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