1. Non-Communicable Diseases:
These diseases are caused by some specific factors.
They remain confined to a person and do not spread.
(i) Degenerative Diseases:
Normally heart, lungs and diseases of central nervous system occur due to insufficient growth of organs.
(ii) Deficiency Diseases:
These occur due to malnutrition.
Allergies occur due to hypersensitivity to foreign substances.
It occurs due to uncontrolled growth of tissues.
(v) Diseases by Agents:
These diseases occur due to physical agents like, heat, cold etc.
(vi) Diseases by Mechanical Agents:
These diseases occur due to mechanical factors like injury, friction etc.
(vii) Metabolic Diseases:
They occur due to metabolic disorders.
According to Sir Francis Galton (1883, Father of Eugenics), it is the, “study of agencies under social control that may improve or impair the racial qualities of future generation either mentally or physically.”
Improvement of human race can be done either by:
(i) Encouraging desirable genetic qualities by breeding.
(ii) Suppressing harmful genes preventing such breeding.
(ix) Gene Therapy:
It is the therapeutic treatment to suppress the genetic diseases. From amnio-centesis nearly 30 genetic disorders can be revealed. So these defective types of foetus can be aborted.
2. Communicable Diseases:
These diseases are mainly caused by different organisms. They spread in a society. So they are called as communicable or infectious diseases. These diseases spread through food, water, air, touch and blood. Some of these diseases are highly epidemic in nature. Therefore it is of great concern to the society.
The communicable diseases can be studied under three aspects:
Even before the invention of microscope the involvement of micro-organism in the disease was suspected. Louis Pasteur and Robert Koch put forwarded the germ theory of the diseases. Pasteur demonstrated that the micro-organisms are responsible for many diseases in animals. Later Robert Koch isolated the bacteria, causing the disease, anthrax. He identified a set of four conditions that had to be satisfied before a particular pathogen is attributed to a disease.
1. The organisms must be regularly found in the animals that have the disease.
2. It must be isolated and grown in pure culture on artificial media.
3. When a healthy animal is inoculated with this culture, it must develop the disease and show the characteristic symptoms.
4. The same organism must be recovered from the inoculated animal.
Applying Koch’s postulations causative organisms of tuberculosis, cholera, typhoid and diphtheria were identified. Later diseases like chickenpox, small pox, and measles were found to be caused by viruses. Gradually other agents like, protozoa, helminthes, were identified as disease causing organisms. Parasitology was a boon to medical science. It helped to treat different diseases. Parasitology revealed the identification of causative organisms, life cycle, host range, and adaptation, which helped in control and eradication of the disease.
It deals with the cause of spread of infectious diseases in the society. John Snow for the first time traced the epidemiology of cholera. Later on epidemiology of other diseases were traced out. It helped to check the spread of disease in a society.
It deals with the self defence mechanism of the body. Edward Jenner (1742-1823), an English doctor noticed that dairymen and milk maids hardly suffer from small pox. He observed that they suffer from a mild disease called cow pox, infected from their cows.
Jenner collected some fluid from the sore, caused by cowpox and injected it to a healthy boy named James Phipps on 14th May, 1776. The boy suffered from cowpox and it healed after some days. After two months, Jenner boldly injected small pox fluid into James Phipps, and the germs could not induce the disease even after repeated inoculation. This led Jenner to prepare vaccines for small pox.
Immunity of our body is caused by the production of antibody developed in response to antigen. Any foreign germ when enters into the body produces antigen. The body produces specific antibodies to a particular antigen. The antibodies destroy the antigens. The understanding of immunity has helped the scientist s to prepare vaccines against many diseases.