In this column veterinarian Dr Liesel van der
Merwe provides practical assistance for common
problems in companion animals. She is a specialist
physician at the Onderstepoort animal teaching
hospital and a senior lecturer in
the section of small animal
medicine. Send your questions to
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 Dr Liesel van der Merwe
Iam going to try and demystify
the whole vaccination process
for all you pet owners out there.
This will involve me taking some
liberties with the exact detail of the
immunological process, so to those
with a bit more knowledge on the
subject, please bear with me.
Antibodies are the “tracker system”
of the body. They are a kind of protein
designed to identify only specific
foreign substances, such as viruses,
bacteria or protein particles in
allergies.
Each pathogen thus has a specific
antibody. Once they have identified
an “intruder”, they attach to it and
flag it for the immune system cells,
which then engulf the foreign substance
and process it to activate the
immune system.
Young animals are not born with
their own antibodies; these only
develop with time due to exposure
to the environment and pathogens.
In humans, the placenta allows mixing
of maternal and foetal blood
and a baby is born with its mother’s
antibodies in the blood to ensure
early protection.
The placenta in animals is not as intimate
and blood is not shared.
Young animals rely on antibodies
which have accumulated in the first
milk (colostrum). Milk contains high
levels of antibodies throughout lactation
in cats, but antibody levels
drop rapidly in other species.
The stomach is normally impermeable
to proteins and the acid
would normally digest proteins but
in the first 12-24 hours after birth
there are gaps in the stomach lining,
allowing antibodies to be absorbed
into the bloodstream of the newborn.
These then provide protection
in the first six weeks of life. It is
thus vital that newborn animals
suckle within the first 12-24 hours
of life.
All proteins in the body have a lifespan
and are recycled, and these
antibodies start decreasing so that
at about six weeks of age they are
no longer very protective. This is
when vaccination plays a role.
Vaccinations are either a “dead”
form of the virus or bacteria, a
modified live or weakened form or
a reconstituted vaccine which uses
only a part of the virus.
Vaccination hardly ever causes disease
in dogs and cats although they
can in animals such as the wild dog,
panda and other wild canidae and
felidae.
The first vaccine can only be given
once the maternal antibodies are
decreasing, otherwise they will identify
the vaccinated pathogen and
block the immune response. This is
why we generally give the first vaccination
at six weeks. If there is a
problem with a disease in a kennel,
we can start at four to five weeks.
This first vaccine primes the body
against the disease. The body has to
identify the pathogen as foreign,
without the benefit of antibodies,
as they are not yet present, and
present it to the cells of the immune
system, which will make specific
antibodies, and make memory cells
against that specific pathogen.
This whole process takes about
three weeks and is called seroconversion.
The reason for the booster
four weeks afterwards and again
four weeks later is to remind the
immune system and thus really
establish a good memory.
In some cases it can also be argued
that the maternal antibodies may
still interfere with the six week vaccination,
so we are really trying to
cover all bases. The rabies vaccination
is usually delayed until after
three months, as maternal antibodies
interfere with the vaccination if
the puppy is younger.
The booster at one year is important
to set the memory as well as
boost the rabies vaccination. The
duration of the immunity or memory
of the body is different for different
organisms – it is long lasting
against rabies, but shorter against
snuffles or kennel cough. Thus each
individual animal has a different
antibody profile depending on their
exact environment and vaccination
status.
The response of a vaccinated animal
to a virus is much quicker, as the
virus is identified earlier and memory
exists. Antibodies are quickly
made as the “recipe” is already
known, whereas in an unvaccinated
animal the immune system first has
to identify the virus without the
help of antibodies, break the virus
into bits to find the recipe required
to identify it again and then programme
cells to make this antibody.
This time lag will allow the infection
to become established in the body.
Vaccinated dogs are primed to identify
and destroy, thus preventing
establishment of infection.
Vaccinations do not work very well
in dogs which are malnourished and
in animals with a compromised
immune system and drugs such as
chemotherapy and cortisone will
also reduce efficacy. |