COMMUNICABLE DISEASE

It is an illness caused by an infectious agent or its toxic products which is transmitted directly or indirectly to a person through an agency of an intermediate host, vector of the inanimate environment.

EPIDEMIOLOGIC TRIAD:
1. Host – a person upon which a parasite depends for its survival
 Infected – with positive signs and symptoms
 Carrier – carry microorganism without signs and symptoms
 Suspect – suggested person
 Contact – exposed

2. Agent – it includes protozoa, bacteria, viruses and fungi
 Virulent – strength and power of microorganism to cause infection.
 Pathogenecity – capacity of microorganism to cause diseases.
 Infective dose – number of organisms needed to initiate infection
 Organisms specific antigenic variations
 Elaboration of toxins

3. Reservoir (Environment) – the environment in which the agent is found.
 Human – man is the reservoir of diseases that is more dangerous to humans than to other species.
 Animal – responsible for infestations with trophozoites, worms, etc.
 Nonanimal – street dust, garden soil, lint from bleeding, etc.

CONTAGIOUS – Applied to disease that is easily spread directly transmitted from person to person.

INFECTIOUS – are those not transmitted by ordinary contact but require a direct inoculation through a break in the previous intact or mucous membrane.

Mode of Escape From Reservoir
1. Respiratory Tract/ Naso-pharynx
2. Gastrointestinal Tract
3. Genito-urinary Tract
4. Open Lesions
5. Mechanical Escape
6. Blood

MODE OF TRANSMISSION:
 Horizontal – on the same level; example droplet
 Vertical – from top to bottom; example mother and child transmission

There are four main routes of transmission:
1. Contact Transmission
2. Airborne Transmission
3. Vehicle Rout or through contaminated items
4. Vectorborne Transmission

Contact Transmission – sometimes called physical transfer; this is the most common mode of transmission of diseases and infection.


1. Direct contact (Person-to-Person)
2. Indirect contact (intermediary-inanimate objects)
3. Droplet contact
4. Skin break integrity

Airborne Route
1. Droplet nuclei
2. Dust particles in the air
3. Organisms shed into environment from skin, hair, wounds or perineal area.

Vehicle Route – non living things
1. Food
2. Water
3. Drugs
4. Blood

Vectorborne transmission – non-human living things
1. Via contaminated or infected arthropods like mosquitoes, flies, ticks and others.

Host Factors:
Illness following entrance of infection into the body depends on:
1. Age, sex, genetic
2. Nutritional status, fitness, environmental factors
3. absent or abnormal immunoglobulins
4. Status of hematopietic system
5. Presence of underlying diseases