Natural history of disease

NATURAL HISTORY OF DISEASE

Description also available in video format (attached below)

Introduction

• It refers to the progression of a certain disease in a person over a period of time, in the absence of  treatment of that disease. For an example, untreated HIV can cause several clinical problems at its beginning stage and if we don't treat it then it can progress to AIDS and usually death.
• It is a concept of epidemiology which signifies the way in which a disease evolves itself over a period of time and also helps us to understand the pathogenetic chain of events for a specific disease and its preventive measures.

Principal Model

The framework of natural history of disease can be easily understand in two phases:-

1) Prepathogenesis phase

• It refers to the period prior to the beginning of a disease. In this phase disease causing agent has not yet entered in a person but the factors that can help the interaction of a causing agent & human host already exist in the environment. 

• For an example, Smoking, alcohol, radiation, pollution etc are the factors that can lead to the cancer.
• This situation is also known as the "Man in the midst of disease" or "Man exposed to the risk of disease".

The causative factors of disease can be classified as:-

1) Agent factors

It can be easily defined as the factors whose excessive presence or relative absence can be easily lead to a condition known as disease and these are further classified as:-

a) Biological agents

• Bacteria
• Fungi
• Viruses etc.

b) Nutrient agents

• Carbohydrates
• Vitamins
• Minerals etc

c) Physical agents

• Heat
• Cold
• Humidity etc

d) Chemical agents

• Urea
• Fumes
• Gases etc

2) Host factors (Intrinsic)

All the characteristics of a host that affect the susceptibility to disease, especially in comparison to the other hosts and these are further classified as:-

a) Demographic characteristics

• Age
• Gender
• Ethnicity etc

b) Biological characteristics

• Genetic factors
• Blood groups
• Immunity etc

c) Socioeconomic characteristics

• Education
• Stress
• Occupation etc

3) Environmental factors (Extrinsic)

All the factor in which we live or work and that can increase the risk of disease and these are further classified as:-

a) Physical environment

• Air
• Water
• Soil etc

b) Biological environment

• Microbial agents
• Rodents
• Insects etc

c) Psychosocial environment

• Values
• Habits
• Religion etc.

2) Pathogenesis phase

• This phase refers to the sequence of events that begins from the entry of a causing agent and end at recovery, disability or death. 
• Let's understand this by the help of an example-

"Pathogenesis of Malaria"

1) Causing agent in the host

• Female Anopheles mosquito helps the causing agent "Plasmodium falciparum" to enter in the human host by biting him.

2) Growth of agent in host environment

• After getting entry in human host the parasite of malaria starts reproducing in liver & blood stream because of its favorable environment.

3) Progression of disease

• As the number of parasites increases in the host because of reproduction, it leads to the progress of infection in blood stream and results in symptoms like chill, sweating, dry cough etc.
• If a host get a proper treatment, the infection can be control otherwise it can lead to the death.

4) Transmission of disease

• In last the infection can be easily transmitted from the infected host to the non infected one by the help of a vector known as female Anopheles mosquito.

Video description

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