community

1. Natural history of disease
Presented by
Deepa Manandhar
Lecturer
Community Health Nursing

2. Introduction
• Disease results from a complex interaction between
man, an agent (or cause of disease) and the
environment.
• In the absence of any intervention i.e. prevention or
treatment, all diseases follow a natural course of
events which refers to “Natural History of Disease”.

3. Introduction…
• Refers to the progress of a disease process in an
individual over time, in the absence of intervention.
• History of disease is a key concept in epidemiology.

4. Introduction…
• The natural history of disease occurs in two phases
Prepathogenesis phase (the
process in the environment)
Pathogenesis (the process in
the man)

5. PREPATHOGENESIS PHASE
• Disease agent has not entered man, but factors
favouring disease exist in the environment.

6. PREPATHOGENESIS PHASE
• The mere presence of agent, host and favourable
environmental factors in the prepathogenesis period is
not sufficient to start the disease in man.
• What required is an interaction of these factors to
initiate the disease process.

7. PATHOGENESIS PHASE
 This phase begins with entry of disease "agent" in
susceptible host.
 Entry of disease agent in susceptible human host.
 Disease agent multiplies and induces tissue and
physiological changes.

8. PATHOGENESIS PHASE
 final outcome- recovery, disability or death.
 This phase may be modified by intervention measures
such as immunization, chemotherapy
 In this phase, the infection may be clinical or
subclinical; typical or atypical; host may be carrier
with or without having developed clinical disease

9. PATHOGENESIS PHASE
 In chronic diseases (coronary heart diseases,
hypertension, cancer), this phase is referred as
presymptomatic phase in which there is no manifest
disease.

10. PATHOGENESIS PHASE
 Clinical stage begins when the recognizable sign and
symptoms appear with the time and the disease phase
is already advanced into the late pathogenesis.
 In many chronic diseases, the agent-host-
environmental interactions are not well understood.

11. Natural History of disease

12. • PATHOGENESIS PHASE
• • Entry of disease agent in susceptible human
host.
• • Disease agent multiplies and induces tissue
and physiological changes.
• • final outcome- recovery, disability or death.
• This phase may be modified by intervention
measures such as immunization,
chemotherapy