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Basic
Vaccinology Pt.1 of 2
Randall
J Berrier, DVM
Staff Veterinarian
Technical Service
Vaccines have
proven to be a major scientific advancement for people and
animals for over a century.
Vaccination is the most efficient, practical and cost
effective means of controlling infectious diseases via
prophylaxis. The
enormity of the benefit from vaccines is hard to comprehend
and is one of the biggest reasons, if not the biggest reason
we as a society currently enjoy our relative good state of
health. Vaccination
has been responsible for the eradication of small pox across
the globe; the elimination of hog cholera and brucellosis from
North America; and the control of diseases such as foot and
mouth disease, pseudorabies, rabies, anthrax and rinderpest
would not have been possible without the use of effective
vaccines.
The general
principle behind the use of vaccines is to introduce a
modified and safe version of a given pathogen into an animal
host which induces an immune response that will be protective
to the animal in the future if and when it encounters a
natural exposure to this pathogen.
There are two basic methods by which an animal may be
made immune to an infectious disease.
One method is passive immunity which produces immediate
but temporary resistance by transferring antibodies from a
resistant animal to a susceptible animal.
Examples of this type of immunity include colostrum
from the dam to the newborn and the use of tetanus and Clostridium
perfringens C & D antitoxins.
The second method of immunization is called active
immunization which involves administering antigens (foreign
substance-vaccine) to an animal so that it responds by
developing its own protective immune response.
Re-immunization or exposure to infection will result in
a secondary immune response.
The disadvantage of active immunization is that
protection is not conferred immediately.
The advantage of active immunization is that once it is
established, it is long lasting and capable of restimulation.
Passive
immunization requires that antibodies be produced in a donor
animal by active immunization and that these antibodies are
then given to susceptible animals in order to confer immediate
but short lasting protection.
Serum containing these antibodies, (sometimes called
serum antibodies, antiserums or antitoxins) may be produced
against a wide variety of pathogens.
The most important role of antiserums is in the
protection against toxigenic organisms such as Clostridium
tetani or Clostridium
perfringens. Antiserums
made in this way are commonly produced in young horses by a
series of immunizing injections.
The toxins of these clostridia are proteins that can be
denatured and made nontoxic by treatment with formaldehyde.
This type of vaccine is known as a toxoid.
Donor horses are first given toxoids, but once
antibodies are produced, subsequent injections of purified
toxin are used and the donor horses produce high levels of
antibodies. The
horses are bled when their antibody levels are sufficiently
high and the serum antibody fraction is separated from the
blood, then processed and dispensed for use in susceptible
animals. Serum
antibodies can be introduced into a recipient animal by
injection subcutaneously and, or intramuscularly, depending on
the product, and in some cases intravenously.
Again, the main advantage to passive immunity (serum
antibodies) is instant immunity to particular disease(s).
The disadvantage is immunity only lasts 10 –
14 days in the
recipient, so repeat doses may be needed.
Serum antibodies serve an important role as part of the
adjunctive treatment of animals that are currently suffering
from a given disease for which the antiserum has antibodies
against. An
example would be treating a horse suffering from tetanus with
tetanus antitoxin.
Active
immunization has several advantages compared to passive
immunization. These
include the prolonged period of protection and the recall of
boosting of this protective response by repeated injections of
vaccine or by exposure to infection.
Ideally, the perfect vaccine should illicit a high
protective immune response with the absence of adverse side
effects. This is
where the challenge for vaccine manufacturers comes in because
these two prerequisites tend to be incompatible in a lot of
cases. Continue to part 2>> |
