About dynamics of infectious agents which tells it's epidemics...

1. DYNAMICS OF DISEASE
DYNAMICS OF DISEASE
TRANSMISSION
TRANSMISSION
Dr. Sanat Rathod
Assistant Professor
GMERS Medical College
Gotri
Vadodara

2. 2
2

3. 1st - The Infectious Agent
1st - The Infectious Agent
3
-any disease-causing
-any disease-causing
microorganism
microorganism
(pathogen)
(pathogen)
Infectivity
Infectivity
Pathogenicity
Pathogenicity
Virulence
Virulence

4. 2nd
: Source or Reservoir
• The starting point for the occurrence of a communicable
disease
• Source of infection
Source of infection :
• the person, animal, object or substance from which an
the person, animal, object or substance from which an
infectious agent passes or is disseminated to the host
infectious agent passes or is disseminated to the host
(immediate source)
(immediate source)
• RESERVOIR
RESERVOIR:
:
• “
“any person, animal, arthropod, plant, soil, or
any person, animal, arthropod, plant, soil, or
substance, or a combination of these, in which
substance, or a combination of these, in which
an infectious agent normally
an infectious agent normally lives and multiplies
lives and multiplies,
,
on which it
on which it depends primarily for survival
depends primarily for survival, and
, and
where it
where it reproduces
reproduces itself in such a manner that
itself in such a manner that
it can be transmitted to a susceptible host.
it can be transmitted to a susceptible host.
It is the natural habitat of the infectious agent.”
It is the natural habitat of the infectious agent.” 4

5. •5
Types of Reservoirs
Human
reservoir
Animal
reservoir
Non-living
reservoir

6. 6
cases carriers
carriers
•Clinical cases
(mild/severe-typical/atypical)
•Sub-clinical cases
•Latent infection cases
•Primary case
•Index case
•Secondary cases
Type
:
•Incubatory
•Convalescent
•healthy
Duration:
•Temporary
•Chronic
Portal of exit
:
•Urinary
•Intestinal
•Respiratory
•others

7. “A person in the population or
study group
Identified as having particular
disease, health disorder or
condition
Under investigation”
7

8. The clinical illness maybe mild or moderate,
typical or atypical, severe or fatal.
Epidemiologically, mild cases may be
more important sources of
infection than severe cases because they
are ambulant and spread the infection
wherever they go, whereas severe cases
usually confined to bed.
8

9. Subclinical cases
Subclinical cases
Inapparent, Covert, Missed or Abortive Cases
Inapparent, Covert, Missed or Abortive Cases
• disease agent multiply
multiply in the host but does
not manifest by S/S.
• But contaminates the environment in the
same way as clinical cases.
• Subclinical cases play a dominant role in maintaining the
chain of infection in the community.
9

10. subclinical cases
detected only by
detected only by
laboratory
laboratory
tests
tests
occurs in most
infectious disease.
Eg
 Rubella,
 Mumps,
 Polio,
 Hepatitis A and B,
 Influenza,
 Diphtheria
10

11. Latent infection
• infectious agent lies in a
in a non-infectious
non-infectious form-
form-
dormant
dormant within the host without symptoms
symptoms with
no shedding
shedding (and often without demonstrable
presence in blood, tissues or bodily secretions
of the host)
eg.
eg.
 HSV and VZV: nerve ganglia cells,
 CMV: kidney and salivary glands cells,
 EBV: lymphocytes
11

12.  Index Case
◦ Person that comes to the
attention of public health
authorities
 Primary Case
◦ First case of a communicable
disease introduced into the
population unit bring studied
◦ Attack rate
 Secondary Case
◦ Person who acquires the disease
from an exposure to the primary
case
◦ Secondary attack rate
12

13. Carriers
Carriers
 An
An infected person or animal
infected person or animal that
that harbors
harbors a
a
specific infectious agent in the
specific infectious agent in the absence
absence of
of
discernible (visible) clinical disease and
discernible (visible) clinical disease and
serves as a
serves as a potential source
potential source of infection to
of infection to
others
others
13
Reason :
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state.

14. Three elements in a carrier state:
Three elements in a carrier state:
14

15. CARRIERS
CARRIERS
As a rule carriers are less infectious than cases,
As a rule carriers are less infectious than cases,
but epidemiologically, they are more
but epidemiologically, they are more
dangerous than cases
dangerous than cases
because
◦ escape recognition
◦ continuing to live a normal life among population
or community
◦ readily infect the susceptible individuals
◦ over a wider area and longer period of time under
favorable conditions.
15

16. Incubatory Carriers:
Incubatory Carriers: those who shed the
infectious agent during the incubation period.
This usually occurs during last few days of IP
 Measles- the period of communicability is 4 days before the rash.
 Mumps- usually 4-6 days before onset of symptoms
 Polio- 7-10 days before onset of symptoms
 Hepatitis B- for a month before jaundice
 Pertusis
 Influenza
 Diphtheria 16
Classification of Carrier
Classification of Carrier

17. Carrier May Be Classified :
Carrier May Be Classified :
By Type
By Type
Convalescent Carriers:
Convalescent Carriers:
 those who continue to shed the disease agent during the
period of convalescence
 In the disease, clinical recovery does not coincide with
bacteriological recovery.
 Serious threat to HH members
 Highlights importance of bacteriological surveillance of
carriere state after recovery
◦ typhoid fever
◦ cholera,
◦ diphtheria,
◦ bacillary dysentery
◦ pertusis
17

18. Carrier may be classified :
Carrier may be classified :
BY TYPE
BY TYPE
Healthy Carriers:
Healthy Carriers:
victims of subclinical infection who have
developed carrier state without suffering from
overt disease, but are nevertheless shedding the
disease agent
◦ poliomyelitis,
◦ cholera,
◦ meningococcal meningitis,
◦ salmonellosis,
◦ diphtheria.
18
Note:- Person whose infection remains subclinical may or may not act as
carrier (eg.- in polio inf may remain subclinical but person act as temp carrier
due to shedding of virus in stool..while TB most of us with +ve Mt, do not
disseminate bacillie- so not labelled as carrier.

19. Temporary carriers
Temporary carriers are those who shed the
infectious agent for short period of time.
Chronic carriers
Chronic carriers are those who excretes the
infectious agent for indefinite periods
19

20. Chronic carriers
Chronic carriers
Chronic carriers are far more important sources of
infection than cases.
The longer the carrier state, the greater the risk of
community-- reintroduce disease into areas which
are otherwise free of infection
The duration of the carrier state varies with the
disease.
 In typhoid fever and hepatitis B, the chronic
carrier state may last for several years.
 In chronic dysentery it may last for year or longer.
 In diphtheria, the carrier state is associated with
infected tonsils, in typhoid fever with gall bladder
disease.
20

21.  Mary Mallon (1869 –1938), better
known as Typhoid Mary, was the
first person in the US identified as
an asymptomatic carrier of the
pathogen associated with
typhoid fever.
 She was presumed to have
infected some 50 people, three of
whom died, over the course of her
career as a cook.
 She was forcibly isolated twice by
public health authorities and died
after a total of nearly three
decades in isolation.
21

22.  Respiratory carrier: e.g. influenza
 Fecal (intestinal) carrier: e.g. typhoid, cholera
 Blood carrier: e.g. hepatitis B and HIV
 Urinary : e.g.Typhoid
 sexual Carrier: gonococcus and HIV
22
Carrier classified :
Carrier classified :
By Portal Of Exit of Infectious Agent

23. Animal reservoirs
Animal reservoirs
• infection that is transmissible under
natural conditions from animals to
man.
• e.g.
– Bacterial: Leptospira, plague from Rat.
– Viral : Rabies from dog.
– Protozoa: Leishmaniasis from dog.
– Helminths : Hydatid disease from dog
– Tape worms : Cattle , Pig.
•23

24. Reservoir in non-living
Reservoir in non-living
things
things
Some organisms are able to
Some organisms are able to
survive and multiply in
survive and multiply in
nonliving environments
nonliving environments
such as soil and water
such as soil and water
Clostridium that causes tetanus
Clostridium that causes tetanus
and botulism can survive many
and botulism can survive many
years in the soil
years in the soil
Hookworms deposit their eggs
Hookworms deposit their eggs
into the soil
into the soil
Water contaminated by human
Water contaminated by human
or animal feces cause GI tract
or animal feces cause GI tract
disease (list includes bacteria,
disease (list includes bacteria,
viruses, protozoa)
viruses, protozoa)
•24

25. 3rd - The Portal of Exit
3rd - The Portal of Exit
25
• Route of escape of the pathogen from
Route of escape of the pathogen from
the reservoir
the reservoir-IA enters into surrounding
env-transfer to host at their portal of entry
Examples:
respiratory secretions,
respiratory secretions,
GI
GI
blood exposure,
blood exposure,
breaks in skin
breaks in skin

26. 4th –Mode of Transmission
4th –Mode of Transmission
26
Direct
transmission
Indirect
transmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
•
Vector-borne
:
Air-borne
Fomite-born
Unclean hands
and fingers

27. Direct Transmission
Direct Transmission
•27

28. Direct Contact
•Inf spread by direct contact of
skin-skin, skin mucosa, mucosa-
mucosa of same or other person
•by touching, kissing,,
by touching, kissing,,
bites, or sexual intercourse
bites, or sexual intercourse
•Direct & immediate transfer of IA
from reserviour –host (no intermediate
agency)
•So it introduces larger dose of IA
•No time interval of survival in
environment..
•Overcrowded place or where
place with lack of ventilation
•28
Scabies
Pediculosis
STD’s
Skin/eye inf
leprosy

29. Droplet spread:
Droplet spread:
• Direct projection of
Direct projection of
droplets of
droplets of
saliva/nasopharynge
saliva/nasopharynge
al secretion by
al secretion by
Sneezing, Speaking,
Sneezing, Speaking,
Coughing
Coughing
• Droplets directly
Droplets directly
impinge on
impinge on
conjunctiva, nasal
conjunctiva, nasal
mucosa or skin
mucosa or skin
•29

30. •30
• H1N1
H1N1
• Tubercle bacilli
Tubercle bacilli
• Measles
Measles
• Chickenpox
Chickenpox

31. • Inoculation:
Pathogen injected into tissues.
– Tetanus spores
– Arboviruses (Insects).
•31

32. Vertical transmission
Vertical transmission
Transplacental
Transplacental
 To R C H
To R C H
 HIV
HIV
 HBV
HBV
•32
15

33. Indirect Transmission
5 ‘F’
33
food, flies, fomite, finger, fluid

34. Vehicle transmission
• Water: Cholera, H A V , H E V, Typhoid etc.
• FOOD:
FOOD: Staphylococci, Cl. Botulinum.
• Blood/serum-HIV, HBV,HCV
• Organ-cmv
34
 Clustering of cases
Clustering of cases
 Distance bw secondary cases more
Distance bw secondary cases more
 Common source can be traced
Common source can be traced

35. Mechanical
Hf
Diarrhea
Dysentery
Typhoid
Trachoma
Biological
Propagative
Only multiplication
No developmental
Plague bacilli in rat
flea
Cyclo propagative
Multiplication
developmental
Malaria parasites in
mosquito
Cyclodevelopmental
No multiplication
developmental
Filaria parasite
In mosquito
Vector-
insects
35

36. Trans-ovarian transmission
 Inf agent vertical transmitted from female
mosquito to her progeny
◦ Scrub typhus
◦ Rickettsial pox
◦ Indian tick typhus
◦ Q fever
◦ RMSF
Trans-stadial transmission-
Trans-stadial transmission-
Lyme disease, infects tick vector as a larva, and the
infection is maintained when it molts to a nymph and
later develops as an adult
36

37.  host feeding preference
 infectivity-ability to transmit disease agent
 susceptibility – ability to become infected
 survival rate of vectors in environment
 Domesticity
 Seasonal factors…
37

38. Fomites
Fomites:
:
Contaminated
Contaminated Nonliving Objects
Nonliving Objects like Cup, towel,
napkin, linen, Clothing, glass, Toys, Pencils, door handle,
surgical instruments, syringes, dressing materials…
Ex: Diphtheria,
Trachoma
influenza
scabies
38

39. 5th - The Portal of Entry
5th - The Portal of Entry
•39
-route through which the
-route through which the
pathogen enters its new
pathogen enters its new
host
host

40. Respiratory System
inhalatio
inhalatio
n
n
•40
Upper respiratory tract
Diphtheria
Lower respiratory tract
Tuberculosis

41. Gastrointestinal System
ingestion
ingestion
Fec
Feco-
o-Oral Route
Oral Route
Infectious agent excreted in faeces
& transmitted to the oral
portal of entry through
􀂃 contaminated food, water, milk,
drinks
􀂃 hands
•􀁺 Typhoid fever
•􀁺 Shigella
•􀁺 Cholera
•􀁺 Polio
•􀁺 Rotavirus
•􀁺 Hepatitis A, Hepatitis E
•41

42. Urinary & Reproductive
Tracts
S
e
x
u
a
l
S
e
x
u
a
l
c
o
n
t
a
c
t
c
o
n
t
a
c
t
•42
Gonorrhea
Syphilis
HIV

43. Breaks in Protective Skin
Barrier
•43
Percutaneous
Leptospirosis
Percutaneous
(bite of arthropod)
Yellow fever

44. 6th - The
6th - The Susceptible Host
Susceptible Host
44
A person or an animal that afford
A person or an animal that afford
lodgment to an infectious agent
lodgment to an infectious agent
under natural conditions.
under natural conditions.
•Accepts the pathogen
•The support of pathogen life & its
reproduction depend on the degree of the
host’s resistance.

45. •Cancer Patients
•HIV-AIDS Patients
•Transplant
Patients
•On steroids..
•Infant & Elderly
Patients 45

46. HOST
HOST
Obligate hos
Obligate host : the only host
Eg: Man in measles & typhoid
Primary /definitive
Primary /definitive host: in which
parasite attains maturity or passes
its sexual stage
Secondary or intermediate
Secondary or intermediate hosts:
the parasite is in a larval or asexual
state
•46

47. Life cycle
Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male / Female
Mosquito
Zygote
Ookinete
Oocyte
Salivary
Gland
Exflagellation

48. THE TIME INTERVAL BETWEEN INVASION BY
AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE
DISEASE IN QUESTION

49. DOSE OF INOCULUM
SITE OF MULTIFICATION
RATE OF MULTIFICATION
HOST DEFENCE MECHANISM

51. 0
5
10
15
Time
1
2
3
50% 50%
Probable exposure
Median incubation time
No of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22

52. Period From Disease Initiation To
Period From Disease Initiation To
Disease Detection
Disease Detection
For NCDs
For NCDs

53. 0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIME
GENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF
INTERVAL OF TIME BETWEEN RECEIPT OF
INFECTION BY A HOST AND MAXIMAL
INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOST
INFECTIVITY OF THAT HOST

54. THE GAP IN TIME BETWEEN
THE ONSET OF THE
PRIMARY CASE AND THE
SECONDARY CASE

55. It is defined as the time during which
an infectious agent may be transferred
directly or indirectly from an infected
person to another person, from an
infected animal to man , or from an
infected person to an animal, including
arthropods

56. 64%
11
4
7
76%
13
3
10
Attack
Rate
Total
Well
Ill
Attack
Rate
Total
Well
Ill
Did not eat the food (not exposed)
Ate the food (exposed)
Attack Rate = Ill / (Ill + Well) x 100 during a time period
Attack rate = (10/13) x 100 = 76%
( 7/11) x 100 = 64%

57. It is defined as the number of exposed
It is defined as the number of exposed
persons developing the disease within the
persons developing the disease within the
range of the incubation period, following
range of the incubation period, following
exposure to the primary case
exposure to the primary case

58.  Used to estimate to the spread of disease in a
Used to estimate to the spread of disease in a
family, household or other group environment.
family, household or other group environment.
 Measures the infectivity of the agent and the
Measures the infectivity of the agent and the
effects of prophylactic agents (e.g. vaccine)
effects of prophylactic agents (e.g. vaccine)
58
SAR (%)
Total number of cases – initial case(s)
Number of susceptible persons in the group –
initial case(s)
= x 100

59. Thank You
Thank You