The WHO has defined health but not disease. This is because disease may occur in different varieties ranging from subclinical to severe or fatal illness which may even lead to death. The onset of disease may be sudden or prolonged as in the case of food poisoning and cancer respectively.
image source: newsnetwork.mayoclinic.org
Some diseases are short lived but others may remain for the whole life. The final outcome of the disease may be recovery, disability, illness or death of the person. Fortunately some of the diseases are recovered by it e.g. healing of wound. This ability of healing is known as the natural healing power.
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The term disease has been defined in many ways but an adequate definition of disease is yet to be found. Some of the definitions of disease are given below:
(a) Disease is an abnormal state of body when some of the organ(s) of the body is not functioning in a normal way or properly due to harmful effects of the process.
(b) Disease is “any deviation from function or complete physical or mental well-being”.
(c) Ecologists define disease as an outcome of the disturbance of delicate balance between man and his environment.
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(d) According to dictionary meaning disease is a disorder with a specific cause and recognizable signs and symptoms. The word disease conveys different meanings to different persons.
To the patient it means disease i.e. discomfort or disharmony with his environment; to the doctor it means signs and symptoms and to a pathologist it means one or more structural changes.
The concept of disease has changed with the passage of time i .e. from the supernatural theory to the germ theory and to the theory of multiple causes.
(a) Supernatural Theory:
The pre-historic or primitive man believed that disease was caused due to some supernatural powers or bad spirits that inhabited animals, plants, water and air etc.
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Therefore in this age the treatment of diseases was based on religion, magic and tantras mantras. Though the science has advanced to a great extent but still people believe in magic and tantra mantara and some of the diseases are cured by worshipping the Almighty God.
(b) Germ Theory:
In early 20th century with the advancement of science and study of microbiology it was put forth that the diseases are caused by micro-organisms that enter into the body of the host and not due to evil spirits or bad air. Bacteria and germs are the sole causes of diseases.
(c) Theory of Multiple Causes:
According to this theory the diseases are caused not only due to one reason but there are a number of causes which may include social, economic, cultural, psychological and environmental.
There are a number of diseases which are caused by different reasons and tuberculosis is a representative disease which is caused by multiple reasons like poverty, malnutrition, poor hygiene, poor housing, overcrowding, illiteracy etc.