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