1. Control Measures for Infectious Diseases Personal behavior Vaccination Vector control Disinfection –Removal –Inactivation Prevention or Cure

2. Personal behavior Exposure avoidance Handwashing Skin protection Respiratory protection Prophylactic treatment

3. The body’s defenses Skin (passive) Non-specific immune responses –Inflammation (cytokines, macrophages, activated lymphocytes), fever –Phagocytosis by macrophages –Antibody response: IgA, IgM Specific immune responses –Antibody production: IgG specific to target –Memory cells (B-lymphocytes)

4. Cells of the Immune System Bone Marrow Stem Cells Blood lineage Red Blood Cells Platelets Granulocytes Eosinophils, Neutrophils, Basophils Monocytes Macrophages Lymphoid lineage (lymphocytes) NK Cells Pre-B Plasma cells Memory B-cells Pre-T (thymus) T-helper cells T-suppressor cells Memory T cells Cytotoxic T cells Delayed hypersensitivity T cells

5. Vaccination Develop antibodies – attenuate disease Personal or public health measure ? Need to have “critical mass” vaccinated to achieve control of epidemic Practical considerations: cost, side- effects, duration of immunity

6. Some examples Smallpox Flu “Childhood diseases” –Measles, chickenpox Rotavirus Bacterial diseases ? –Tetanus –Anthrax

7. Routes of Transmission Person-to-person: Physical contact Indirect person-to-person –Aerosol –Fomites Vehicle-borne –Food, water Vector-borne –Insects

8. Vector-borne cycle of infection Disease agent is a microorganism Reproduces in a reservoir or host Is transmitted by a vector

9. Vector-borne cycle of infection Example: West Nile Flavivirus Disease agentTarget organisms Reservoirs ? Vector

10. Vector control Vector-borne diseases –E.g. West Nile, malaria Identify vectors, reservoirs –Information on vector life-cycles Eradicate vectors, reservoirs –How ?

12. Mosquitos Pesticides Larvaecides Malathion Naled (an OP) Synthetic pyrethroids Mosquito traps Drain water pools

13. Insecticides Chlorinated hydrocarbons Organophosphates Carbamates

14. Animal Reservoirs Cryptosporidium parvum Single host, eg Beef, calves Oocyst Oocyst excysts, releases 4 sporozoites Sporozoites invade intestinal epithlial cells Sporozoites replicate asexually, differentiate into microgametes and macrogametes Sexual replication More oocysts

15. Is vaccination an option ? Vaccinate vectors ? Reservoirs ? Target species ?

16. Attack disease agent directly Inside host – antibiotics ? In transmission media –Fumigation, sanitization, sterilization

17. Disinfection Physical –Heat, pasteurize, autoclave –Time/temperature dependence Biological –Predation, competition Chemical –Destroy versus prevent reproduction

18. Water disinfectants Chlorine Chlorine dioxide Chloramines Ozone UV light Effectiveness differs with type of organism

19. Chlorine Strong oxidizing agent, relatively stable in water Produced by chloralkali process, electrolysis of salt NaCl in water Chlorine gas, dissolved in water > hypochlorous acid HOCl at low pH, most effective form OCl - (hypochlorite ion) at higher pH –Cl 2 + H 2 O HOCl + H + + Cl - –HOCl H + + OCl - Maintains residual, (provides a disinfectant residual) Formation of THMs Offensive taste/odor

20. Chlorine Dioxide ClO 2 Strong oxidant, though weaker oxidizing agent than chlorine More effective at higher pH Gas, poorly soluble in water Poor residual

21. Chloramines Monochloramine, NH 2 Cl Need chlorine and ammonia gas, generated on-site Weaker oxidizing agent than chlorine Fewer THMs Less offensive taste/odor Poor but stable residual

22. Ozone O 3 Generated on-site Strong oxidizing agent Effective against Giardia Odor/taste not offensive Poorly water-soluble, no residual

23. Ultra-violet light UVA, UVB, UVC –low pressure mercury lamp: low intensity; monochromatic at 254 nm –medium pressure mercury lamp: higher intensity; polychromatic 220-280 nm Less effective in opaque/colored waters No residual Attacks nucleic acids, forms pyrimidine dimers 100290320400 nm UVAUVBUVC

24. Factors Influencing Disinfection Efficacy and Microbial Inactivation Microbe type: Resistance to chemical disinfectants: Vegetative bacteria: Salmonella, coliforms, etc. Enteric viruses: coliphages, HAV, SRSVs, etc. Protozoan (oo)cysts, spores, helminth ova, etc. –Cryptosporidium parvum oocysts –Giardia lamblia cysts –Clostridium perfringens spores –Ascaris lumbricoides ova Acid-fast bacteria: Mycobacterium spp. Least Most

25. Factors Influencing Disinfection Efficacy and Microbial Inactivation Type of Disinfectant and Mode of Action: Free chlorine: strong oxidant; oxidizes various protein sulfhydryl groups; alters membrane permeability; oxidize/denature nucleic acid components, etc. Ozone: strong oxidant Chlorine dioxide: strong oxidant Combined chlorine/chloramines: weak oxidant; denatures sulfhydryl groups of proteins Ultraviolet radiation: nucleic acid damage; thymidine dimer formation, strand breaks, etc.