DYNAMICS OF DISEASE & DISEASE TRANSMISSION

1. Natural history of disease,
Dynamics of disease
transmission
Dr. Vanitha,
Assistant Professor,
Dept. of Community Medicine
SRMC & RI

2. CONCEPTS OF DISEASE
 DISEASE: physiological / psychological
dysfunction. Spectrum of disease-many shades ranging
from in apparent sub-clinical cases to severe illness
 ILLNESS: subjective state of the person, who
feels aware of not being well.
 SICKNESS: state of social dysfunction (i.e)
sickness role
 Natural history of disease - Process of disease/
condition progression from the time it affect an
individual to the time the individual recovers or
dies if appropriate measures are not taken 2

3. THEORIES OF DISEASE
 SUPERNATURAL THEORY OF DISEASE
 THEORY OF SPONTANEOUS GENERATION
 YANG-YIN PRINCIPLE
 CONCEPT OF CONTAGION
 MIASMATIC THEORY
 GERM THEORY
 EPIDEMIOLOGICAL TRIAD
 MULTIFACTORIAL CAUSATION
 WEB OF CAUSATION
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4. NATURAL HISTORY OF DISEASE
PRE-PATHOGENESIS PHASE:
 Preliminary to the onset of disease
 Disease agent hasn’t yet entered the human body
 Interaction between AGENT, HOST &
ENVIRONMENT
 Creates favourable platform for disease occurance
PATHOGENESIS PHASE:
 Starts with agent’s entry into the susceptible host
 Disease agent multiplies in the host
 Causes series of physiological changes in the host
 Leads to either- RECOVERY, Disability ,Death
4

5. Balance is
Disturbed.
Pathological
Process have
Still not
started
Pathological
Process has
Started With
out signs /
symptoms.
detection by
screening
Disease
can be
easily
diagnosed.
Disease _
diagnosed by
cl.Specialist/
/ equipment.
Mild Signs
/Symptoms
seen.

6. Epidemiological
Triad
Agent
Host Environment
Determinants -
Epidemiology
Agent factors
Host factors
Environmental factors

7. Epidemiology
Host factors
 sex
 race
 genetic makeup
 Immunity
 Age
 Physiological state
 nutritional state etc
Agent factors
Infective agents
Nutritional agents
Carcinogens
Allergens
Others
Environmental Factors
Physical
Biological
Socio economical

8. Agent factors -. living or non- living.
 Biologic agents: living agents, e.g., viruses,
bacteria, fungi, protozoa, etc ….found in the
reservoir of infection(man, animal, insect, soil).
 Nutrient agents: proteins, fats, carbohydrates,
vitamins, minerals and water
 Physical agents: heat, cold, pressure, radiation,
electricity.
 Chemical agents: metals (e.g., lead). Fumes,
dusts, gases.
 Mechanical agents: Chronic friction and other
mechanical forces may cause trauma/ injuries

9. Host factors
 Age: Certain diseases are more frequent in certain age
groups-measles in childhood, atherosclerosis in old age.
 Sex-DM more frequent in females; heart disease in males.
 Heredity: Harmful genes in the constitution may give
rise to disease, e.g. haemophilia, colour blindness, albinism
 Nutrition: Poor nutrition - kwashiorkor, anaemia.Over-
eating - obesity and diabetes.
 Occupation: Occupation of the host may predispose to
certain diseases, e.g., lead poisoning, silicosis, accidents.
 Customs and habits: Smoking related to oral &lung
cancer; open air defecation, by causing soil pollution,
favours the spread of intestinal parasites.
 Human behaviour: Lack of physical exercise, alcohol and
certain drugs affect health. 10

10. 11

11. Environmental Factors
Physical
 Air ,water, soil
 Light , poor housing
 sound
 Heat
 Ionizing/Non-ionizing
radiation
Biological
 Domestic animals
 Wild animals
 Other reservoirs , vectors
Socio-economical
Habits,
Culture,
Religion,
Customs,
behavior,
Lifestyle,
Family size & composition,
Overcrowding,
Occupation,
Income & social status

12. GRADIENT OF INFECTION
 Range of manifestations occuring in the host as a result of the
infection
 Biological gradient
INAPPARANT INFECTION
MILD ILLNESS
CLINICAL DISEASE
SEVERE ILLNESS
DEATH
12

13. GRADIENT OF INFECTION
INAPPARANT INFECTION
MILD ILLNESS
CLINICAL DISEASE MEASLES
CHICKEN POX
SEVERE ILLNESS
DEATH
13

14. GRADIENT OF INFECTION
INAPPARANT INFECTION
MILD ILLNESS
CLINICAL DISEASE
SEVERE ILLNESS
RABIES
DEATH
14

15. GRADIENT OF INFECTION
INAPPARANT INFECTION
MILD ILLNESS POLIO
HEPATITIS
CLINICAL DISEASE INFLUENZA
SEVERE ILLNESS
DEATH
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16. DYNAMICS OF TRANSMISSION
 Effective disease transmission has 3
components
 SOURCE or RESERVOIR
 MODES OF TRANSMISSION
 SUSCEPTIBLE HOST
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17. CHAIN OF INFECTION
SOURCE (or)
RESERVOIR
MODES OF
TRANSMISSION
SUSCEPTIBLE
HOST
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18. SOURCE
 THE PERSON/ ANIMAL/ SUBSTANCE FROM
WHICH THE INFECTIOUS AGENT PASSES TO
THE HOST
 Immediate source of infection
 E.g.- contaminated food,
water, milk or soil

19. RESERVOIR
 Any person/ animal/ plant/ soil/ substance in
which the infectious agent lives & multiplies, on
which it depends primarily for survival and
where it reproduces itself in such a manner,
that it can be transmitted to a susceptible host
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20. TYPES OF RESERVOIR
 HUMAN RESERVOIR
 ANIMAL RESERVOIR
 RESERVOIR IN NON LIVING THINGS
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21. TYPES OF RESERVOIR
 HUMAN RESERVOIR -CASES
-CARRIERS
 ANIMAL RESERVOIR
 RESERVOIR IN NON LIVING THINGS
21

22. TYPES OF RESERVOIR
 HUMAN RESERVOIR -CASES CLINICAL
ILLNESS
SUBCLINICAL
CASES
LATENT INFECTION
-CARRIERS
 ANIMAL RESERVOIR
 RESERVOIR IN NON LIVING THINGS 22

23. TYPES OF RESERVOIR
 HUMAN RESERVOIR -CASES
-CARRIERS TYPE
DURATION
PORTAL OF
EXIT
 ANIMAL RESERVOIR
 RESERVOIR IN NON LIVING THINGS 23

24. TYPES OF RESERVOIR
 HUMAN RESERVOIR
 ANIMAL RESERVOIR ZOONOSES
 RESERVOIR IN NON LIVING THINGS

25. TYPES OF RESERVOIR
 HUMAN RESERVOIR
 ANIMAL RESERVOIR
 RESERVOIR IN NON LIVING THINGS
SOIL, INANIMATE MATTERS
e.g., tetanus, anthrax,
mycetoma 25

26. MODES OF TRANSMISSION
DIRECT TRANSMISSION
 DIRECT CONTACT
 DROPLET INFECTION
 CONTACT WITH SOIL
 INNOCULATION INTO SKIN
 VERTICAL TRANSMISSION 26

27. MODES OF TRANSMISSION
INDIRECT TRANSMISSION
 VEHICLE BORNE
 VECTOR BORNE
 AIR BORNE
 FOMITE BORNE
 UNCLEAN HANDS AND FINGERS 27

28. MODES OF TRANSMISSION
INDIRECT TRANSMISSION
 VEHICLE BORNE MILK- Qfever, brucellosis
WATER/ FOOD- cholera, typhoid, AGE
BLOOD- malaria, hep B, syphilis
 VECTOR BORNE
 AIR BORNE
 FOMITE BORNE
 UNCLEAN HANDS AND FINGERS
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29. MODES OF TRANSMISSION
INDIRECT TRANSMISSION
 VEHICLE BORNE
 VECTOR BORNE Vector
By transmission chain
Based on transmit methods
Propagation
 AIR BORNE
 FOMITE BORNE
 UNCLEAN HANDS AND FINGERS
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30. MODES OF TRANSMISSION
INDIRECT TRANSMISSION
 VEHICLE BORNE
 VECTOR BORNE
 AIR BORNE Droplet nuclei - TB, flu,
measles
Dust – Nosocomial infection
 FOMITE BORNE
30

31. MODES OF TRANSMISSION
INDIRECT TRANSMISSION
 VEHICLE BORNE
 VECTOR BORNE
 AIR BORNE
 FOMITE BORNE Soiled clothes, toys
Eg: diptheria, dysentry, typhoid
 UNCLEAN HANDS AND FINGERS 31

32. MODES OF TRANSMISSION
INDIRECT TRANSMISSION
 VEHICLE BORNE
 VECTOR BORNE
 AIR BORNE
 FOMITE BORNE
 UNCLEAN HANDS AND FINGERS Dysentry,
staph inf.

33. SUSCEPTIBLE HOST
 Disease transmission – not occur without presence of susceptible
host.
 For the parasitism to be successful, these 4 stages has to occur
Portal of entry
Site of election ( optimum site for its survival &
multiplication)
Portal of exit
survival in the external environment
(until to find a new host to propagate its species)
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34. HERD IMMUNITY
Resistance of a group to an attack by a disease, to which, a
large proportion of population are immune.
1. Why does Herd immunity occur:
If a large group of the population is
immune to a particular disease, then the probability that an
infected person encountering a susceptible host is less.
2. Why it is important: For immunization purposes.
3. Criteria for Herd immunity:
* Single host species
* Direct transmission
* No reservoir
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35. DISEASE CYCLE
FASTIGIUM
PRODROME
INCUBATION
DEFERVESCENC
E
CONVALESCENCE
DEFLECTION
POINT OF
INVASION
PRODROMAL
POINT
DIFFERENTIAL
POINT
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36. Disease cycle
Stages in course of the most communicable diseases
 Incubation period: Time interval between the entry of
the disease agent in the body and
manifestation of clinical signs and symptoms.
 Prodromal period: Ranging from 1 to 4 days, and is
marked by vague signs and symptoms. Clinical
diagnosis is usually not possible.
 Fastigium:Represents height of the disease. Signs
&symptoms are clear-cut. Patient is confined to bed
 Defervescence: Patient begins to feel better; the body
defenses (immunity) begin to respond.
 Convalescence-Patient’s recovery is established;
 Defection: The patient recovers from illness.

37. Definitions
 Epidemic: (Epi = upon; demos = people). An
outbreak of disease in a community in excess of
"normal expectation
 Endemic: (En = in; demos = people).Constant
presence of disease within a geographic area, or
the usual prevalence of a given disease in a
particular area.
 Sporadic: The incidence at intervals of single,
scattered cases of disease, e.g., polio. A sporadic
may be the starting point of an epidemic.
 Pandemic: (Pan= all; demos= people). An
epidemic which spreads from country to
country or over the whole world,

38. Iceberg phenomenon of disease.
Disease in a community – be compared with an
iceberg. The floating tip of iceberg represents what the
physician sees in the community, i.e., clinical cases.
Vast submerged portion of iceberg represents - hidden
mass of disease - Iatent, inapparent, presymptomatic,
undiagnosed cases and carriers in community
"waterline" represents the demarcation between
apparent and inapparent disease. - HT, diabetes,
anaemia, mental illness) the unknown morbidity (i.e.
the submerged portion of iceberg) far exceeds the
known morbidity.
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39. The hidden part of the iceberg thus constitutes an important,
undiagnosed reservoir of infection or disease in the community,
and its detection and control is a challenge in modern
techniques in preventive medicine.
Iceberg phenomenon of disease.
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40. THANK YOU