Disease transmission and control Defining Control objectives and strategies WHO/CSR Epidemiological Surveillance and Epidemic Response Unit Division of Emerging and Other Communicable Diseases

Before we can talk about control measures we must assess our knowledge on: Disease transmissionDisease transmission –reservoir, sources, routes Infectious processInfectious process –exposure, infection, disease Pathogenesis of disease statePathogenesis of disease state –target organs, virulence, immuneresponse Natural historyNatural history Effectiveness of control measuresEffectiveness of control measures WHO/CSR

Major transmission routes Direct Vector borne Environmental Droplet Sexual Blood Skin to skin Other Insects Animals Food Water WHO/CSR Airborne Drop. nuclei Dust

Does a potential control measure reduce TransmissionTransmission ExposureExposure InfectionInfection DiseaseDisease DeathDeath DisabilityDisability WHO/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/CSR

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir WHO/CSR Pathways of Disease Transmission Incubation Period PATHOGEN HOST

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir WHO/CSR Susceptibility - previous exposure - immunity - compromise - prophylaxis HOST

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir WHO/CSR General health Nutrition Immunity Virulence Immune response Prophylaxis HOST

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir WHO/CSR Treatment HOST

Control –Where does it fit in? WHO/CSR

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir Points for control measures 3 WHO/CSR Disability 1

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir 1 Points for control measuresWHO/CSR Disability Vaccination

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir 2 Points for control measuresWHO/CSR Disability Prophylaxis

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir Points for control measures 3 WHO/CSR Disability Treatment Rehabilitation

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir 5 4 Points for control measuresWHO/CSR Disability Isolation Treatment

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir 6 Points for control measuresWHO/CSR Disability

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir 7 Points for control measuresWHO/CSR Disability Isolation Repellents Bed nets

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir Points for control measures 3 WHO/CSR Disability Vaccination Prophylaxis Isolation treatment Treatment Repellents Bednets 7

Approach to control What is feasible? What is available? What is effective? What is affordable? WHO/CSR

What is the overall control objective ? Endemic disease control by reducing incidence reducing mortality Epidemic prevention and control Elimination Eradication WHO/CSR

Control objectives should be Realistic Quantitative (time, place, person) Periodically evaluated Flexible WHO/CSR

Exposure Infection Disease DeathRecovery DirectDirect VectorVector EnvirEnvir WHO/CSR SPECIFIC EXAMPLES OF CONTROL

Exposure Infection Disease DropletDroplet M. tb TUBERCULOSIS DeathRecovery Disability

Exposure Infection Disease DropletDroplet Vaccination ?? - BCG Prophylaxis ?? Treatment M. tb TUBERCULOSIS DeathRecovery Disability Isolation ??

Exposure Infection Disease DirectDirect Diphtheria DeathRecovery Disability

Exposure Infection Disease DirectDirect Vaccination - DPT Prophylaxis Diphtheria Treatment DeathRecovery Disability Isolation Treatment

Exposure Infection Disease DeathRecovery VectorVector Dengue Aedesaegypti WHO/CSR

Exposure Infection Disease DeathRecovery VectorVector Dengue Aedesaegypti Protection Breeding sites Insecticide WHO/CSR Case management

Exposure HIV + AIDS Death DirectDirect HIV/AIDS Sexual Blood IVDU Iatrogenic

Exposure HIV + AIDS Death DirectDirect Vaccine ??? ART HIV/AIDS Sexual Blood IVDU Iatrogenic Behaviour ART

Exposure Infection Disease DeathRecovery DirectDirect Measles Highly infectious R 0 = WHO/CSR

Exposure Infection Disease DeathRecovery DirectDirect Vaccination Measles Highly infectious R 0 = WHO/CSR Case management Vitamin A

Exposure Infection Disease DeathRecovery DirectDirect Poliomyelitis WHO/CSR EnvirEnvir ?

Exposure Infection Disease DeathRecovery DirectDirect Vaccination Poliomyelitis WHO/CSR EnvirEnvir Case management Rehabilitation ?

Global Eradication of Poliomyelitis Definition: Complete interruption of wild poliovirus transmission

Uses of surveillance How would surveillance help in achieving control objectives?How would surveillance help in achieving control objectives? How would it help in dealing with epidemic disease?How would it help in dealing with epidemic disease? WHO/CSR

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