Vet 435 Epidemiology Review

Front 1

Define:
Epidemiology

Back 1

-the study of factors determining the occurence of disease in a population

Front 2

What is a cause of disease?
Define:
1. sufficient cause
2. necessary cause
3. component cause

Back 2

-factor, event or characteristic that plays an essential role in the occurence of a disease
1. factor can cause disease
2. factor must be present
3. one of several factors leading to a sufficient cause

Front 3

Why determine the cause of disease

Back 3

so that we can implement a control or treatment programme

Front 4

Define:
-confounding variable

Back 4

-a link to some other factor
-'red herrrings'
-leads to misleading associations
-often host characteristics, management or hereditary factor

Front 5

Establishing a causal relationship (factors)

Back 5

-Time: cause must precede disease
-Strong association: odds ratios/relative risk (measure of how important a factor is)
-dose response: favours causation
-Consistency across studies (meta-analysis)
-Compatibility w/ existing knowledge
-biological plausibility
(NB last three not always predictable)

Front 6

Causes of disease

Back 6

-infectious agent
-toxin
-nutritional factor (deficiency/excess)
-physiological factor
-behavioural/management factor
-social factor

Front 7

List 3 important epidemiological concepts

Back 7

1. disease never occurs randomly
2. diseases are multifactorial
3. disease is an interaction between host, agent and environment

Front 8

List 10 host factors contributing to disease

Back 8

-age
-gender
-species
-breed
-strain
-physiological status
-husbandry
-management
-stress
-social factors

Front 9

List 4 agent factors contributing to disease

Back 9

-infectivity
-pathogenicity
-virulence
-non-infectious agents

Front 10

define: incidence

Back 10

-new cases of disease in the population at-risk over a specific period of time
-measures risk or likelihood of an individual animal contracting disease
-three measures of incidence

Front 11

Define: Incidence count

Back 11

-count of new cases observed in a population over a short period of time

Front 12

Define: cumulative incidence/incidence risk

Back 12

-proportion of non-diseased animals at the start of a period that become diseased during the period
-only the first occurrence of disease is considered
-measures risk of developing disease

Front 13

Define: incidence rate/indicence density

Back 13

-new cases of disease in a period divided by the total animal time at risk
-measures speed of disease spread

Front 14

List Evan's postulates (10)

Back 14

1. prevalence is higher in exposed group
2. exposure to cause more frequent in diseased group
3. incidence higher in group exposed to cause
4. disease occurs after exposure
5. range of host responses should occur
6. measurable host responses should occur
7. disese more frequently in experimentally challenged group
8. Eliminating/modifying cause should decrease disease incidence
9. preventing/modifying host response should decrease frequency/severity of disease
10. relationships should be biologically and epidemiologically credible

Front 15

define: incidence risk

Back 15

-calculated by dividing the number of new cases developing in a period by the number who were disease free at the start of the period

Front 16

define: incidence rate

Back 16

-calculated by dividing the number of new cases developing in a period by the average number who were disease free over the period

Front 17

Relation between prevalence and incidence rate

Back 17

P=IR X D (duration)

Front 18

Factors altering incidence and prevalence

Back 18

-changes in diagnostic technique
-disease classification, clarification and nomenclature change
-regulations and their changes in time
-professional or government interest
-presence of other diseases
-population changes
-environmental changes