Presentation from Dr. Akhilesh Bhargava

1. Dynamics of Disease
Transmission
Dr. Akhilesh Bhargava
MD, DHA, PGDHRM
Prof. Community Medicine
&
Director-SIHFW, Jaipur

2. E
Transmission-prerequisites
A H
• Agent
• Source for agent
• Portal of exit from host
• Suitable mode of transmission
• Portal of entry suitable to agent
• Susceptible host
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3. Chain of Transmission Mode
Eyes
Nose
Mouth
Skin
Urinary tract
Genital tract
Agent
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4. Modes of Spread
vDirect
ü Contact
üEnsures certainty
üLarger dose,
üLess chances of organism dying
outside human host
ü Airborne
ü Droplet (3-5 microns), Distance 1-2 feet
ü Droplet Nuclei (< 3 microns) Distance 3-5
feet
ü Infected dust
ü Transplacental
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5. vIndirect
v vehicles
üWater
üFood
üMilk
üBlood and plasma
üOrgans
ü Number of case dependent on dose of infection in
vehicle
ü Cases confined to exposed population
ü Large Geographic spread
ü Cases start disappearing with vehicle control
ü Common source is traceable
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6. ü Vectors
üMechanical
üBiological
üCyclo- propogative (change in
form &number)
e.g. Plague bacilli in Rats
üCyclo- developmental (Change
in form)
e.g. Malarial parasite in mosquito
üPropogative (Change in
number)
e.g. Microfilaria in mosquito
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7. Herd Immunity
• Resistance of a group to an attack by a
disease to which a large proportion of
the members of the group are immune
• If a large % of population is immune Þ
entire population is protected, not just
those who are immune
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8. Herd Immunity
• Why?
– If a large % of population is immune
then likelihood is small that an
infected person will encounter a
susceptible person and transmit the
infection
• More of the encounters will be with other
immune people
• Important for immunization
programs
– Do not need 100% coverage
immunization rates
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9. Herd Immunity
Necessary conditions:
– Disease agent must be restricted to a
single host species within which
transmission occurs
– Transmission must be relatively direct
from one member of the host species
to another
– Infections must induce solid immunity
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10. Herd Immunity
• Works when:
– Probability of an infected person
encountering every other individual in the
population (random mixing) is the same
• Does NOT work when:
– An infected person interacts only with
people who are susceptible (no random
mixing); likely to transmit the disease to
those people
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11. How to Prevent & Control
Diseases ?
• Individual patient level
– Counseling
– Screening
– Treatment
• Community level
– Surveillance
– Targeted measures
• Agent
• Environment
• Host
• Route of transmission
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12. Basic Control Strategies
• Substitution
• Treatment
• Isolation
• Shielding
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13. New com pound
• Substitution or Process
Agent
Usually applicable where
Physical / Chemical / Nutritional
agents are involved
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14. Treatment with
chem icals / Sterilization
• Treatment Antibiotic use
Agent
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15. • Isolation
Agent
Disinfection/ Sterilization
Universal Precautions
Vector control
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16. Boosting immune
system-Vaccination
• Shielding Repellents
Housing
Behavioral
modifications
Agent
Chemoprophylaxis
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17. Prevention & control…
Blocking Transmission
• Food Hygiene
• Water Treatment
• Vector Control
• Personal Hygiene
• Sterilization & Disinfection
• Environmental Engineering
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18. Prevention & Control:
Targeted Strategies
Targeted at Reservoir (Human Host)
• Early Diagnosis
• Notification
• Isolation
• Surveillance
• Quarantine
• Disinfection
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19. Targeted at Route of transmission
– Direct spread
• Contact tracing (TB, HIV)
• Air quality monitoring
• Reducing air microbial density
• Avoid overcrowding, improving ventilation
• Personal behavior-safe sex, lifestyle advice)
• Isolation/quarantine
– Indirect spread
• Environmental control (proper food handling;
water processing)
• Safeguarding blood supply
• Vector control (pest control)
Direct spread through Air borne transmission (Droplet) is
difficult to control in general population
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20. Targeted at Susceptible
Host
• Immunization
• Chemo- prophylaxis
• Physical barriers-
»Mosquito nets
»Clothing
»Housing
• Improving Quality of life
• Behavioral
• Diet/exercise
• Smoking/ Alcohol
• Hygiene practices
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21. Targeted at Agent
In the environment
Radiation
Sterilization
Antiseptics
Incineration
In Human beings
Prompt Diagnosis and Treatment of
patients with drugs e.g. Antibiotics
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22. Targeted at Environment
– Early Diagnosis
• Lifestyle & behavior (e.g.
breastfeeding)
– Health services
• Policy (notification, contact tracing)
• Adequate provision for prompt
Diagnosis & Treatment
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23. – Legislation
• Food hygiene (PFA Act)
• Air-
– The Air (Prevention & Control of Pollution) Act,
1981
• Water supply
– The Water (Prevention & Control of Pollution)
Act, 1974
• Sanitation
– The Environment protection Act, 1986
– The National Environmental Tribunal Act,
1995
– The Bio-medical waste (Management &
Handling Rules), Act, 1998
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