Control Measures for Infectious Diseases
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Transcript of 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
• 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
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
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
• Chlorine gas, dissolved in water > hypochlorous acid HOCl at low pH, most effective form
• Maintains residual
• Formation of THMs
• Offensive taste/odor
Chloramines
• Monochloramine, NH2Cl
• Need chlorine and ammonia gas, generated on-site
• Weaker oxidizing agent
• Fewer THMs
• Less offensive taste/odor
• Poor residual
Ozone
• O3
• Generated on-site
• Strong oxidizing agent
• Effective against Giardia
• Odor/taste not offensive
• Poorly water-soluble, no residual