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Disease transmission and control
Defining Control objectives and strategies
WHO/CSRWHO/CSR
Epidemiological Surveillance and Epidemic Response UnitEpidemiological Surveillance and Epidemic Response Unit
Division of Emerging and Other Communicable DiseasesDivision of Emerging and Other Communicable Diseases
Before we can talk about control measures we must assess our knowledge on:
• Disease transmissionDisease transmission– reservoir, sources, routesreservoir, sources, routes
• Infectious process Infectious process – exposure, infection, disease exposure, infection, disease
• Pathogenesis of disease statePathogenesis of disease state– target organs, virulence, immuneresponsetarget organs, virulence, immuneresponse
• Natural historyNatural history• Effectiveness of control measuresEffectiveness of control measures
WHO/CSRWHO/CSR
Major transmission routes
Direct
Vector borne
Environmental
Droplet
Sexual
Blood
Skin to skin
Other
Insects
Animals
Food
Water
WHO/CSRWHO/CSR
AirborneDrop. nuclei
Dust
Does a potential control measure reduce
• TransmissionTransmission• ExposureExposure• InfectionInfection• DiseaseDisease• DeathDeath• DisabilityDisability
WHO/CSRWHO/CSR
?
Principles of control
• Prevent exposure• Protect susceptibles from infection• Prevent progression from infection to disease• Treat cases
– Prevent death and disability– Prevent further transmission
• Interrupt transmission– Environmental – Social/behavioural– Legal
WHO/CSRWHO/CSR
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
WHO/CSRWHO/CSR
Pathways of Disease Transmission
IncubationPeriod
PATHOGEN
PATHOGENHOST
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
WHO/CSRWHO/CSR
Susceptibility- previous exposure- immunity- compromise- prophylaxis
HOST
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
WHO/CSRWHO/CSR
General healthNutritionImmunityVirulenceImmune responseProphylaxis
HOST
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
WHO/CSRWHO/CSRTreatment
HOST
Control
– Where does it fit in?
WHO/CSRWHO/CSR
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
7
2
5
4
6
Points for controlmeasures
3WHO/CSRWHO/CSR
Disability
1
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
1
Points for controlmeasures
WHO/CSRWHO/CSRDisability
Vaccination
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
2
Points for controlmeasures
WHO/CSRWHO/CSRDisability
Prophylaxis
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
Points for controlmeasures
3WHO/CSRWHO/CSR
Disability
TreatmentRehabilitation
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
5
4
Points for controlmeasures
WHO/CSRWHO/CSRDisability
IsolationTreatment
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
6
Points for controlmeasures
WHO/CSRWHO/CSRDisability
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
7
Points for controlmeasures
WHO/CSRWHO/CSRDisability
Isolation
RepellentsBed nets
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
1
2
5
4
6
Points for controlmeasures
3 WHO/CSRWHO/CSRDisability
Vaccination
Prophylaxis
Isolationtreatment
Treatment
RepellentsBednets7
Approach to control
• What is feasible?
• What is available?
• What is effective?
• What is affordable?
WHO/CSRWHO/CSR
What is the overall control objective ?
• Endemic disease control by• reducing incidence• reducing mortality
• Epidemic prevention and control• Elimination• Eradication
WHO/CSRWHO/CSR
Control objectives should be
• Realistic
• Quantitative (time, place, person)
• Periodically evaluated
• Flexible
WHO/CSRWHO/CSR
Exposure
Infection
Disease
Death Recovery
Direct
Vector
Envir
WHO/CSRWHO/CSR
SPECIFIC EXAMPLESOF CONTROL
Exposure
Infection
Disease
Droplet
M. tb
TUBERCULOSIS
Death RecoveryDisability
Exposure
Infection
Disease
Droplet
Vaccination?? - BCG
Prophylaxis??
Treatment
M. tb
TUBERCULOSIS
Death RecoveryDisability
Isolation??
Exposure
Infection
Disease
Direct
Diphtheria
Death RecoveryDisability
Exposure
Infection
Disease
Direct
Vaccination - DPT
Prophylaxis
Diphtheria
Treatment
Death RecoveryDisability
Isolation
Treatment
Exposure
Infection
Disease
Death Recovery
Vector
Dengue
Aedes Aedes aegyptiaegypti
WHO/CSRWHO/CSR
Exposure
Infection
Disease
Death Recovery
Vector
Dengue
Aedes Aedes aegyptiaegypti
Protection
Breeding sitesInsecticide
WHO/CSRWHO/CSRCase management
Exposure
HIV +
AIDS
Death
Direct
HIV/AIDS
Sexual
Blood IVDUIatrogenic
Exposure
HIV +
AIDS
Death
Direct
Vaccine ???
ART
HIV/AIDS
Sexual
Blood IVDUIatrogenic
Behaviour
ART
Exposure
Infection
Disease
Death Recovery
Direct
Measles
Highly infectiousR0 = 10-20
WHO/CSRWHO/CSR
Exposure
Infection
Disease
Death Recovery
Direct
Vaccination
Measles
Highly infectiousR0 = 10-20
WHO/CSRWHO/CSRCase management
Vitamin A
Exposure
Infection
Disease
Death Recovery
Direct
Poliomyelitis
WHO/CSRWHO/CSR
Envir
?
Exposure
Infection
Disease
Death Recovery
Direct
Vaccination
Poliomyelitis
WHO/CSRWHO/CSR
Envir
Case managementRehabilitation
?
Global Eradication of Poliomyelitis
Definition:
Complete interruption of wild poliovirus
transmission
Uses of surveillance
• How would surveillance help in achieving How would surveillance help in achieving control objectives?control objectives?
• How would it help in dealing with epidemic How would it help in dealing with epidemic disease?disease?
WHO/CSRWHO/CSR
Thank you