1. This presentation is made available through a Creative Commons Attribution- Noncommercial license. Details of the license and permitted uses are available at http://creativecommons.org/licenses/by-nc/3.0/ © 2010 Dr. Juliet Pulliam http://creativecommons.org/licenses/by-nc/3.0/ Title: Dynamics of Directly-Transmitted Pathogens Attribution: Dr. Juliet Pulliam, Topics in Biomedical Sciences Source URL: http://lalashan.mcmaster.ca/theobio/mmed/index.php/Honours Coursehttp://lalashan.mcmaster.ca/theobio/mmed/index.php/Honours Course For further information please contact Dr. Juliet Pulliam (juliet.mmed.clinic@gmail.com).

2. Dynamics of directly-transmitted pathogens Topics in Biomedical Sciences BSc Honours Course in Biomathematics African Institute for the Mathematical Sciences Muizenberg, South Africa 18 May 2009 Dr. Juliet Pulliam RAPIDD Program Division of International Epidemiology Fogarty International Center National Institutes of Health (USA)

3. Transmission Infectious diseases Mode of transmission Direct transmission Direct contact Droplet spread Indirect transmission Airborne Vehicle-borne (fomites) Vector-borne (mechanical or biological) Portal of entry Portal of exit

4. Transmission Infectious diseases Mode of transmission Direct transmission Direct contact Droplet spread Indirect transmission Airborne Vehicle-borne (fomites) Vector-borne (mechanical or biological) Portal of entry Portal of exit Sexual contact (STD’s) Casual contact (OID’s)

5. Directly-transmitted pathogens “Typical” natural history Onset of symptoms Onset of shedding IncubationClinical disease Infectious periodLatent period Infection

6. Directly-transmitted pathogens “Typical” natural history Onset of symptoms Onset of shedding IncubationClinical disease Infectious periodLatent period Infection Acute: timecourse of infection << normal lifespan of host Immunizing: infection stimulates antibody production, preventing future infection

7. Directly-transmitted pathogens Examples Whooping cough Chicken pox Measles Smallpox Various food-borne illnesses

8. A simple view of the world Directly-transmitted pathogens Infected=Infectious Infection Onset of shedding Infectivity = 1 Don’t worry about symptoms and disease! ^ very!

9. A simple view of the world Directly-transmitted pathogens Infected Diseased Infectivity = 1 Onset of symptoms Onset of shedding IncubationClinical disease Infectious periodLatent period Infection Infectious =

10. A realistic view of the world Directly-transmitted pathogens Infected Diseased Infectivity < 1 Onset of symptoms Onset of shedding IncubationClinical disease Infectious periodLatent period Infection Infectious = ^ more

11. A realistic view of the world Directly-transmitted pathogens Infected Diseased Infectivity < 1 Onset of symptoms Onset of shedding IncubationClinical disease Infectious periodLatent period Infection Infectious = ^ more  = infectivity x per capita contact rate

12. A realistic view of the world Directly-transmitted pathogens Diseased Infectious = ^ more (not infectious) Infected

13. A realistic view of the world Directly-transmitted pathogens Diseased Infectious = ^ more Susceptible Recovered (not infectious) Infected

14. A realistic view of the world Directly-transmitted pathogens Diseased Infectious = ^ more Susceptible Recovered (not infectious) Infected

15. A realistic view of the world Directly-transmitted pathogens Diseased Infectious = ^ nearly Susceptible Recovered (not infectious) Infected

16. A realistic view of the world Directly-transmitted pathogens Diseased Infectious = ^ nearly Susceptible Recovered (not infectious) Infected

17. A realistic view of the world Directly-transmitted pathogens ^ nearly S EI R exposed & infected

18. A realistic view of the world Directly-transmitted pathogens ^ nearly R birth rate mortality rate 1/latent period 1/infectious period transmission coefficient

19. A realistic view of the world Directly-transmitted pathogens ^ nearly R Assume constant population size

20. A realistic view of the world Directly-transmitted pathogens ^ nearly

21. A realistic view of the world Directly-transmitted pathogens ^ nearly Rate at which an infected individual produces new infections in a naïve population X Proportion of new infections that become infectious X Average duration of infectiousness

22. A realistic view of the world Directly-transmitted pathogens ^ nearly

23. A realistic view of the world Directly-transmitted pathogens ^ nearly Equilibria… Disease free equilibrium Endemic equilibrium

24. A realistic view of measles Directly-transmitted pathogens ^ nearly individuals/year years -1 days -1 (unknown)

25. A realistic view of measles Directly-transmitted pathogens ^ nearly From: Grenfell & Harwood 1997 Trends in Ecology and Evolution

26. A realistic view of measles Directly-transmitted pathogens ^ nearly ~ 7,200 From: Grenfell & Harwood 1997 Trends in Ecology and Evolution ~ 300,000 ~ 500,000

27. A realistic view of measles Directly-transmitted pathogens ^ nearly From: Anderson & May 1982 Science

28. A realistic view of measles Directly-transmitted pathogens ^ nearly N = 7,200N = 300,000N = 500,000

29. A realistic view of measles Directly-transmitted pathogens ^ nearly Critical community size From: Grenfell & Harwood 1997 Trends in Ecology and Evolution

30. A realistic view of measles Directly-transmitted pathogens individuals/year years -1 days -1 seasonal (school terms)

31. A realistic view of measles Directly-transmitted pathogens From: Earn et al. 2000 Science

32. A realistic view of measles Directly-transmitted pathogens From: Earn et al. 2000 Science

33. A realistic view of measles Directly-transmitted pathogens From: Earn et al. 2000 Science