Immunity is the power to resist and overcome infection caused by particular organisms:
Factors Influencing the Immune status of Individuals: Inherent:
Racial: Some races are susceptible or immune to certain diseases. For example, Hebrews are more resistant to tuberculosis than other people.
Species: Some of the species of animals have resistance to certain diseases e.g. lower animals never get measles or typhoid fever while man is susceptible to get these diseases. Birds do not get infection with certain kind of tubercle bacilli, which affects cattle or man.
Individual: some people have a strong natural resistance or immunity to certain diseases. This is known as individual immunity.
Types of Immunity
Natural immunity: Natural immunity results after acquiring certain diseases like measles, and usually lasts a life time.
Artificial immunity: Artificial immunity follows the receipt of a vaccine such as polio vaccine.
Active immunity: Non-virulent microorganisms are injected as antigens and the body produces antibodies against the antigen.
Passive immunity: Immunoglobulins or antibodies are injected as a vaccine to neutralize to antigen.
Acquired immunity: Acquired immunity may be natural or artificial.
Acquired artificial immunity:
Immunity which, is acquired artificially by introducing vaccine and toxoid (active) and serum (passive) is known as acquired artificial immunity.
Acquired natural immunity:
People who suffered from disease will have immunity against that particular disease e.g. small pox. This is known as acquired natural active immunity.
Acquired natural passive immunity.
The child gets antibodies from its mother through placenta and breast milk and has immunity for sometime against certain diseases.
Types of Immunisation
Active immunization: It implies administration of antigenic preparation in order to stimulate production of antibodies within the tissues of the individual. This is known as active immunity. The material used for producing active immunity are vaccines (e.g.) BCG vaccine.
Passive immunization: Sera containing specific antibodies are directly injected to produce passive immunity. Eg. Anti-toxin sera in diphtheria (prepared from horse serum) and tetanus immunoglobulins.
Vaccines may consist of:
Live, virulent organism in sub lethal doses (e.g.) cholera vaccine, anti-rabies vaccine.
Live attenuated organisms - e.g. vaccine for small pox, tuberculosis (BCG) and yellow fever.
Dead organisms e.g. vaccines of typhoid, cholera and plague.
Toxins of organisms, such as toxoids - e.g. vaccines for diphtheria, tetanus and scarlet fever.