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Control Measures for Infectious Diseases

Control Measures for Infectious Diseases. Personal behavior Vaccination Vector control Disinfection Removal Inactivation. Prevention or Cure. Personal behavior. Exposure avoidance Handwashing Skin protection Respiratory protection Prophylactic treatment. The body’s defenses.

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Control Measures for Infectious Diseases

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  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 Lymphoid lineage (lymphocytes) NK Cells Red Blood Cells Plasma cells Pre-B Platelets Memory B-cells Granulocytes Eosinophils, Neutrophils, Basophils Pre-T (thymus) T-helper cells T-suppressor cells Memory T cells Monocytes Cytotoxic T cells Delayed hypersensitivity T cells Macrophages

  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 Target organisms Disease agent Reservoirs Flavivirus Example: West Nile Vector ?

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

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

  12. Insecticides • Chlorinated hydrocarbons • Organophosphates • Carbamates

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

  14. Cryprosporidium life-cycle

  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 • Chlorine gas, dissolved in water > hypochlorous acid HOCl at low pH, most effective form • Maintains residual • Formation of THMs • Offensive taste/odor

  20. Chlorine Dioxide • Weaker oxidizing agent • More effective at higher pH • Poor residual

  21. Chloramines • Monochloramine, NH2Cl • Need chlorine and ammonia gas, generated on-site • Weaker oxidizing agent • Fewer THMs • Less offensive taste/odor • Poor residual

  22. Ozone • O3 • 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 • Attacks nucleic acids • Less effective in opaque/colored waters • No residual

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