method

specify model input

set up model

model validation

predict/ optimization

Question 25

**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? **

Answer 25

True

Question 26

**T/F: **when virus is introduced into a more susceptible population, High Amplitude, shorter epidemics may results

Answer 26

True