EPIDEMIOLOGICAL TRIAD

ENVIRONMENT

AGENT HOST

AGENT

• The first link in the chain of disease transmission is a

disease agent.

• The disease agent is defined as a substance, living or non

living or a force, tangible or intangible, the excessive

presence or relative lack of which may initiate or

perpetuate a disease process.

• A disease may have a single agent, but more factors are

responsible for disease transmission.

BIOLOGICAL AGENTS

• VIRUS

• BACTERIA

• PROTOZOVA

• FUNGUS

CHARACTERISTICS:

- Infectivity

- Pathogenicity

- virulence

PHYSICAL AGENTS

• Exposure to excessive

heat, cold, humidity,

pressure, radiation,

elecricity, sound etc..

CHEMICAL AGENTS

• ENDOGENOUS • EXOGENOUS

MECHANICAL AGENTS

NUTRITIONAL AGENTS

SOCIAL AGENTS

OTHERS

• Hormones

• Lack of part or structure

• Chromosomal factors

• Immunological factors

HOST

• Human being is referred

to as “ soil” and the

disease agent as “ seed”

DEMOGRAPHIC FACTORS

BIOLOGICAL FACTORS

SOCIO ECONOMIC FACTORS

LIFE STYLE FACTORS

ENVIRONMENTAL FACTORS1. PHYSICAL ENVIRONMENT

BIOLOGICAL ENVIRONMENT

PSYCHO SOCIAL ENVIRONMENT