This document provides definitions and information about communicable diseases (CD) and their transmission. It begins with learning objectives and then defines key terms related to CD and transmission. It discusses how CD can be classified based on causative organisms, clinical presentation, or body system affected. The document also covers reservoirs of infection, the chain of disease transmission including the six steps, and effects of agents on hosts. It provides examples of reservoirs including humans, animals, and the environment.

1. CDC FOR BSC NURSING
BY GUGS A NEMERA
1BY GN 2013

2. Learning objective
At the end of the session students will be able to:
• clearly differentiate between CD and NCD
• Define at least five terms those commonly used in CD
and relate it to practical situations
• Discuss CD
2BY GN 2013

3. UNIT ONE
INTRODUCTION
Disease can be communicable or non
communicable
Communicable disease in turn classified into
several divisions based on
causative organisms
clinical presentation or system of body affected
This classification is valuable for
Clinician
Microbiologists
Epidemiologists
Parasitologsts .
3BY GN 2013

4. INTRODUCTION CONT’D
Communicable continues to remain a leading
cause of morbidity, disability and mortality
worldwide.
It accounts for one tenth of deaths in rich
countries and six out of ten deaths in poorer
countries .
for instance annually worldwide
2 m deaths occurs from diarrhea
4 m die of LRTI
700,000 die from measles
2 m die from TB
90% from developing countries
4BY GN 2013

5. Definition of common terms
(important terms)
Carrier- A person that carries a specific infectious
agent and can transmit to others but has no clinical
sign of infection.
Case - A person identified as having specific health
problem or disease of interest
Case definition- standard criteria for deciding whether
a person has particular disease or health problem.
5BY GN 2013

6. Chain of disease transmission: is a logical sequence
of factors or links of a chains that are essential for
development of the infectious agent and progression
of disease
Chemoprophylaxis- Administration of drug to
prevent the development or progression of an
infection to actual disease
Mass chemoprophylaxis
Selective chemoprophylaxis 6
Definition of common terms cont’d
BY GN 2013

7. Chemotherapy: Use of chemicals to treat a
clinically manifest disease
Assignment
Write at least 250 chemotherapeutic agent those
commonly used in Ethiopia
S.No Drug Dose Route Frequency Duration Indication
1
2
250
Definition of common terms cont’d
7BY GN 2013

8. Communicable period: the time during which an
infectious agent may be transferred directly or
indirectly from infected person to susceptible host
Contact - A person or animal that has had an
opportunity to acquire the infection following
association with infected person, animal or
contaminated environment
8
Definition of common terms cont’d
BY GN 2013

9. Control /Containment – Operation aimed at
reducing the prevalence of the disease to a level
where it is not a major public health important.
Disinfection: the killing of infectious agents
outside the body by direct exposure to physical
or chemical agents.
Sterilization – distraction of all forms of life by
heat, irradiation, gas or chemical treatment.
Definition of common terms cont’d
9BY GN 2013

10. Contamination :The presence of an infectious agent
on the body surface or other inanimate articles or
substances
Note: contamination on body surface does not
imply carrier state
 Drug resistance – The ability of infectious agent to
survive despite the administration of antimicrobial in a
dose equal to or higher than the usual recommended
dose 10
Definition of common terms cont’d
BY GN 2013

11. Disinfection- the killing of infectious agents outside the body
by direct exposure to physical or chemical agents.
Concurrent disinfection→ application of disinfective
measure as soon as possible of the discharge of infectious
material from the body of an infected person or after the
soiling of material with such infectious discharge.
Terminal disinfection → is the application of disinfective
measures after the pt. has been removed by death or to
hospital, isolation or other partice has been discontinued
11
Definition of common terms cont’d
BY GN 2013

12. Sterilization – distraction of all forms of life by heat,
irradiation, gas or chemical treatment.
Disinfestations – The procedure of destroying or
removing undesired small forms of animals
particularly arthropods, rodents, present up on the
person, clothing or in the environments of an
individual or domestic animal using chemicals or
physical agents.
12
Definition of common terms cont’d
BY GN 2013

13. Elimination – eradication of disease from large
geographical region or political jurisdiction.
Endemic – Continuous presence (usual prevalence)
of a disease or infectious agent with in a
geographical area.
Epidemic or outbreak- occurrence of cases of an
illness with the frequency that is clearly in excess of
what is expected in a given region therefore
demanding emergency control.
Definition of common terms cont’d
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14. Epidemic Thresh hold- The minimum number of
cases indicating the beginning of an out breaks.
Eradication-Termination of all transmission of
infection through surveillance and control.
Host- A person or other living animal that
accommodates infectious agent under normal
conditions.
Definition of common terms cont’d
14BY GN 2013

15. Immune individual – A person or animal that has
specific protective antibody and/or cellular immunity
as a result of pervious exposure /infection,
immunization.
Immunity – resistance usually associated with the
presence of antibodies
Immunogenicity: -The ability of an agent to produce
specific immunity.
15
Definition of common terms cont’d
BY GN 2013

16. Exposure – meeting with an infectious agent in the way
that may cause disease.
Illness: -Individual or subjective feeling of discomfort.
Disease: -A state of physiological and psychological
dysfunction.
Incubation period – The time interval from the time of
infection to the time of appearance of clinical
manifestation
16
Definition of common terms cont’d
BY GN 2013

17. Infection – The entry and development of an infectious
agent in the body of humans or animals.
Nosocomial infection → An infection occurring in
patient in hospital and other health facility in whom the
infection was not present or incubating at time of
admission or residual of infection during previous
admission.
Community acquired infection – infection that occurs in
the community (general population.)
Definition of common terms cont’d
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18. Infectious agent – Bacteria, viruses, Fungi or parasites or
their products that can cause disease.
Infectious individual: A person or an animal from which
the infectious agent can be naturally acquired.
Infestation- The lodgement, development and
reproduction of arthropods on the surface of the body or
in the clothing. This also used for invasion of the gut by
parasitic worms.
Inoculums size – The minimum size of infectious agent
or its products that can cause disease. 18
Definition of common terms cont’d
BY GN 2013

19. Isolation – Keeping infected persons or animals in
separate place for as long as they can transmit
disease
Strict isolation
Contact isolation
Respiratory isolation
TB. Isolation.
Enteric precaution
Drainage /secretion precautions-
19
Definition of common terms cont’d
BY GN 2013

20. Primary or index case- A person who acquires a disease
through exposure and brings it in to population
Notifiable disease – disease for which regular, frequent
and timely information on individual cases is considered
necessary for prevention and control of disease.
Notification – The processes by which cases or out
breaks one brought to the knowledge of the health
authorities.
20
Definition of common terms cont’d
BY GN 2013

21. Quarantine- Restriction of the activity of well
person or animal who have exposed to a case
of communicable disease during its periods of
communicability.
Definition of common terms cont’d
21BY GN 2013

22. Mode of Transmission- any mechanism by
which infectious agent spread from source or
reservoir to a person.
Pollution – The presence of offensive, but not
necessarily infectious matter in the
environment
22
Definition of common terms cont’d
BY GN 2013

23. Reservoir- Any person, animal, arthropod, plant, soil
etc in which the infectious agent normally lives and
reproduce itself in such a manner that it can be
transmitted to a susceptible host.
Secondary case – A person infected by primary case.
Surveillance- Systematic collection, collation and
analysis of data, dissemination information for
action.
23
Definition of common terms cont’d
BY GN 2013

24. Susceptible host- person or animal not possessing sufficient
resistance against particular infectious agent to prevent
contracting infectious disease when exposed to it.
Transmission: any mechanism by which infectious agent
spread from source or reservoir to a person.
 Direct transmission – immediate transfer of infectious agent to a
suitable portal of entry (direct contact, projection)
 Indirect transmission- transfer of infectious agent through
intermediate means (vehicle born, contaminated materials vector
born)
24
Definition of common terms cont’d
BY GN 2013

25. Transmission cycle -is a cycle which describes
how an organism grows, multiplies and
spreads. In some cases man may be the only
host in which case the infection spreads
directly from man to man. E.g. measles. In
some cases like malaria the transmission cycle
involves man and mosquito
25
Definition of common terms cont’d
BY GN 2013

26. Absolute or complete quarantine, the
limitation of freedom of movement of those
exposed to a communicable disease for a
period of time not longer than the longest
incubation period of that disease in such
manner as to prevent effectual contact with
those not so exposed.
26
Definition of common terms cont’d
BY GN 2013

27. Modified quarantine: A selective partial
limitation of freedom of movement of
contacts commonly on the bases of known or
presumed differences in susceptibility and
related to the longer of disease transmission
27
Definition of common terms cont’d
BY GN 2013

28. Universal precaution – Simple standard procedure to be used
during care of patients at times to minimize the risk of
transmission.
Virulence – The ability of infectious agent to invade and
damage the tissue of the host and cause death.
Zoonoses – An infectious disease that is transmissible under
normal condition from animal to human.
Zonosis – An infection or infectious disease that is
transmissible under normal condition from vertebrate to
human.
Definition of common terms cont’d
28BY GN 2013

29. Sporadic - A disease that occur in a
population in occasional and irregular
intervals.
Pandemic – worldwide epidemic disease.
29
Definition of common terms cont’d
BY GN 2013

30. COMMUNICABLE DISEASE/ (infectious disease)
Definitions
A disease due to specific agent or its toxic products
that a rises through transmission of that agent or its
products from infected person, animal or reservoir to
susceptible host either directly or indirectly through an
intermediate plant or animal host, vector or
intermediate environment
30BY GN 2013

31. Specific feature of communicable disease
A case may be risk factor
Each infectious disease has its own incubation period
People may be immune
An individual may be a source without being recognized as a
case.
There is some times a need for urgency
Preventive measures (usually) have a good scientific ground
Intervention in infectious disease can have several effects
31BY GN 2013

32. Classification of communicable disease
It may be classified in several ways i.e. by
Clinical manifestation
Time course
Taxonomy of infectious agent
Mode of transmission
32BY GN 2013

33. Based on C/m or system involved
Diarrhoeal disease
Febrile illness
Respiratory tract infection
Central Nervous system infection
Cardiovascular system infection
UTI
Cutaneous
33BY GN 2013

34. Based on time course
Acute
Disease with short duration
needs urgent care
Rapidly progressive
Abrupt on set.
Chronic
 Indicate duration usually
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35. Based on taxonomy of infectious agent
Metazoan
Protozoal
Bacterial
Fungal
Viral
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36. Based on mode of transmission
¨ Airborne diseases (respiratory tract as portal of entry and/or exit)
¨ Feco-oral transmitted diseases (GIT as entry and/or exit)
¨ Direct contact (Mucus membranes and/or skin as portal of entry /exit)
¨ Direct inoculation
¨ Vector bone disease
¨ Inoculation by bite of animal/ contacts with
animal products ( zoonosis ).
36BY GN 2013

37. Unit two:
Chain of disease transmission (diseases
transmission dynamics)
37BY GN 2013

38. Learning objective
At the end of the session students will be able to:
1.Describe Chain of disease transmission
2.List major effects of agent on the host
38BY GN 2013

39. Chain of disease transmission
Definitions
A logical order of events which must occur in
order for disease causing organisms to cause
infection.
Series that is essential to the development of
the infectious agents and propagation of
disease.
There are six successive events implicated in
the chain of disease transmission
39BY GN 2013

40. Chain of disease transmission cont’d
40BY GN 2013

41. 1.Infectious Agent
• It can be an organism or its toxin
• Infection agents’ needs
Multiplication
Survival
Reservoirs
Persistence
Latency
Vector
Intermediate host
41BY GN 2013

42. Multiplication→ two methods
– Asexual (almost exact replicas produced →any
natural selection occur on the batches than single
individual.
– Sexual- scope of variety are there
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43. Survival
Agent survive by finding suitable hosts
Agent prolong the period of survival by different
methods
Reservoirs
Suitable place to store infectious agent
Reservoir can be humans, animals, vectors or
inanimate environment (soil, waters)
Persistence
–Development of special stages by agent to with
stand distraction in adverse environment. E.g. forming
cyst (protozoa), eggs (nematodes) spore (bacteria)
• 43BY GN 2013

44. Latency
–Developmental stage in the environment not
Infective to a new host.
–Parasite time of suitable condition
Vector
–Parasite use service of arthropods to transmit from
one host to other
– It can be part of transmission process (Mosquito)
Intermediate host
– some parasite needs intermediate host for
development before they invade the final host.E.g.
Schistosoma uses a molluscan 44BY GN 2013

45. Effect of the agent on host
If enough agents survive to infect a new
host, they will produce a reaction or
illness.
The effect of host is determined by
Virulence
Toxicity
Dose response
45BY GN 2013

46. 2.Reservoir of infection
A living or non living in which an infectious
agent normally lives, transforms and
multiplies on which it primarily for survival
and where it produce itself in such a way that
it can be transmitted to new susceptible host.
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47. Types of reservoir
A. Man as the only reservoir
Measles
Gonorrhoea
Syphilis
Small pox
Typhoid
Meningococcal meningitis
Transmission cycle man to man
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48. Types of reservoir cont’d
B. Animals as reservoir
Infectious disease where animals are primary
reservoirs includes:
Bovine Tuberculosis – Cow to man
Brucellosis – Cows, pigs and goats to man
Anthrax – Cattle, sheep, goats, horse to man
Rabies - Dogs, foxes, wild animal to man
Man is not essential part (usual reservoir) of
the life cycle
48BY GN 2013

49. Types of reservoir cont’d
C .Non living thing
Some of the organisms are basically saprophytes i.e.
living in soil adapted to live freely in nature and
biologically equipped to withstand marked
environmental changes.
Some of the non living reservoirs are soil, water, food
etc
Examples
Clostridium tetani of tetanus
Salmonella typhi of Typhoid fever
49BY GN 2013

50. 3.Portal of exit
¨ Site on reservoir through which an infectious
agent escapes from the reservoir.
¨ Examples
GIT – Typhoid fever, Ascariasis dysentery
Skin and mucus membrane-syphilis
RT – TBC
50BY GN 2013

51. 4.Made of transmission
Mechanism by which an infectious agent
transferred from reservoir or infected host to
new host.
 Two main type of mode transmission
1. Direct transmission
2. Indirect transmission
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52. Direct transmission
Immediate transfer of infectious agent from
infected host or reservoir to an appropriate
portal of entry on the susceptible host.
Some of the ways of direct transmission are
Direct vertical – transpalcental syphilis, HIV
Direct contact – contact of if IA with skin, mucosa,
Conjunctiva
Direct touching, kissing, sexual intercourse
Direct projection – droplets of saliva created by
expiratory activity
52BY GN 2013

53. Indirect Transmission
Airborne transmission
Vehicle Borne transmission
 Vector borne transmission
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54. 5.Route of entry
 Site on susceptible host through which an
infectious agent get into it
 The manner of entry is one of the factors
which determine whether or not the
infectious agent establishes the infection
54BY GN 2013

55. 6.Susceptible host-
A person or animal lacking of sufficient
resistance to particular pathogenic agent to
prevent the disease if or when exposed.
In order for transmission to be completed, the
existence of susceptible host is necessary
55BY GN 2013

56. Level of susceptibility of depends on;
Nutritional status
Stress
Environment
Pre-existing medical condition
Immune status
Age
56BY GN 2013

57. Unit three
Determinants of disease and defence
mechanism of hosts
57BY GN 2013

58. Learning objective
• At the end of the session the learner will be
able to:
1.Describe major determinants of health using
epidemiological triad
2.Discuss the defense mechanism of the host
58BY GN 2013

59. 4.1: determinants of disease
The determinants of disease presented by
simply by Epidemiologic triad of host, agent
and environment
Host factors
Demographic
Biological
socioeconomic
Agent factors
 Biological agents
Physical agents
Chemical agents
 Nutrient agents
Mechanical agents
Social agents
Environment:
Physical environment
Biological environment
Social environment
59BY GN 2013

60. 4.2 Defence mechanism of the host
1. Non specific resistance or innate or natural
immunity.
2. Immune system defences
60BY GN 2013

61. Non specific resistance or innate or natural
immunity.
Are immunity used for either to prevent micro
organisms from entering the body or to
eliminate them rapidly
 It includes
A. Physical barrier
B. Chemical (secreted) barrier
C. Inflammatory cells or action of white blood cells
D. Inflammatory response
61BY GN 2013

62. Physical barrier
External barrier (skin & epithelial tissue)
Internal barrier (mm)
Prevent the pathogen from entering to body.
Filtering and clearing the pathogen – cilia &
sneeze reflex
62BY GN 2013

63. Chemical (secreted) barrier
acid in stomach, enzymes in the tear and
saliva ,substances in sebaceous and sweat
secretion act non specifically for bacteria,
fungus
interferon for virus
63BY GN 2013

64. Inflammatory cells or action of white blood cells
Acting as phagocyte e.g. Monocyte and
macrophages.
Inflammatory response
The major function of natural immunity
elicited in response to tissue injury or invading
organism
64BY GN 2013

65. Immune system defences
The body has three means of defending itself
when the body invaded by agents.
 1st
line defence
 2nd
line of defence
 3rd
. line of defence
65BY GN 2013

66. 1st
line defence
The phagocytic immune response involves WBC
(granulocyte and macrophage)
Move to the point of attack and engulf and destroy the
invading agent
2nd
line of defence
The humeral response sometimes called antibody
response
A class of protein which all anti body belong is called IG
Antibodies are produced by a class of lymphocyte called
B.cells
3rd
. line of defence (cellular immune response)/Cell mediated
immune response
 Deals primary with intera-cellular pathogens
 It also involves lymphocyte
66BY GN 2013

67. Unit four
Host parasite interactions (measuring of infectiousness)
67BY GN 2013

68. Learning objective
• After completion of this session students will
be able to
1.List common measures of infectiousness of CD
68BY GN 2013

69. 1 Infectivity
 Ability of the infectious agent to invade and
multiply/produce an infection) in exposed host
 It can be studied/measured using
 The speed with which an infectious agent spreads with in a
population of close contacts /secondary attack rate
 SAR = (# new cases in a group – initial cases)
(# of susceptible persons in group – initial cases)
 Sero-surveys after epidemics to determine the proportion of
persons recently infected.
 Measuring the progression of an infectious agent from
exposure to infection (infection rate)
 Infection rate (IR) = total number of infected people x 100
Total no
susceptible people
 Host and environmental factor as well as dose route of entry,
source of infection, strain of agent influence the infectivity of
an agent.
69BY GN 2013

70. 2.Pathogenicity
Ability of an agent to produce clinically
manifest disease in susceptible host.
Measured by the proportion of infections that
result in clinically apparent disease
Laboratory methods also help full
Pathogenicity = total number of clinical cases x 100
Total number of sub-clinical case
70BY GN 2013

71. Virulence
Ability of an agent to produce severs disease.
Measured by proportion of clinical cases
resulting in sever clinical manifestation
including squealed
Measure of virulence for human
Case fatality rate (CFR)
 Hospitalization rate
Proportion of cases disabled or who have
developed Squeal
Proportion of cases that require different kinds of
treatment
71BY GN 2013

72. Virulence cont’d
Note
High infectivity different from High Pathogenicity
High Pathogenicity different from High virulence
e.g.
Rhinovirus infection: High Pathogenicity but low virulence
Measles infection :high Pathogenicity low
virulence
HIV: High Pathogenicity & high virulence
72BY GN 2013

73. Factor determine the degree of infectivity,
Pathogenicity and virulence
Strain of the agent e.g. N- Meningitides
Dose of the agent e.g. Cholera
Route of infection
Treatment especially on virulence
Season
Host factor
Age
Nutritional status
Immune response
73BY GN 2013

74. 4.Antigencity
Ability of the infectious agent to induce
immune response and thus an immune state
in the host.
5. Toxignocity
Refers the ability of agent to produce toxin or
Poison
6. Resistance
Ability of the agent to resist adverse
environmental condition during transmission
from one host to another
74BY GN 2013

75. 7. Disease Prevalence Rate
Number of current cases per population at risk
Old: Persistent active disease contracted previously
New: Onset of active disease
# of EXISTING cases of a specified disease
 Point prevalence
Prevalence at a specific point in time
Period prevalence
Prevalence over a given time interval
Usage
Measure amount of illness in the community
Determine health care needs of the community
75BY GN 2013

76. 8. Disease Incidence Rate
Number of new disease cases per population at
risk
¨ High incidence implies high disease occurrence
¨ Low incidence implies low disease occurrence
¨ # Of NEW cases of a disease in a period of time
¨ Population at risk of developing the disease during
the same period of time
Measured over a given time interval
Usage
Determine probability of developing a specific disease
Used to detect etiologic factors
76BY GN 2013

77. 9: Immunogenicity
Infection’s ability to produce specific immunity in
the host e.g. measles
Measured by serologic surveys
Depends on:
Amount of antigen formed in the host
Site of multiplication
Agent’s ability to induce lifelong immunity
77BY GN 2013

78. Diseases According to Host-related properties
78BY GN 2013

79. unit five
Source of infection
Learning objectives
1.Explain the three main sources of infection
79BY GN 2013

80. Source of infection
There are three main sources of infection
1.Humans
2.Environment (inanimate, including food &
water)
3.Other animals
80BY GN 2013

81. A) Humans
People are colonized by a wide variety of microorganisms
most of which can become pathogenic given the right
conditions.
Normal body flora of the healthy individual vary from one
person to another depending on age, general health,
temperature and specific local condition such as acidity in
the stomach.
If normal conditions are altered, then the normal flora
may be destroyed and replaced by harmful organisms .
Any individual can be a source of infection although it is
traditional to call exogenous infection
81BY GN 2013

82. B) The inanimate environment
Soil, food and water can harbor organisms
which act as a source of injection under the
right conditions.
For example, soil can contain clostridium
species and if a traumatic penetrating injury
carries these organisms deep into tissue
anaerobic conditions may permit the organism
to multiply.
82BY GN 2013

83. C) Other animals
A variety of diseases can be spread from
animal to man and these are called zoonosis
Zoonosis is an infectious disease of animals
that may be transmitted to man.
Example Brucellosis, Rabies, Toxoplasmosis
83BY GN 2013

84. Unit six
Carriers and Infected individuals
Learning objective
1.Explain the four types of carries
84BY GN 2013

85. Carries
A person or animal that does not have apparent
clinical disease but is potential source of
infection to other people
85BY GN 2013

86. Type of carriers and its role
1.Incubatory carrier or precocious carrier (but not all
disease)
Transmitting disease during incubation period i.e. from the
time of 1st
shading to manifestation.
E.g. Mumps ,measles
2.Convalescent carrier
Transmit infection during recovery i.e. from time of recovery
to when agent stops shading
E.g. Typhoid fever ,Diphtheria
3. Asymptomatic carrier (Healthy)
Transmitting a disease without ever showing clinical
manifestation
High carrier rate e.g. Polio, Ameobiasis, meningo coccus
4.Chronic carrier
Transmitting disease for long period/ indefinite transmission
E.g. Viral Hepatitis (B, c) , Typhoid fever
86BY GN 2013

87. Unit seven
Course of an infectious disease over time
Learning objective
1.Discuss courses of an infectious disease over
time
87BY GN 2013

88. Prepatent period
¨ The time interval between infection and the point at which
infection 1st
detected(lab method).
¨ Between biological onset and the time of first shading of the
agent
¨ Measured by the 1st
shading of infectious agent by host.
2.Incubation period
Time interval between infection and the 1st
appearance
of clinical manifestation of disease i.e. between
biological and clinical on set.
Used in investigation of disease out break
88BY GN 2013

89. 3.Communicable period
The period during which an infected host can
transmit the infection to other
Measured by the length of time in which the
agent shades by host.
Degree of transmissibility does not remain
constant throughout the period of
communicability as the amount of the agent
that shade by infected host is variable at
different point in time.
89BY GN 2013

90. 4 Generation time
Onset of infection to maximal communicability
of the host (during or after incubation period)
It applies to both apparent and unapparent
infection
Focuses on transmission of infection as core
concept.
90BY GN 2013

91. 5.Latent period
The time interval between recovery and the
reoccurrence (as a relapse)
6.Prodormal period
From onset of symptom to appearance of
characteristic manifestation
91BY GN 2013

92. Unit eight
Spectrum of infectious disease/ gradient of infection/
Learning objective
1.Mention the possible outcome of infectious
disease
92BY GN 2013

93. Spectrum of infectious disease/ gradient of infection/
Spectrum means range of possible option for
something
Spectrum of infection implies the range in the
expression of disease be it in terms of the degree of
severity or clinical manifestation.
The Sequence of event takes place in the host
depending on the variety of host response.
The sequence of event may be
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94. Spectrum of infectious disease cont’d
Five type of reaction in spectrum of disease
1. No Reaction  No infection
2. Sub clinical or unapparent infection
3. Atypical disease
4. Frank disease
5. Sever disease
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95. Unit nine
Natural history of disease
Learning objective
1.Define natural history of diseases
2.Explain the four stages of natural history of
diseases
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96. Natural history of disease
Definition
• A course of disease over time in the absence
of any intervention or unaffected by
treatment.
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97. Natural history cont’d
Characteristics
Each disease has its own natural history
Intervention or treatment modifies the course of
disease through time
Helps to understand the intervention measures that
could be under taken in order to prevent or control
diseases.
Has four stages
1. Stage of susceptibility
2. Stage of pre-symptomatic disease
3. Clinical stage
4. Stage of disability
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98. Natural history cont’d
Stage of susceptibility
Period of exposure
Disease has not yet developed but there are
factors that favour occurrence (risk factors)
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99. Natural history cont’d
Stage of pre-symptomatic disease – sub clinical
stage
Period of latency
Period biological onset
Disease process has already began but no s/s are
detectable
Initiation of disease process can be evidenced by
investigation methods (lab investigation)
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100. Natural history cont’d
Clinical stage
Sufficient and organ change occur
Sign and symptoms of disease appears
Severity of a disease is variable depending on the
interaction certain factor such as
¨ Nutritional status
¨ Immunity of individuals
¨ Virulence of the agent
¨ Presence or absence of medication
¨ Presence of underlying illness
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101. Natural history cont’d
Stage of disability or death (outcome)
¨ Disease has occurred and left over damage to
the body
¨ residual long or short duration disability
¨ chronicity
¨ death
¨ Note – Recovery can take place at any stage
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102. Unit ten
Epidemiology and general methods of
prevention and control of communicable
diseases
102BY GN 2013

103. Introduction to epidemiology of
communicable disease
Definition:
 Epidemiology is the study of the frequency,
distribution and determinants of diseases and
other health related events in specified
populations
the application of this study to the promotion
of health and to the prevention and control of
health problems (Last 1983).
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104. Components of the definition
Population
The focus of epidemiology is mainly on the
population rather than individuals.
Frequency
Shows epidemiology to be mainly a quantitative
science
It is measured by morbidity rates which quantify the
occurrence of illness
Mortality rates which quantity the occurrence of
death
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105. Health related conditions
conditions with directly or indirectly affect or
influence health
Distribution
Refers to the geographical distribution of
diseases, the distribution in time, or / and
distribution by type of persons affected.
The part of epidemiology concerned with the
frequency and distribution of diseases by time,
person and place is named descriptive
epidemiology.
It asks the questions: - How many? Where?
When? What?
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106. Determinants
Are factors which determine whether or not a
person will get a disease, or in other words,
the causative factors for disease
The part of epidemiology dealing with the
causes and determinants of diseases is
analytical epidemiology
It asks the questions. How? Why?
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107. Importance of Studying Communicable Diseases
Epidemiology
Offers insights in to why disease and injury afflict some
people more than others
why they occur more frequently in some locations and
times than in others
applied science with direct and practical applications
For most effective ways to prevent and treat health
problems.
Discovery of new infections
The possibility that some chronic diseases have an
infective origin.
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108. General methods of prevention
and
control of communicable diseases
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109. Disease prevention
Inhibiting the development of a disease
before it occurs or if it occurs interrupting or
slowing down the progression of diseases.
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110. Disease control
Involves all the measures designed to reduce
or prevent the incidence, prevalence and
consequence of a disease to a level where it
cannot be a major public health problem.
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111. Levels of disease prevention
The different points in the progression of a
disease at which one can intervene to prevent
further out come.
There are three levels of prevention.
¨ Primary
¨ Secondary
¨ Tertiary
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112. Primary prevention
Preventing health people before becoming sick
by altering susceptibility or reducing exposure for
susceptible individuals
In order to carry out effective p° prevention
know first who is most “at risk” of getting
disease.
Purpose (Objective)
Promotion of health
Reducing incidence of disease
Prevention of exposure
Prevention of disease
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113. Health promotion
Consists of general non specific Interventions
those enhance health.
Aim at individual, communities, organizations
and Policies
Promotion measures include
¨ Improve socio economic status of the population
¨ Good nutrition, clothing, shelters, rest
¨ A void risk behaviour
¨ Broad area of health education
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114. Prevention of exposure
Any intervention which prevents the coming
in contact between an infectious agent and a
susceptible host.
This includes actions such as
Provision of safe and adequate water
proper excreta disposal
vector control
safe environment at home, at school and at work
on the streets
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115. Prevention of disease
During the latency period between exposure
and the biological onset of the disease.
 An example for this is immunization.
N.B. Immunization against an infectious
organism does not prevent it from invading
the immunized host but prevents it from
establishing an infection.
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116. Prevention of disease cont’d
Breast feeding is an example of intervention that
acts at all three levels of primary Prevention.
Health promotion: By providing optimal nutrition for a
young child, either as the sole diet up to six months of
age, or as a supplement in later age.
Prevention of exposure: by reducing exposure of the
child to contaminated water.
Prevention of disease after exposure: by the provision
of ant-infective factors, including antibodies, WBCs
and others
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117. Primary prevention cont’d
Target- total population
Specific protective measures
Immunization
Environmental sanitation
Prevention against accidents
Prevention of occupational hazards
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118. Secondary prevention
(2°preventions)
Prevention after biological onset but before permanent
damage occur
Include early dictation and prompt treatment of disease in
such a way that it is possible to:
¨ Cure disease (curative medicine)
¨ Slow the progression
¨ Prevent complication
¨ Limit disability
¨ Reverse communicability
¨ Reduce prevalence.
On community-Secondary prevention for the infected
individual and p° for potential contacts
Target population→ patients (clinical or sub clinical)
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119. Tertiary prevention
Takes place after permanent damage
Important aspect of therapeutic and
rehabilitation medicine
Aim at treatment to prevent disability and
death
¨ New training and especial education to help the
patient to return to some useful work & life in
community.
Target- patient: E.g. Physiotherapy
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120. Principles of communicable disease control
Elimination of Reservoir
Immunization
Environmental control
Vector control
Surveillance
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121. Elimination of Reservoir
Man as reservoir
Detection and adequate treatment
Isolation
Quarantine
Animal as reservoir
¨ Action will be determined by usefulness of the
animal
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122. Immunization or vaccinations
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Introductions
The new born may carries antibodies transmitted
from its mother across the placenta and from
early breast feeding which protecting at very
vulnerable stage in life
The effect of this antibody wears off after six
weeks to six month thereby the child makes their
own from natural or artificial infections
(immunizations)

123. Immunization cont’d: Definitions of
important terms
BY GN 2013 123
Vaccination: Administrations of any vaccine
or toxoids
Immunization:
The process of inducing immunity artificially
by administering antigenic substance
There are two types of immunizations;
active immunization and passive
immunization

124. Immunization cont’d: Definitions of
important terms
BY GN 2013 124
Active immunization: Involves the stimulation of
immune system to produce antibodies and
cellular immune responses that protect against
infections. Example use of vaccine agents
Passive immunization: the process of producing
temporary protection through administration of
exogenously produced anti body such as
Immunoglobulin. Example breast milk

125. Immunization cont’d: Definitions of
important terms
BY GN 2013 125
Toxoids: Modified bacterial toxin that has been made
non toxic but retain the capacity to simulate antitoxins
Immunoglobulin: an antibody containing solutions
made available for passive immunizations
Antitoxin: an antibody derived from the serum of
animals from stimulations with specific antigens which
used to provide passive immunity

126. Immunization cont’d: Definitions of
important terms
BY GN 2013 126
Vaccine: a suspension of attenuated life or killed
micro-organisms or antigenic portions of these
agents presented to potential hosts to induce
immunity and prevent disease. Vaccine can be life
attenuated, killed organisms and toxoids
Life attenuated; giving actual infection which is the
best of all; examples measles, polio, BCG
Killed organisms: used when live attenuated strain is
impossible to produce; it should be repeated.
example pertussis

127. EPI target disease in Ethiopia
BY GN 2013 127
Before 2007
øTuberculosis
øTetanus
øPertussis
øDiphtheria
øMeasles
øPoliomyelitis
After 2007
«Tuberculosis
«Tetanus
«Pertussis
«Diphtheria
«Measles
«Poliomyelitis
«Hepatitis B
«Haemophilus influenzae B
« Pneumonia
«Rota virus

128. Antigen for immunization
BY GN 2013 128
1. BCG
2. Penta-valent (DPT plus HiB&Hb)
3. Polio
4. Measles
5. Tetanus toxoids( TT)
6. PCV
7. Rota virus

129. Epidemiological case definitions of vaccine
preventable disease
BY GN 2013 129
Measles: any child with fever, red eyes, and generalized
rash within three or more days and history of cough,
runny nose.
Pertusis: any child with history persistent cough for two
or more weeks, fits, and cough followed by vomiting
Neonatal tetanus: Neonate with history of normal suck
and cry in 1st
two days of life and onset of illness between
3-28 days of age with inability to suck breast followed by
stuffiness and/or convulsions more often death
Poliomyelitis: any child less than 15 years and who have
AFP or any child who clinical suspect polio

130. EPI delivery strategy
BY GN 2013 130
Static: immunization performed as a part of
routine activities of the health institution
Outreach: is an immunization approach in which
the staff of the health unit goes out and
administers vaccine for mother and children
Mobile: a team of health unit staff go out of the
health institutions and provide immunization as
Mopping up or house to house mainly for single
dose antigens
campaign: like as national immunization days

131. Environmental control
¨ Personal and domestic hygiene
¨ Proper preparation, handling ,cooking and
storage of food
¨ Use of safe water source
¨ Proper disposal of wastes and excreta
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132. Vector control
¨ Adulticids
¨ Repellents or detergents
¨ Personal protection
¨ Larvicide’s
¨ Biological control
¨ Environmental modification
¨ Insecticides
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133. Adulticids
Killing of adult mosquito can be done while:
¨ Flying – using knock down spray
¨ Resting- Residual insecticides
Repellents or detergents
Applied on the body in the form of lotion or
smocks
Do not kill but deter from biting
Made from phyethroids but other insecticide can
be added
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134. Personal protection
Reduce the no of mosquito bite
They are cloths that cover the arms and legs
Can be combined with repellents
Mosquito nets
Larvicide’s
Act on mosquito larva by acting on
Breathing apparatus
Not effective
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135. Biological control
Use of natural methods to bring about
reduction in vector
Environmental modification
Making the environment no longer suitable
for existence of the vector
E.g. draining of water
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136. Insecticides
Poisons – Paris green
Fumigants
Hydrogen cyanides, methyl bromide and ethylformate
 used on body or clothing to destroy infestation
Knock down – Pyrethrum
Residual insecticide
Organo chlorines
dichlorodiphenyltrichloroethane (DDT)
Benzenehexahloride (RHC) - Dieldrin
kill or reduce time of contact
Organophosphate e.g. Malathion
inhibits cholinesterase at nerve junction and cause paralysis
143BY GN 2013

137. Unit eleven
Surveillance and investigation and
management of outbreaks
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138. Surveillance
Surveillance is a continuous collection, analysis,
interpretation and dissemination of health information
for the purpose of monitoring health events, and using
the information for prevention and control of health
problems.
Key qualities (elements) of surveillance
Its continuous activity
Its ability to detect changes in ecology or incidence of
disease.
The dissemination of pertinent information for action.
Although surveillance is applicable to all types of
diseases, primary attention should be directed towards
disease amenable to effective control
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139. Methods of surveillance system
1.Active surveillance
2. Passive surveillance
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140. Active surveillance
A collection of data usually on specific disease or
health related events for relatively limited period
of time by regular outreach on the part of health
department personnel.
A system in health staff make periodic field visits
to health care facilities to identify new cases or
death from disease (case finding)
Involves
Interviewing clinicians and pts
Reviewing health records
Surveying villages in under developed countries
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141. Characteristics of Active surveillance
¨ Identify Local outbreak
¨ More expensive to maintain and establish as it
require good organization, funds and
resources.
¨ More accurate and complete than passive
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142. Passive surveillance
• Surveillance in which either available data on
reportable disease are used or reporting is
mandated or requested with the responsibility
often failing on health care provider or district
health officer.
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143. Characteristics of Passive surveillance
¨ Problems with under reporting or lack of
completeness
¨ May dilute small out breaks in the total
regional pupation
¨ In expensive and easily implemented
¨ Allow for international comparison
¨ Data is analyzed centrally
¨ Wide coverage requiring without specific
arrangement
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144. Types of passive surveillance
Total passive
 carried out through predetermined reports
 submitted at regular intervals
Simulated passive surveillance
¨ surveillance team request reports from third
parties
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145. Step to be followed in surveillance
1.Collection of data
Name, age, sex address, occupation, vaccination,
Treatment, place of infection, source of infection,
exposed susceptible e
1.Compilation and analysis of data
analysis can be made of cases by person, place and
time.
1.Formulation of recommendation for action
2.dissemination and feed back
 higher authorities
 Person and institution involved in notification &
control program
 To the community.
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146. Out break
Occurrences of more cases of disease than
expected in a given area among specific group
of people over particular period of time.
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147. Outbreak is:
A public, political and economic emergency
An unusual event
An event requiring rapid action
A failure of surveillance
An opportunity /for training, Research…)
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148. Reason to investigate out break
Control /prevention
Research opportunity
Training
Public political and legal concern
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149. Steps in outbreak investigation
1.Preparation for field work
A. Investigation
Have appropriate scientific knowledge, supplies
and equipment to carry out investigation
Discuss with someone who is knowledgably about
the disease.
Review applicable literature.
B. Administration
C. Consultation
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150. 2. Establish the existence of our break
3. Varity the diagnosis
4. Establish case definition
Include clinical criteria and restriction by time
place and person.
must be applied to all without bias
 Type
Possible – Fewer of typical clinical features
Probable – Typical clinical feature without lab
investigation.
Confirmed
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151. 5. Perform descriptive epidemiology.
Time- when do they become ill?
Place- where do they live
Person- who are the cases
5Develop hypothesis
source of the agent, made of transmission etc
Who is becoming ill?
What is a disease
What is the source and the vehicle
What is the mode of transmission
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152. 6. Test hypothesis
Compare with established facts When clinical,
lab environmental and/or epidemiological
data undoubtedly support hypothesis
8. Refine hypothesis and do additional studies
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153. 9. Implement control measures
Control source of pathogen
Interrupt transmission (vector contrle
,personal & environmental sanitation)
Modify host response :
Vaccination
Prophylaxis
Treatment
10. Communicate the findings
160BY GN 2013

154. Learning objective
1.List at least four diseases under national
regulation
2. list diseases under international regulation
161
Unit twelve
Notification and health regulation
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155. Introduction to Notification and health regulation
International health regulations Require that
certain disease are notified
Purpose
To warn other countries and intended travellers to
the country of health risk involved For assistance
Disease under international health regulation
¨ Plaque, cholera, yellow fever, Ebola
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156. Disease under surveillance by WHO
Louse borne typhus fever
RF
Paralytic poliomyelitis
Malaria
Influenza
AIDS
Small pox
Diphtheria, typhoid whooping cough
163BY GN 2013

157. National health regulation
TBC
Leprosy
Sleeping sickness
Vaccination required for international travel
 yellow fever
164BY GN 2013

158. Integrated disease surveillance and response
Functional disease surveillance system is
useful for priority setting, planning
mobilization and allocation of resources,
production and early detection of epidemics,
monitoring and evaluation of intervention
programs.
165BY GN 2013

159. Integrated disease surveillance and response
(IDSR) priority disease
1.Epidemic prone
 Cholera
 Diarrhoea with b/d (shigella)
 Measles
 Meningitis
Malaria
plague
 Viral Hemorrhagic Fevers(Ebola)
Typhoid fever
 RF
 Epidemic typhus
166BY GN 2013

160. 2. Disease selected for case based surveillance
Measles
Poliomyelitis
Dracunculiasis (Guinea worm)
Neonatal tetanus
3 .Other diseases of public health importance
Diarrhoea in <5 years of age
Pneumonia
AIDS
Onchocerciasis
STI
TB
167BY GN 2013

161. 168BY GN 2013