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Disease Transmission

Disease Transmission. Terms Associated with Disease Causation & Transmission. Host Agent Environment Fomites Vector Carrier – active Incubatory Convalescent Healthy Intermittent. You will cover these in today’s discussion. Modes of Transmission. Direct Indirect.

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Disease Transmission

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  1. Disease Transmission

  2. Terms Associated with Disease Causation & Transmission • Host • Agent • Environment • Fomites • Vector • Carrier – active • Incubatory • Convalescent • Healthy • Intermittent You will cover these in today’s discussion.

  3. Modes of Transmission • Direct • Indirect

  4. Chain of Infection • Etiological agent • Source/Reservoir • Portal of exit • Mode of transmission • Portal of entry • Susceptible host

  5. Forms of Disease • Clinical • acute • sub-acute • Non-clinical (Inapparent) • pre-clinical • sub-clinical • chronic (persistent) • latent Your Assignment: familiarize yourself with the definitions of these terms

  6. Disease Investigation • Establish diagnosis • Identify specific agent • Describe according to person, place and time • Identify source of agent • Identify mode of transmission • Identify susceptible populations

  7. Steps in the Investigation of an Epidemic • Define the epidemic • Examination the distribution of cases • Look for combinations of variables • Develop hypothesis (es) • Test hypothesis • Recommend control measures

  8. Determinants of Disease Outbreak • Based on balance of disease in a population • herd immunity • disease restricted to single host • transmission must be relatively direct

  9. Effect of Herd Immunity

  10. Incubation Period • The period of time after an infection is established but before the first signs or symptoms appear • Different diseases generally have different incubation times and symptoms • Therefore, can derive epidemic curves

  11. Epidemic Curve for Single Exposure Common-Vehicle Outbreak

  12. Incubation Period ???????Dependent upon: D = (N)(V) / I Your Assignment: define the variables in this formula

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