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

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

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

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

  18. 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 • Cl2 + H2O <->HOCl + H+ + Cl- • HOCl <-> H+ + OCl- • Maintains residual, (provides a disinfectant residual) • Formation of THMs • Offensive taste/odor

  19. Chlorine Dioxide • ClO2 • Strong oxidant, though weaker oxidizing agent than chlorine • More effective at higher pH • Gas, poorly soluble in water • Poor residual

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

  21. Ozone • O3 • Generated on-site • Strong oxidizing agent • Effective against Giardia • Odor/taste not offensive • Poorly water-soluble, no residual

  22. 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 100 290 320 400 nm UVC UVB UVA

  23. Least Most Factors Influencing DisinfectionEfficacy 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.

  24. Factors Influencing Disinfection Efficacyand 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.

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