Exam 1: Patterns of Disease

Question 1

What is an epidemic?

Answer 1

An increased or unexpected occurrence of cases

Epizootic

Question 2

What is an endemic?

Answer 2

A normal or expected number of cases in time and space

Enzootic

Question 3

What is a pandemic?

Answer 3

Epidemic over a large area

Question 4

What is an epidemic curve?

Answer 4

Visual display of disease occurrence in time

Question 5

What are the 2 basic types of epidemics?

Answer 5

Common source

Propagated

Question 6

What does a common-source epidemic result from?

Answer 6

Exposure to a common source

Question 7

What is it called if the exposure is sudden and brief?

Answer 7

Point (or point-source) epidemic

Question 8

What is it called if the exposure period is prolonged?

Answer 8

Extended common source epidemic

Question 9

What does a propagating epidemic result from?

Answer 9

Animal to animal transmission

Question 10

Is the initial slope of the epidemic curve steeper when the animal density is lower or higher? What in the R0 model influences this?

Answer 10

Higher

Probability of transmission per contact

Question 11

Is the initial slope of the epidemic curve steeper when the infectious period is shorter or longer? What in the R0 model influences this?

Answer 11

Longer

Probability of transmission per contact and duration of infectiousness

Question 12

Is the initial slope of the epidemic curve steeper when animal numbers increase or decrease?

Answer 12

Increase

Question 13

What causes short term trends?

Answer 13

Epidemics

Question 14

What causes cyclical trends?

Answer 14

Periodic changes in susceptible host population
Periodic changes in effective contact
Seasonal trends

Question 15

What causes secular or long term trends?

Answer 15

Long term interaction of host and agent

Question 16

What are potential uses of epidemic curves?

Answer 16

Characterize the source of an epidemic
Assess relative transmission
Determine the mode of transmission
Determine a seasonal pattern
Possibly assess control measures were effective
Prospectively predict what effect interventions will have

Question 17

What is the dissemination rate?

Answer 17

Propensity of infection to spread to other herds

The average number of uninfected herds to which an infectious agent is delivered by each infected herd

Question 18

What does dissemination rate depend on?

Answer 18

Epidemiologic Triad:
Host
Environment (animal movements, behavior of owner, disease control strategies)
Agent

Question 19

If an epidemic were initiated, how would increasing the herd size affect the slope of the epidemic curve?

Answer 19

The slope would become steeper/increase because there are more susceptibles

Question 20

If an epidemic were initiated, how would the herdsman starting to use “mob grazing” affect the slope of the epidemic curve?

Answer 20

Mob grazing is putting a large group of animals on a small area and moving them around
It maximizes production per acre
The epidemic curve would get steeper because you have more incidence for transmission

Question 21

If an epidemic were initiated, how would leaving the herd size the same, but adding replacements from a high health herd affect the slope of the epidemic curve?

Answer 21

The slope would be flatter or steeper
You could argue this either way
Animals from a high health herd are more naïve and you could be exposed to a greater epidemic
Introducing high health animals reduce the chances of starting epidemic
If an epidemic starts in the herd and you have these animals, the epidemic could be greater