Topic 1 - Theory & Principle of Disease

8/14/2019 Topic 1 - Theory & Principle of Disease

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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


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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


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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)


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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)


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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)


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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.


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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


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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


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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.


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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.


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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)


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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


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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


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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.


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Thank You

Topic 1 - Theory & Principle of Disease

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