8/14/2019 Topic 1 - Theory & Principle of Disease
1/15
THEORY & PRINCIPLETHEORY & PRINCIPLE
OF DISEASE 1OF DISEASE 1
DISEASE CONTROL (DEMT 2433)
DIPLOMA IN ENVIRONMENTAL HEALTH
VICTORIA INTERNATIONAL COLLEGE
BY: MR KHAIRUL NIZAM MOHD ISA
DEPARTMENT OF ENVIRONMENTAL HEALTH
8/14/2019 Topic 1 - Theory & Principle of Disease
2/15
OBJECTIVESOBJECTIVES
Understand the definition of disease Understand the stages of diseases
Differentiate between epidemic and endemic
Explain basic concept of infectious diseases
Describe the causation of disease
8/14/2019 Topic 1 - Theory & Principle of Disease
3/15
INTRODUCTIONINTRODUCTION
Definition of Health:Health is a state of complete physical, mental and social well-being
and not merely the absence of disease or infirmity.
(WHO- World health Organization, 1948)
Definition of DiseaseA disordered or incorrectly functioning organ, part,
structure, or system of the body resulting from the effect of
genetic or developmental errors, infection, poisons,
nutritional deficiency or imbalance, toxicity, or unfavorable
environmental factors; illness; sickness; ailment.(dictionary.com, 2009)
8/14/2019 Topic 1 - Theory & Principle of Disease
4/15
Name of the diseases are based on: Appearance (eg. Erythema multiform)
Subjective sensation (eg. Headache)
Gross or microscopic appearance ( eg. Fracture of the femur or
adenocarcinoma of colon)
Causative factor (eg. Pneumococcal pneumonia)
8/14/2019 Topic 1 - Theory & Principle of Disease
5/15
STAGE OF DISEASESTAGE OF DISEASE
Stage of susceptibility Disease has not developed but the groundwork has been laid by
the presence of factors that favor its occurrence. Example, high serum cholesterol level increase the probability that
overt coronary heart disease will develop.
Risk factor (factors associated with an increased probability that
disease will develop later). Risk factor may be unchallengeable or
susceptible to change. Example, age, gender, race, family historywhich are not subject to change. Smoking, alcohol are changeable)
Stage of presymptomatic disease At this stage there is no manifest disease, but usually through the
interaction of factors pathogenic changes have started to occur. At this stage, the changes are essentially below the level of the
clinical horizon, the imaginary dividing line above which disease
manifest itself through detectable signs or symptoms.
Example, etherosclerotic changes in coronary vessels prior to any
signs or symptoms of illness (heart disease)
8/14/2019 Topic 1 - Theory & Principle of Disease
6/15
STAGE OF DISEASESTAGE OF DISEASE
Stage of clinical disease By this sufficient end-organ changes have occurred so that there
are recognizable signs or symptoms of disease.
Several classification depending on the specific disease.
Stage of disability Some disease resolve completely, either spontaneously or under the
influence of therapy.
However, there are a number of conditions which give rise to a
residual defect of short or long duration, leaving the person disable
to a greater or lesser extent.
Disability is defined as any temporary or long-term reduction of a
persons activity as a result of an acute or chronic condition.
8/14/2019 Topic 1 - Theory & Principle of Disease
7/15
ENDEMIC & EPIDEMICENDEMIC & EPIDEMIC
Endemic The constant presence of a disease or infectious agent within a
given geographic area The usual prevalence of a given disease within such area.
Example, malaria
Epidemic
The occurrence in a community or region of a group of illness. Epidemic may include and kind of diseases, including noninfectious
condition
There is no general rule about the number of cases that must exist
for an outbreak to be considered an epidemic.
There is no specification of geographic extent; may cover a few cityblock or an entire nation or worldwide
An epidemic may encompass any time period; it may last a few
hours (chemical intoxication), a few weeks (influenza) or several
years (drug addiction)
Example, AIDS
8/14/2019 Topic 1 - Theory & Principle of Disease
8/15
Pandemic A pandemic or global epidemic is an outbreak of an infectious
disease that affects people or animals over an extensive
geographical area.
Example, H1N1
8/14/2019 Topic 1 - Theory & Principle of Disease
9/15
BASIC CONCEPTS IN INFECTIOUSBASIC CONCEPTS IN INFECTIOUS
DISEASEDISEASE
Reservoir of infection This is where the agent normally lives and multiplies and what it
mainly depends on for survival. This may be human (eg. Chicken pox), animals (eg. brucellosis) or the
environment (eg. Tetanus). It is not necessarily the same as the source of infection in a particular
incident.
Sources of infections Infection may arise from the organisms normally living in
a person, Or those from other human being Or in animal
Or the environment When the sources of infection is inanimate(non living), for example
food, water or fomites, it is termed the vehicle of infection.
8/14/2019 Topic 1 - Theory & Principle of Disease
10/15
Method of spread The routes by which an infectious agent passes from source to host
can be classified as follows:1. Food
2. Direct or indirect contact3. Percutaneous infection
4. Airborne infectious5. Mother to foetus
Food drink or water-borne infection (eg. Typhoid and cholera).
The term food poisoning is often used for incidents of acute disease in
which the agent has multiplied in the food vehicle before ingestion.Example salmonella food poisoning. Or the agent mat have formed
toxins for example botulism.
8/14/2019 Topic 1 - Theory & Principle of Disease
11/15
Direct or indirect contact This includes spread from cases or carriers, animal or environment to
other people, who are contacts.
A carrier is someone who is excreting the organism but who is not ill.
The possible routes includes: Faeces to hand to mouth spread (eg. Shigellosis)
Sexual transmission (eg. Syphilis)
Skin contact (eg. Wound infection and cutaneous antrax)
8/14/2019 Topic 1 - Theory & Principle of Disease
12/15
CAUSATION OF DISEASECAUSATION OF DISEASE
The Epidemiologic Triad The epidemiologic triangle or triad is the traditional model of
infectious disease causation.
It has three components: an external agent, a susceptible host, and an
environment that brings the host and agent together.
Agent, host, and environmental factors interrelate in a variety of
complex ways to produce disease in humans. Their balance and
interactions are different for different diseases.
Host
EnvironmentAgent
8/14/2019 Topic 1 - Theory & Principle of Disease
13/15
CAUSATION OF DISEASECAUSATION OF DISEASE
AGENT FACTORS Agent originally referred to an infectious microorganismvirus,
bacterium, parasite, or other microbe Generally, these agents must be present for disease to occur
They are necessary but not always sufficient to cause disease
HOST FACTORS (INTRINSIC FACTORS)
Host factors are intrinsic factors that influence an individualsexposure, susceptibility, or response to a causative agent
Age, race, sex, socioeconomic status, and behaviors (smoking, drug
abuse, lifestyle, sexual practices and contraception, eating habits)
are just some of the many host factors which affect a persons
likelihood of exposure Age, genetic composition, nutritional and immunologic status,
anatomic structure, presence of disease or medications, and
psychological makeup are some of the host factors which affect a
persons susceptibility and response to an agent
8/14/2019 Topic 1 - Theory & Principle of Disease
14/15
CAUSATION OF DISEASECAUSATION OF DISEASE
ENVIRONMENTAL FACTORS (EXTRINSIC FACTORS) Environmental factors are extrinsic factors which affect the agent and
the opportunity for exposure.
Generally, environmental factors include:
1. Physical factors such as geology, climate, and physical surroundings
(e.g., a nursing home, hospital)
2. Biologic factors such as insects that transmit the agent
3. Socioeconomic factors such as crowding, sanitation, and the
availability of health services.
8/14/2019 Topic 1 - Theory & Principle of Disease
15/15
Thank You
Top Related