Understanding Infectious Diseases: An Epidemiological Overview

5. EPIDEMIOLOGY

6. Koch’s Postulates (1876)

7. Koch’s Postulates • To prove that a given microorganism is the pathogen for a certain disease one must • Isolate From Afflicted Individual • Culture • Reinfect Previously Unafflicted Individual • The previously unafflicted individual must develop the same symptoms/disease state as the original host

9. Host • Def: Individual afflicted with disease • Factors Affecting Host • Genetic Predisposition • Active Immunity • Other diseases

10. Example: Individuals with Thalassemia Are Not Good Hosts For Malaria

11. Reservoir • Def: Naturally occurring population that carries the pathogen. Continual source of pathogen. • Example: Cows and Anthrax

12. Antigenic Shift • Def: Mutation in the pathogen population that changes their antigens (i.e. proteins that identify them to our immune systems) • Antigenic shifts allow diseases to jump from one species to another

16. Pathogen • Def: What causes the disease in the host

17. One pathogen: One disease • The causative agent of Anthrax is Bacillus anthracis. • The causative agent of Lyme Disease is Borelliaburgdorferi • You cannot get Lyme Disease from Bacillus anthracis

18. Vector • Def: The agent that transfers the pathogen from host to host

20. Mosquitoes • Most dangerous animal in world (for humans) • Vectors for malaria, dengue, encephalitis, yellow fever, heartworm

21. EPI Curves

23. What causes some diseases to become pandemic while others are epidemic or endemic?

24. R0 = Basic Reproductive Number • Measurement of how many cases will generally derive from a single case of a given disease • R0 < 1 = disease will not spread • R0 > 1 = disease will spread

25. Comparative R0 Values

26. Virulence • Def: How much does the pathogen affect the host • Example: Ebola is so virulent, killing the host so rapidly, that it is difficult for the disease to spread to other hosts

27. Endemic • A disease that is commonly present in a population, generally at low frequencies • Ex: Malaria, Streptococcus A

28. Epidemic • Large number of afflicted hosts in a small area in a short period of time • Epidemics are generally short-lived due to rapid virulence/effects and limited number of hosts • EX: Ebola

29. PANDEMIC • Disease that spreads worldwide, creating thousands of cases • Generally, pandemic diseases require common vectors and long incubations or lysogenic modes • Ex: Tuberculosis

30. Sudden Acute Respiratory Syndrome

32. How Does The Balance of The Viral Life Cycles Determine If A Disease Is An Epidemic, Endemic or Pandemic?

34. LAB: Interactive Epidemiology • Purpose: To examine the effects of several parameters of communicable diseases on their epidemiological profile • Method: mathematical modeling

35. Part 1: NIH Disease Transmission Simulator

37. Part Two: Pop. Density & Mobility