Immunity and Immunisation

By immunity is meant the ability of a person to resist a disease. When a disease organism gains admittancetothe tissues of the body it will multiply and either destroy local tissue or produce poisons which will affect the whole body, or both. The ease with which it can do this depends upon the person's immunity.

Immunity may be natural or acquired.

Natural Immunity is the resistance a person possesses to ward off an infectious disease with which he has never before been in contact.

This is partly hereditary and partly due to the state of his health. Nature attempts to counteract antigens, that is invading micro-organisms or other foreign protein substances, by producing its own special protective protein known as antibodies.

To counteract the poisons (toxins) produced by invading micro-organisms, the body also makes antitoxins which are a special kind of antibody.

For each toxin a separate specific antitoxin has to be made.

Our resistance today to tuberculosis is great. It no longer is the scourge of Europe. Those of our ancestors who had no natural immunity died early from the disease, often before having children, and we are mainly descended from those who had the ability to survive.

When Europeans first contacted the Pacific Islanders they brought tuberculosis and measles (as well as other diseases) to these people for the first time. The effect was devastating.

Our natural immunity may be enhanced by getting sufficient sleep and by eating a well-balanced diet including eggs, fish, meat, fruit and milk.

Acquired Immunity. In some diseases we can reinforce a person's natural immunity by vaccinating him so that his body is stimulated to produce plenty of antitoxins which will protect him against that particular disease. This gives Active Immunity because the patient's tissues actively cooperate in the process.

A short-lived form is known as Passive Immunity. The patient is given an injection of serum containing antibodies or antitoxins when there is little or insufficient time for his body to produce the antibodies by the vaccination process.

Active Immunisation. The patient's blood and tissue cells are encouraged to produce antibodies against a particular disease by the administration of killed or attenuated (weakened) micro-organisms, usually in the form of vaccines.

As we all know, some diseases give lasting immunity. One attack of smallpox, tetanus, or whooping-cough will prevent the person from ever catching the disease again.

Other infections like the pneumonias, boils, in-fluenza, and colds do not give lasting immunity. Therefore we can only provide lasting active immunity against the former diseases and not against the latter.

In the case of whooping-cough, the patient may become infected later by a related organism, Para-pertussis, and appear to have a mild ‘second attack’ of whooping-cough.

Today we may actively immunise against certain bacteria, viruses, and rickettsias.

1. Bacterial Diseases. Whooping-cough, tetanus, diphtheria, cholera, typhoid, plague, and to some extent tuberculosis (using B.C.G.).

Immunisation against whooping-cough (pertussis), tetanus, and diphtheria is usually (but not necessarily) performed with a triple vaccine containing all three disease antigens, and may be begun from the age of 3 months; a second and third injection are given after two months then after six months; a booster dose of diphtheria and tetanus vaccine being given at school entry age.

2. Virus Diseases. Smallpox, yellow fever, rabies, poliomyelitis, and measles vaccines are available.

Smallpox vaccination is commonly per-formed with calf lymph. The cowpox virus in the lymph has been weakened by giving it in repeated doses to the animal until its tissues have produced plenty of protective anti-bodies. The weakened virus antigens are located in the serum which is then used for human vaccination.

Primary vaccination for babies is not now compulsory in Great Britain but at the parents' request it is performed early in the second year of the child's life. This confers immunity of a high degree for two to three years and of a lesser degree for many years.

In Great Britain revaccination of children may be done just about school entry and should be repeated at school leaving age-15 to 19.

Revaccination should be undertaken when one is going into an endemic area. This is performed in a manner similar to that for infants and only a slight papule with some itching results.

Poliomyelitis vaccination is very easy to give. The oral vaccine, prepared from live viruses (Types 1, 2, and 3) attenuated or weakened by living for generations in a tissue culture medium, is dropped on to a lump of sugar and swallowed. The recommended course of vaccination consists of three doses, each of three drops, given at the same visits as those for triple vaccine.

Measles vaccination need not be given until a baby is about a year old since it is immune to measles for six months or more owing to the presence of maternal antibodies in its serum.

Rubella (German Measles). The live rubella virus vaccine is offered routinely to all girls between their eleventh and fourteenth birth-days. Immunity is of long duration.

3. Rickettsial Diseases. One may be immunised against typhus if one is travelling through or living in an endemic area.

Passive Immunisation. This is performed by injecting serum which has been prepared, usually in horses, by actively immunising an animal against a specific disease.

Sometimes one may use a serum from a convalescent patient. The serum contains anti-bodies or antitoxins against a particular organism or toxin. This form of immunisation is sometimes of great use in an epidemic.

If a pregnant woman (6 to 12 weeks pregnant) who has not had German measles has contracted, or is in contact with cases of German measles, then it is a wise precaution to passively immunise her. This will prevent her getting the disease and so affecting the faetus. Another instance of its use is against poliomyelitis. Queen Elizabeth II, when touring Australia, was forced to travel during an epidemic of poliomyelitis and so she was passively immunised with human gamma globulin.

When a person is wounded and there is any possibility of dirt in the wound, or the doctor considers it to be tetanus-prone, then an injection of A.T.S. (antitetanus serum) is given. This is to counteract the toxin produced by Clostridium tetani.

It must be repeated that passive immunisation is evanescent and its maximum duration of action is five to six weeks.

Source : Family Physician

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