Control Measures for Infectious Diseases Personal behavior Vaccination Vector control Disinfection...
Transcript of Control Measures for Infectious Diseases Personal behavior Vaccination Vector control Disinfection...
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
• 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)
Cells of the Immune SystemBone Marrow Stem Cells
Blood lineage
Red Blood Cells
Platelets
GranulocytesEosinophils, Neutrophils, Basophils
Monocytes
Macrophages
Lymphoid lineage (lymphocytes)
NK Cells
Pre-B Plasma cells
Memory B-cells
Pre-T(thymus)
T-helper cellsT-suppressor cells
Memory T cells
Cytotoxic T cells
Delayed hypersensitivity T cells
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
Some examples
• Smallpox
• Flu
• “Childhood diseases”– Measles, chickenpox
• Rotavirus
• Bacterial diseases ?– Tetanus– Anthrax
Routes of Transmission
• Person-to-person: Physical contact• Indirect person-to-person
– Aerosol– Fomites
• Vehicle-borne– Food, water
• Vector-borne– Insects
Vector-borne cycle of infection
• Disease agent is a microorganism
• Reproduces in a reservoir or host
• Is transmitted by a vector
Vector-borne cycle of infectionExample: West Nile
Flavivirus
Disease agentTarget organisms Reservoirs
?Vector
Vector control
• Vector-borne diseases– E.g. West Nile, malaria
• Identify vectors, reservoirs– Information on vector life-cycles
• Eradicate vectors, reservoirs– How ?
Mosquitos
• Pesticides
• Larvaecides
• Malathion
• Naled (an OP)
• Synthetic pyrethroids
• Mosquito traps
• Drain water pools
Insecticides
• Chlorinated hydrocarbons• Organophosphates• Carbamates
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
Is vaccination an option ?
• Vaccinate vectors ?
• Reservoirs ?
• Target species ?
Attack disease agent directly
• Inside host – antibiotics ?
• In transmission media– Fumigation, sanitization, sterilization
Disinfection
• Physical– Heat, pasteurize, autoclave– Time/temperature dependence
• Biological– Predation, competition
• Chemical– Destroy versus prevent reproduction
Water disinfectants
• Chlorine
• Chlorine dioxide
• Chloramines
• Ozone
• UV light
• Effectiveness differs with type of organism
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
Chlorine Dioxide
• ClO2
• Strong oxidant, though weaker oxidizing agent than chlorine
• More effective at higher pH
• Gas, poorly soluble in water
• Poor residual
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
Ozone
• O3
• Generated on-site
• Strong oxidizing agent
• Effective against Giardia
• Odor/taste not offensive
• Poorly water-soluble, no residual
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 nmUVAUVBUVC
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.
Least
Most
Factors Influencing Disinfection Efficacy
and Microbial InactivationType 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.