Concept on disease from public health view.pptx

he104;health science
[content2,class2]
by: rafia Rahman
Asst.prof,IHE-du

concept of disease 1. Definition of disease
2. Disease cycle
3. Spectrum of disease
4. Disease causation theories
5. Health problem of Bangladesh
6. International classification of
disease
Objectives;
i. To understand disease from public
health perspective.
ii. To conceptualized regard theories
of disease causation.
crosspondance; rafia643645@gmail.com 2

Definition of disease
 The term disease literally means “without ease”
(uneasiness), when something is wrong with bodily function.
 The simplest definition is that disease is just the opposite of
health: i.e. any deviation from normal functioning or state of
complete physical or mental well-being.
 Webster defines disease as “a condition in which body health is
impaired, a departure from a state of health, an alteration of the
human body interrupting the performance of vital functions”.
 The oxford English Dictionary defines disease as “ a condition of
the body or some part or organ of the body in which its functions
are disturbed or deranged”.
 Ecological point of view disease is defined as “a maladjustment of
the human organism to the environment.”

Distinction between Disease, Illness and Sickness
Disease is a physiological/psychological dysfunction.
Illness is a subjective state of the person who feels aware of not being well. Illness refers to the
presence of a specific disease, and also to the individual’s perceptions and behavior in response to
the disease, as well as the impact of that disease on the psychosocial environment.
Ill-health losses individual utility and social welfare in many ways both directly and indirectly by
reducing the enjoyment or utility associated with the consumption of goods and services unrelated to
health, or by compromising other economic objectives.
Sickness is a state of social dysfunction i.e. a role that the individual assumes when ill (sickness
role).

Disease Cycle
Definition; Disease cycle explain the stages through which most of the diseases passes
during their natural course. Disease may be communicable or non-communicable and others
indirect facts like burn, accident and natural disasters that responsible to fluctuate health
status.
Stage; six stages –
1. Incubation period for stage1
2. Prodromal period or stage2
3. Typical clinical period/Fastigium or stage3
4. Defervescence or stage4
5. Convalescence or stage5
6. defection or stage6
Incubation
Fastigium
Differvescence
Convales-Scence
Defection
Differential
Point
Point of Invasion
Prodromal Symptoms:
Nasal discharge,
headache mild
fever,general aching,
irritability,
restlessness,digestive
disturbances, cough
Fig- Disease cycle
Prodromal Point

Cont…………….
Incubation period is the time interval between the entry of causative agent in the body and
manifestation of the clinical signs and symptoms.
The range of the time is varies from a few hours to few days, sometimes takes 10 days to 3 weeks
and for a few disease like AIDs incubation period for long time about years.
Prodromal stage is a short period ranging from 1 to 4 days
characterized by period of vague signs and symptoms (such as headache, nausea, fever, body
ache,ect) are manifested. Clinical diagnosis is usually not possible due to vagueness of the sign
and symptoms.
Fastigium period is typical clinical period, the patient become ill and sign, symptoms of specific
disease are clear-cut and push patient to bed. Diagnosis of the disease is possible in this stage.

Cont…………..
Defervescence stage the clinical symptom indicate the pathogenesis process is going on in the
body, continuous physio-biological changes is impelling. After that body's defensive mechanism
begins to take an upper hand over the pathogens and patient begins to feel better it called
defervescence stage.
Convalescence stage either for body defense mechanism that is body immunity or for medicine
or for both the patient is recovery from disease but may still harbor the disease agent called
convalescence stage.
Last stage is defection, during this stage the individual recover fully from the disease but in some
cases may continue to harbor the disease agent for a varying period.

Cont………..
Significance of disease cycle
 Disease cycle tell the communicability period of the
disease agent.
 The time during which infectious agent transferred
from one infected person to another healthy person
or from One infected person to susceptible host
person or from infected person to another infected
person.
 Some diseases are more communicable during the
incubation period than during actual illness.
 Diagnosis and treatment may reduce period of
communicability and virulence in some extend.
one infected person to
another healthy person
from One infected
person to susceptible
host person
• OR
from infected person
to another infected
person.
• or
Fig. Transfer of infectious agent

Spectrum of Disease
Definition- The spectrum of disease is a graphic
graphical representation of variations in the
manifestation of disease.
Health and disease spectrum shows fluctuation of health to
fatal stage of life.
Characteristics/what explain
 At the one end of the disease spectrum is subclinical
infections that usually not identified and other end is
fatal illness.
 The middle of spectrum represent illness ranging in
severity from mild to severe.
 These different manifestations are actually reflections of
individual’s different states of immunity and receptivity.
Health Subclinical
Infection
Clinical illnesses (mild, moderate, severe) Fatal Illness Disease
Disease spectrum

Cont………
 The Spectrum of Health also well known as Health Sickness Spectrum,
 Fluctuation of the health condition from maximum healthy (functioning)
state to death of a person.
 The health spectrum have various levels of fluctuation, started from
function state to total dysfunction.
 The sickness spectrum state, the health of an individual is not static it
is dynamic phenomenon and a process of continuous change.
 The highest point is positive health the others levels of dysfunction and
the lowest point of the spectrum is death.
Positive health
Health
Mild Subclinical infection
Moderate subclinical infection
Severe Infection
Fatal illness
Fig. Health Disease Spectrum

Grasp ’spectrum of disease” covid19

Disease causation; Introduction
Disease causation:
Any event or condition, characteristics or combination of these factor which
plays an important role in producing the disease cause may not be a single
factor and often comprises several components.
For e.g., in case of food poisoning due to Salmonella. The presence
of Salmonella is necessary cause. Contaminated food (salad) is the sufficient
cause. Necessary cause is the component of sufficient cause.
Factors involved in disease causation: Four types of factors that play
important role in disease causation.
1. Predisposing factor may create a state of susceptibility of disease to host.
E.g., age, sex, previous illness.
2. Enabling factor favors the development of disease. E.g., poor housing, poor
sanitation, poor nutrition, low economy.
3. Precipitating factor is most important for disease causation. It is associated
with onset of disease. E.g., exposure to specific infectious agents or toxins.
4. Re-enforcing factor may aggravate and establish disease. E.g, repeated
exposure, hard work.
“BEINGS” Model of Disease Causation
complex interplay of nine different factors
b Biological factors (innate)
b Behavioral factors (individual lifestyles)
e Environmental factors
i Immunological factors
n Nutritional factors
g Genetic factors
s Social factors
s Spiritual factors
s Services factors (health care services)

CONCEPT OF CAUSATION
Definition of “cause” ; Any event, act or condition preceding disease or Illness without which
disease would not have occurred or would have occurred at a later time.
Disease cause from;
 a complex interaction between man, an agent (or cause of disease) and the environment,
 infectious organism (germ) may responsible for disease, agent → Man → Disease
 multiple factor can involve for develop a disease and multiple approaches needs for the
prevention/control of disease.
 the predisposing factors of any type and their complex interrelationship with each other.
 distinguish stage or phage needs to develop a disease, to develop disease needs to go
through a process and complete the process

Disease causation theories
Disease causation theories are;
1. Supernatural Theories& karma
2. Hippocratic Theory/ Theory of
humors (humor means fluid)
3. Theory of Contagion
4. Miasma Theory
5. Theory of spontaneous generation
6. Germ Theory (Koch postulates)
7. Epidemiologic Theory
8. Multifactorial causation
9. Webs of Causation
10. Theory of general susceptibility
Supernatural& karma
Disease causation theories
Old theories Modern theories
Theory of humors
Miasmatic Theory
Theory of Contagion
Germ Theory
Multifactorial causation
Epidemiologic Theory
Webs of Causation
T/O spontaneous generation
A pattern of response by a living organism to some form of invasion by a foreign substance or injury
which causes an alteration of the organisms normal functioning.
An abnormal state in which the body is not capable of responding to or carrying on its normally
required physiological functions accordingly.

Supernatural theory of disease
Definition; n the early past, the disease was thought mainly due to either the
curse of god or due to the evil force of the demons. People used to please the
gods by prayers and offerings or used to resort to witchcraft to tame the
devils.
It was believed that “disease is due to super power” (e.g. gods, evil spirits), a
result of activity of an individual (karma).
Attributed to a variety of spiritual or mechanical forces, including:
 A punishment from God for a sinful behavior.
 Weak moral character.
 Witchcraft.
Presently, 10% in developed and 30% in developing countries still believe in
supernatural origin of disease
Problem/difficulties is “Today superstitions are becoming a major obstacle to
disease control”.

Theory of Humor [ Hippocrates 430-330 B.C. ]
Hippocrates promoted the concept that disease was the result of
an imbalance among four vital "humors" within us: Yellow Bile,
Black Bile, Phlegm and Blood.
• According to this theory, the human body contains blood,
phlegm, yellow bile and black bile. These are the things that
make up its constitution..
• Health is primarily that state in which these constituent
substances are in the correct proportion to each other, both in
strength and quantity, and are well mixed.

Cont….
 Hippocrates believed that if one of the humors became
excessive or deficient, health would deteriorate and
symptoms would develop.
 Hippocrates was a keen observer and tried to relate an
individual's exposures (e.g., diet, exercise, occupation,
and other behaviors) to subsequent health outcomes.
 Consequently, his recommendations and
"prescriptions" were often based on his observations
and his perception of cause and effect.
 His disease model, however crude, also suggested
seemingly logical interventions. For example, if he
surmised that an individual suffered from too much of
the humor "blood", he prescribed blood letting to
alleviate the problem.

Theory of Contagion (Fracastoro) 1546
• Contagion is a corruption which develops in the substance of a combination, passes from
one thing to another and is originally caused by infection of the imperceptible particles.
• He called the particles Seminaria (seeds).
• Differences between diseases are explained by they’re having different “active particles”
different seeds.
• He did not abandon the humoral theory he blended it with his contagion theory suggesting
that seeds for different diseases have different affinities for different humors.
• Treatment : destroy or expel the seeds of contagion
1)Destroy : extreme heat and cold.
2)Expel : bowel movements, urination, sweating and blood-letting.

Theory of Contagion
Specific contagious material not
identified BUT knowledge that
Disease can spread from person to
person as early as 15th century
Each disease related to a different
contagion
Contagions in humans & environment
Contagion + Environmental:
• Both attributed disease to
external force
• Both led preventative measures
E.g. Italy – sanitation to control
TB and plague by quarantine on
ships

Theory of Miasma
 Miasma - bad or malodorous air as a
cause of disease
 Pleasant or strong smelling agents were
thought to be protective
 Public health efforts concentrated on
finding the source of bad smells

Cont…
 The word "miasma“ comes from Ancient Greek and means
"pollution"
 Considered to be a poisonous vapor or mist filled with particle
from decomposed matter (miasmata) that caused illnesses.
 In the 1850s miasma was used to explain the spread of cholera
in London and Paris
 In China miasma was thought to be caused by the heat,
moisture and the dead air in the Southern Chinese mountains.
They thought that insects waste pollute the air, water.
 This theory was consistent with observation that disease was
associated with poor sanitation.
Result of miasma;
The sanitary movement era, first half of
1900s;
i. Public health measure were
concerned with sanitation
ii. Focus was on disease prevention
(causes of diseases in population)
and the health needs of poor
population.
iii. The epidemiology were largely
involved in population-wide health
improvement

The theory of spontaneous generation (abiogenesis)
 This theory proposes that living organisms can arise from nonliving matter.
 It was proposed by Aristotle (384–322 BC) and was widely accepted for almost 2000 years, until flies-
infested meat experiments by Francesco Redi (1626–1697) challenged it.
 In the 18th century, British scientist John T. Needham (1713–1781) conducted boiling beef gravy and plant
infusion experiments in air-tight vials suggesting that ‘life force’ causes inanimate matter to come to life
and perhaps spontaneous generation of microscopic life was indeed possible, but in 1799, experiments by
Italian scientist Lazzaro Spallanzani (1729–1799) reported results that contradicted Needham’s findings.
 The debate continued until experiments by French scientist Louis Pasteur (1822–1895) using swan-necked
flasks that remained free of microbes disproved the theory definitively.
 The English physicist John Tyndall dealt a final blow to spontaneous generation in 1877 by demonstrating
that dust did indeed carry germs and that if dust was absent browth remained sterile even if directly
exposed to air.

Cont……
Contribution of theory of abiogenesis to microbiology ;
The debate over spontaneous generation led in part to the
development of a generalized scientific method by which
questions are answered through observations of the outcomes
of carefully controlled experiments.
It consists of four steps:
1. A group of observations leads a scientist to ask a question
about some phenomenon.
2. The scientist generates a hypothesis—a potential answer to
the question.
3. The scientist designs and conducts an experiment to test
the hypothesis.
4. Based on the observed results of the experiment, the
scientist either accepts, rejects, or modifies the hypothesis.
It also contributed to the ‘Golden Age Of Microbiology”

Germ Theory of disease
Germ theory defines that the invasion of microorganisms such as bacteria, viruses, fungi, or protists
in our body causes certain types of diseases. It was believed that each disease has a single and a
specific cause (mono-causal approach).
Characteristics;
 These microorganisms are too small to be seen with our naked eye and require a magnifying
microscope for better visualization.
 They grow and reproduce within the host body and cause infectious diseases.
 Not only pathogenic organisms cause severe disease but also environmental, genetic factors, and
potential host influence the severity of the disease.
 The theory generally referred to as one-to- one relationship between disease agent and disease.
• Health problems were believed to be the product of living organisms which entered the body
through food, water, air or the bites of insects or animals.

Cont………..
So, The germ theory of the disease is generally
referred as a one to one relationship between the
causal agent and disease.
Koch’s Postulates in germ theory the organism
must be present in every case of the disease; the
organism must be able to be isolated and grown in
pure culture; the organism must, when inoculated
into a susceptible animal, cause the specific
disease; the organism must then be recovered
from the animal and identified.

Cont………..
Result of theory/contribution;
1. Researches were moved from the community to the laboratory and concentrated on
the identification of agents for a given disease.
2. Medical practice became devoted to the destruction or eradication of the agent from
individuals already affected
The criticism has also appeared to oppose this theory. It is now found that a disease is
rarely caused by a single agent alone, but rather depends upon a number of factors which
contributes to its occurrence.

Epidemiological triad/ triangle
 According to this theory, exposure to an agent does not
necessarily lead to disease. It was believed that disease
is the result of an interaction between agent, host and
the environment.
 It was believed that diseases can be prevented by
modifying factors which influence exposure and
susceptibility.
 Epidemiologic triad concept of disease causation
involves the role of 3 factors- agent, host and
environment for the appearance of disease.

Cont….
 Thus, the 3 factors which refer as the causative
factors of disease are called epidemiological triad.
Significance/Contribution;
 This model helps epidemiologists to focus on different
classes of factors especially with regards to infectious
diseases.
 This model clears that “the mere presence of agent,
host and favorable environmental factors in the pre-
pathogenesis period is not sufficient to start the
disease in man.
 What is required is an interaction among these
factors to initiate the disease process in man.”

Cont…..
Criticism/Limitation;
 useful in understanding infectious disorders better,
 less useful in dealing with chronic, degenerative diseases such as heart diseases and
diabetes.
Result of this; develop theories for chronic diseases
 Web of causation of disease
 Multifactorial causation of disease

Multifactorial Causation
 This theory was propounded by Pottenkofer of Munich.
 This theory describe that the disease is not caused by
single agent like in germ theory but many other factors.
 The use of chemotherapy, antibiotics and other drugs only
communicable diseases began to decline and replaced by
modern disease like lung cancer, coronary heart disease,
mental illness etc,
 These disease could not be explained on the basis of germ
theory of disease nor could they be prevented by
traditional method of isolation, immunization or
improvement of sanitation.

Cont…
 Multiple factor leads to the diseases common in non-
communicable diseases
 The germ theory of disease was overshadowed by multi-
factorial cause theory in 19th century.
 As a result of advancement in public health, communicable
diseases began to decline and are replaced by new type of
diseases so called modern disease of civilization.
Example: Lung cancer, CHD, Mental illness etc. The disease
could not be explained on the basis of germ theory of
disease and can not be controlled or prevented on that basis.
The realization began that multiple factors are responsible for
disease causation where there is no clear single agent.

Multifactorial Causation
 The idea of the single cause of the disease was oversimplification and there are other factors in
aetiology of diseases-social, economic, cultural genetic and psychological which are equally
important.
 For example, tuberculosis is not merely due to mycobacterium tuberculosis, other factors such
as poverty, overcrowding, smoking, malnutrition, contribute its occurrence.
 The purpose of knowing multiple factors of disease is to quantify and arrange them in priority
sequence for modification to prevent particular disease.

Web of causation
Suggested by MacMohan and Pugh in their book
“Epidemiologic Principle and Methods (85).
 According to this concept, disorders are developed through
complex interaction of many factors.
 These factors maybe biophysical, social or psychological
and may promote or inhibit the disease at more than one
point in the causal process.
 Ultimately, they determine the level of disease in a
community.
 The various factors (e.g. hypercholesterolemia, smoking,
hypertension) are like an interacting web of a spider.
 Each factor has its own relative importance in causing the
final departure from the state of health, as well as interacts
with others, modifying the effect of each other

Cont….
Significance/Contribution;
 Ideally suited in the study of chronic disease, where the agent is often not known and disease is the
outcome of interaction of multiple factors.
 This model of disease causation considers all predisposing factors of any type and their complex
interrelationship with each other.
 The web of causation does not imply that the disease can not be controlled unless all the multiple
causes or chain of causation or at least a number of them are appropriately controlled.
 Sometimes, removal of one link may be sufficient to control disease.
 Based on this theory, it is believed that prevention offers a better prospects for health than cure,
since many of these factors can be modified.
 Since several factors contributes to several diseases, community efforts were shifted to factors
modification (prevention) rather than disease treatment.

Theory of general susceptibility
 This theory is not concerned with
identifying single or multiple risk factors
associated with specific disorders.
 It seeks to understand why some social
groups seems to be more susceptible to
disease and death in general
 This reflects an imperfectly understood
general susceptibility to health problems.

Natural history of disease
Natural history of disease refers to the progress of a disease process in an individual
over time, in the absence of intervention. The process begins with exposure to or
accumulation of factors capable of causing disease.
Why it is important?
It is one of the major elements of descriptive epidemiology.
Understanding the progress of disease process and its pathogenetic chain of events
is must for the application of preventive measures.
Two major phage/stage; i. Pre-pathogenesis phase, ii. Pathogenesis phase
Deletion and treatment of any stage of disease can alter the natural history.

Natural history of disease
Co-interrupted pathway of disease. It refers to the description of
uninterrupted progression of disease in an individual from the
moment of exposure to causal agent until death, recovery or
disability.
It comprises various stages:
• Pre-pathogenesis phage: Interaction between agent, host
and environment.
• Pathogenesis phage: Entry of pathogen, incubation
period and appearance of sign and symptoms of
disease. This phage is called pathogenesis phage.
• Late pathogenesis phage: recovery, disability or death
• Prognosis: Prediction of the course of particular event of
disease that will occur in future.
Based on defined group of patients and can be done by clear
understanding of natural history of disease.

Health Problem of Bangladesh
In broad aspect major health problems in Bangladesh ;
1.Population problem
2.Communicable Diseases problem
3.Non communicable Diseases problem
4.Nutritional problem
5.Drug addiction/dependence problem among the high risk group
6.Road/ traffic accident and other accidents e.g. drowning
7.Medical care problem
8.Environmental health problem
9.Sanitation problem
10.Violence against women
11.Violence against men
12.Child abuse/ child labor
13.Unemployment problem
14.Food adulteration problem
15.Problem of Social violence (Anti-social activities, substance
abuse)
NB; Each have specific numbers of problems.
Health is constitutional (article3) right of each citizen of Bangladesh. Health problem means “the type of diseases people suffer
most, diseases lead to develop complication or worse the condition and the type of diseases people admit in hospital and die”.

Common cause of admission in all type of hospital
and number of death;
Children aged5,
Person aged between 30&70
Leading cause of death, WHO
Source; Health Bulletin 2016, DGHS,Bangladesh.

International Classification of Disease
World Health Organization (WHO) give three primary reference classifications-
1. International Statistical Classification of Diseases and Related Health Problems (ICD)
2. International Classification of Functioning, Disability and Health (ICF)
3. International Classification of Health Interventions (ICHI)
Here only the chart of international classification of disease incorporate to give a soft touch
only. This classification based on three priority issues, i. problem, ii, disability and iii.
Intervention.

Know……………

End of content,2
questions for common grasp

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