Transcript Control Measures for Infectious Diseases

Control Measures for Infectious
Diseases
Prevention or Cure
•
•
•
•
Personal behavior
Vaccination
Vector control
Disinfection
– Removal
– Inactivation
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 System
Bone Marrow Stem Cells
Blood lineage
Red Blood Cells
Lymphoid lineage (lymphocytes)
NK Cells
Platelets
Pre-B
Granulocytes
Eosinophils,
Neutrophils,
Basophils
Monocytes
Macrophages
Plasma cells
Memory B-cells
Pre-T
(thymus)
T-helper cells
T-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, sideeffects, 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 infection
Example: West Nile
Target
organisms
Disease agent
Flavivirus
Vector
Reservoirs
?
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
• UVA, UVB, UVC
Ultra-violet light
– 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
Factors Influencing Disinfection
Efficacy and Microbial Inactivation
• Microbe type: Resistance to chemical disinfectants:
• Vegetative bacteria: Salmonella, coliforms, etc.
• Enteric viruses: coliphages, HAV, SRSVs, etc.
Least
• Protozoan (oo)cysts, spores, helminth ova, etc.
– Cryptosporidium parvum oocysts
– Giardia lamblia cysts
– Clostridium perfringens spores
– Ascaris lumbricoides ova
• Acid-fast bacteria: Mycobacterium spp.
Most
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.