Active and Passive immunity in animals

Active Immunity in animals

Active immunity involves both the cell-mediated and humoral immunity as well as the innate immune system. Active immunity is induced in the host itself by the antigen, and lasts for a longer period of time.

Types of active immunity

Naturally acquired active immunity

Naturally acquired active immunity occurs when an individual is exposed to  live pathogens, and develops antibodies against specific pathogens which leads to immunological memory.

In some cases, the immunity may be life-long as in the case of small pox, measles, chicken pox, yellow fever etc. while in some others the immunity may be lost after only a few years (e.g., diphtheria, tetanus) or even for lesser period (e.g., influenza, pneumonia).

Artificially acquired active immunity

Artificially Acquired Active Immunity occurs when an antigen is intentionally introduced into a body to be immunized, the latter develops immunity .e.g., vaccine, toxoids.

This immunity is artificial because the antigens are intentionally or purposely introduced, and it is active because the recipients immune system synthesizes antibodies in response. Vaccines provide usually long-term immunity.

Killed and attenuated strains of bacteria and viruses are widely used forms of immunization against many diseases.

Passive Immunity in animals

Passive immunity is the transfer of active immunity, in the form of readymade antibodies, from one individual to another.

Passive immunity provides immediate protection to the individual, but the duration of passive immunization is relatively short, a few days to several weeks when compared to years for active immunity. This is due to the natural degradation of injected antibody from the circulation without internal replacement.

Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and can also be induced artificially, when high levels of human (or horse ) antibodies specific for a pathogen or toxin are transferred to non- immune individuals.

Types of Passive Immunity

Naturally acquired passive immunity

When antibodies produced in the body of an individual (called donor) are naturally transferred into the body of other individual (called recipient), the latter develops immunity, called naturally acquired passive immunity, in its immune system.

This immunity is natural because the transfer of antibodies from donor to recipient occurs under natural conditions, and it is passive because the recipient does not synthesize antibodies but picks them up from the donor.

This type of immunity is significant mainly in the survival of the neonates. The neonate passively acquires antibodies from its mother. The antibodies may pass from the immune mother to the fetus across the placental barrier.

Certain antibodies are also transferred from mother to young ones through colostrum and milk during lactation. These antibodies, called maternal antibodies, remain with the young ones for certain period and after the specified time the immune state disappears. The maternal antibodies generally provide resistance against diseases.

Artificially acquired passive immunity

Artificially acquired passive immunity is a short-term immunization induced by the transfer of antibodies to another individual i.e, produced in one individual or animal and then administered to the other individual, which can be administered in several forms; as human or animal blood plasma, as pooled human immunoglobulin for intravenous ( IVIG ) or intramuscular (IG) use, and in the form of monoclonal antibodies (MAb).

Currently passive immunization is mainly used for prophylaxis following exposure to such diseases as rubella and infectious hepatitis. This is usually accomplished by injecting the patient with gammaglobulin which has been extracted from the blood of immune persons.

Artificially acquired passive immunity is immediate but short-lived (only for two to three weeks . Other examples of this type of immunization are injections of hyperimmune serum and antiserum.

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