Causation

Question 1

What are some of the environmental factors that effect the epidemiolgical triad?

Answer 1

Proximity to other holdings
Geographic
Physical
Husbandry
Contact network

Question 2

What are some examples of agent factors?

Answer 2

• Dose
• Toxicity
• Duration of exposure
• Route of exposure

Question 3

What is the sufficient cause model?

Answer 3

Disesaes have multiple sufficient causes
each cause has multiple components
removal of any one component case from a sufficient cause will prevent disease

there is shared components between the sufficient causes

Question 4

When does disease ‘occur’?

Answer 4

It occurs when, within a defined environment, a susceptible host encounters an agent of disease

Question 5

What are some examples of ‘agent factors’ of infectious disease?

Answer 5

• Virulence
• Pathogenicity
• Infectious dose
• Transmission rate
• life cycle
• route of infection

Question 6

According to the sufficient cause model what would removal of one component do?

Answer 6

Prevent disease from occuring

Question 7

What is the Bradford Hills Criteria for causation?

Answer 7

1. Strength of association
2. Consistency
3. Specificity
4. Temporality
5. Biological gradient
6. Plausibility
7. Coherence
8. Experiment
9. Analogy

Question 8

What is a neccesary cause in terms of rothmans model?

Answer 8

a factor or condition that must be present in order for the disease to occur

Question 9

What is a component cause in terms of rothmans model?

Answer 9

A component cause is a cause that factors or contributes to the disease but is not sufficient on its own to cause the disease

Question 10

What is the Bradford-Hill Criteria for plausability?

Answer 10

• The proposed causal mechanism should be biologically plausible
• The causal mechanism must not contradict what is known about the natural history and biology of the disease
• Must be prepared to reinterpret existing understanding of the disease
• cause/effect interpretations of an association should fit with the known facts and observations

Question 11

What are kochs postulates to be considered a cause for a disease?

Answer 11

1. The microorganism must be found in abundance in all organisms
   suffering from the disease, but should not be found in healthy
   organisms.
2. The microorganism must be isolated from a diseased organism and
   grown in pure culture
3. The cultured microorganism should cause disease when introduced
   into a healthy organism.
4. The microorganism must be reisolated from the inoculated, diseased
   experimental host and identified as being identical to the original
   specific causative agent.

Question 12

What are some agent factors that effect infectious diseases?

Answer 12

• Virulence (severity of the disease)
• Pathogenicity (the ability of the agent to cause disease in a particular host)
• Transmission rate (the average number of new cases attributable to one case during the infectious period
• Life cycle, e.g vectors etc.
• Route of infection

Question 13

What happens if you remove any of the component causes from the sufficient cause?

Answer 13

It prevents disease