The human body has a natural defence mechanism against diseases. It fights against the entry of disease causing microbes through the physical barriers like our skin, tears, saliva, nasal secretion, digestive juice and lymphoid tissue. All the points of entry of disease-causing germs are well-guarded by our body’s defence system naturally.
When the disease-causing germs enter the body, the body sets up its own defence first. Antibodies are produced in the body to kill these germs and these lifeless germs are swallowed by white blood corpuscles. The main function of white blood corpuscles (leucocytes) in the blood is to help defend the body against a sudden attack of germs. For this purpose, the leucocytes change their shape and go into the tissues. They are then called phagocytes. Then they engulf the invading germs and block their spread to other organs of the body, thus sealing the infection.
For example, during an invasion of the “appendix” by the germs, the leucocytes increase in number and immediately send an army of them to the place of attack.
The production of antibodies to fight against disease causing microbes depends upon the health condition of our body, mainly on the nutrition status. The protective foods namely proteins and vitamins control the ability of the body to produce these antibodies. An undernourished person or a person in poor health, in fatigue and with severe physical and mental strain cannot fight the germs effectively. This will lower the resistance to infections and this lack of resistance to a disease is called susceptibility.
We are all exposed to disease causing germs throughout our life. These germs are present in all of us, but only a few of them can cause the disease because of our defence system.
Immunity is that condition existing in the body which protects it against certain diseases.It means resistance to a given germs of a given disease.
For example if a number of persons are exposed to a particular infection, some may catch the disease and some others may not. Those who do not catch the disease are resistant to the disease or immune. This is brought about by antibodies, which are also called immune bodies.
There are two types of personal immunity
1. Natural or inborn immunity
2. Acquired immunity
Natural immunity is the resistance offered by the body under normal conditions without any previous infection or external stimulation like vaccination or inoculation. It is either possessed from birth or acquired during growth.
Certain species are immune to certain diseases. For example, hen do not suffer from tetanus; dogs, rats and mice do not suffer from tuberculosis. This is known as species immunity.
Acquired immunity may be active or passive It is called active, when it has been brought about by
- Having had the disease, i.e, by a previous infection, for example, a previous attack of small pox.
2. Slight infections from repeated exposures to a disease.
3. As a result of inoculation or vaccination with killed or inactivated (made harmless) germs or their products (toxins).
Natural Acquired Immunity: It is called natural acquired immunity when an attack of disease gives a certain amount of immunity from another attack of the same disease as in the case of smallpox.
Artificial Acquired Immunity: It is called artificial acquired immunity when it is due to inoculation of certain material containing antigens. It gives protection against future exposure to that particular disease for a certain period.
Examples: vaccination against smallpox, diphtheria,whooping cough and tetanus.
Passive Immunity: It is called passive immunity if antibodies produced in some other person or animal of the same or another species are introduced into the body to fight the disease. In this case immunity lasts only for a short duration. This is helpful when antibodies are not present in the body.
Example: Mother supplies antibodies to her foetus.
In some cases of passive immunisation, certain violent reactions like asthma, migraine,eczema and skin rashes may occur in the individual which is termed as allergic reactions.
In some cases, there will not be any violent reactions for the first dose, but the individual is rendered intolerant to a second dose. This condition is known as “anaphylaxis”. This is characterised by severe shock, followed after some days by skin rashes,joint pains and swelling.
Doctors take adequate precautions to avoid this condition by giving a small test dose in the skin and studying the reaction to it.
By herd immunity it is meant that a group of people or community as a whole are immune to a particular disease. This happens when more than 70 percent of the people composing the community are immunised against a disease. The other 30 percent, although susceptible, enjoy freedom from that disease by virtue of their belonging to that group. It is, therefore, more important than individual immunity.
Immunization plays a very important role in the prevention of certain communicable diseases.
By immunizing, individuals get protection through artificial acquired immunity and use some immunizing agents for this purpose.
Example: Smallpox eradication
In the case of Cholera, vaccination must be taken whenever there is a threat of Cholera epidemic.
T.A.B vaccination needs to be taken whenever there are typhoid cases in and around your home and when there is a threat of an epidemic.
For tetanus, first dose is given to a pregnant mother during 16-20 weeks of pregnancy and the second dose during 28-30 weeks of pregnancy.
Finally, inspite of all these measures, if the disease is developed, doctors have many remedies in these days to help in the body’s defence againt the disease. And they use mainly antibiotics for this purpose.which are proven to be of great value in a number of diseases.
They need to be used cautiously as there will be some hazards in their use.
However, as prevention is always better than cure, health authorities have built up more defences against disease development. Advancements in medicine have made it possible to manufacture protective substances in the form of vaccines which when injected into the body, will afford protection against subsequent attack and thus give greatest benefit to the mankind.