Artificially acquired immunity is of two types. Either it is an active immunity or it is a passive immunity.

Active imunity, as the name suggests, occurs when the body itself develops antibodies (see Pet Corner 27.7.08) against a specific disease. This can happen in either of two ways.

Firstly, if the animal has been exposed to an infectious disease, it may or may not become seriously ill, but it will develop antibodies against that specific germ. Should the animal recover, those antibodies will protect it from reinfection by that particular germ. This protection varies in length. It may be temporary – as in the foot-and-mouth disease of cattle. In this case, the cattle may be infected several times during their lives. Another such example would be tetanus (‘lockjaw’) in horses. However, the immunity may last longer, even for the animal’s entire life span. Smallpox in humans and canine distemper spring to mind. Once the humans/animals have had a bout of these ailments and survive, they can’t contract these diseases again.

I should mention that in some cases, a long-standing immunity (which an animal obtained after total recovery from a specific disease) can actually weaken in the face of a renewed onslaught by the same infectious agent which returns in increased numbers and with greater pathogenicity (ability to make sick) and virulence (extremely severe and malignant). This happens often with viruses and with some protozoan diseases.

Active immunity can also come from vaccines (artificial inducement of immunity). The germs (viruses or bacteria) present in the vaccine can either be killed germs or can be modified (attenuated = weakened) live viruses or bacteria. Once these weakened (we have taken away their virulence and pathogencity) germs are injected into the body (vaccination), the production of germ-specific antibodies is stimulated, even though the injected germs are ‘attenuated’ (weakened).

The protection which the animal gets after the introduction of the weakened live germ (or even dead germs) may develop slowly, but it is long-lasting and will confer on the vaccinated animal a protection against that particular disease for many months or even many years. In the case of distemper (as with many other diseases), for example, after the first three or four ‘shots’ at three-week intervals, one needs only administer a ‘booster’ vaccination annually.

So far, I have been referring to modified live viruses/bacteria. However, we can use inactivated (dead) germs to build up an immune response to the specific disease that may be caused by that germ when it is alive and kicking and potent. The scientists have many methods at their disposal to inactivate the germs with which the animals are vaccinated. Techniques involving heat or chemicals (formalin, acetone, alcohol, etc) are used.

Lastly, there are new methods of active immunisation which scientists are very excited about. Research in Recombinant DNA vaccines to produce an active immunity is a good example. In this case, genes are manipulated. For example, the viruses that cause canine parvovirus or feline ‘influenza’ can be isolated and ‘recombined’ (incorporated) into certain bacteria. Consequently, these bacteria produce, as a reaction, pure viral protein which can be used as a vaccine. Isn’t science, used for the benefit of mankind, wonderful!
In fact, science can also produce synthetic vaccines that deliver an active immunity. But let me stop here, before I get too carried away and lose track of today’s message which basically was to introduce you to the concept of active immunity.

Next week we will continue with artificially acquired immunity.

Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA’s Clinic and Shelter instead. If you see anyone being cruel to an animal, or if you need any technical information, please get in touch with the Clinic and Shelter by calling 226-4237.

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