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EQUINE REVIEW
AUTUMN 2010
10
The bacteria become active and multiply in
poorly oxygenated (anaerobic) conditions.
Deep puncture wounds or bruised tissues with
a poor blood supply create these anaerobic
conditions. This is why puncture wounds of the
foot, which have a high probability of being
contaminated with soil, are the classic injury
that leads to the onset of the disease. Other
high risk infection routes occur at foaling:
firstly in mares, through contamination of the
uterus and secondly in newborn foals, through
the umbilicus.
As the bacteria multiply they produce various
neurotoxins and it is these, especially one
called tetanospasmin which cause the clinical
signs seen with the disease. The toxins spread
along nerves and through the blood stream to
the CNS where they bind to nerves causing
continuous stimulation of the muscles they
supply. Horses are very sensitive to the effects
of the toxin and it takes only small amounts to
cause disease. The time taken for symptoms
to appear after injury is generally 7-21 days
but can be longer, by which time the original
wound may have healed and been
forgotten about.
Symptoms follow a progressive spasm of
muscles and increased sensitivity to noise and
sudden movement. Initially horses may appear
stiff, not wanting to move or lower their neck
to graze, this then leads on to a more definite
rigid ‘sawhorse’ stance with the tail head
raised. The horses' expression can take on a
tense appearance as contraction of the facial
muscles pulls back the lips, flares the nostrils,
widens the eyes and makes the ears stand
erect. Spasm of the third eyelid muscle causes
it to protrude across the eye and involvement
of the jaw muscles prevents the horse from
opening its mouth, leading to the old name for
this disease of ‘Lockjaw’. Loud noise or sudden
movement will exacerbate the signs bringing
on bouts of severe spasms. Eventually the
horse will collapse with convulsions and death
will follow due to respiratory failure.
Animals' suffering from tetanus have a poor
prognosis and once clinical signs are
advanced treatment is rarely successful.
Treatment, when attempted, is aimed at killing
the bacteria, neutralising the neurotoxins and
giving symptomatic and nursing care.
Penicillin is effective at killing the bacteria and
will stop more toxins being produced. Tetanus
antitoxins will mop up any free toxin in the
blood stream however it has no effect on the
toxins that are already bound to nerves, so the
nerve damage cannot be reversed. This is one
of the main hurdles to effecting a recovery.
Sedatives and muscle relaxants as well as a
dark, quiet stable can help control spasms.
Where the chances of recovery are very poor,
euthanasia on humane grounds may well be
more appropriate than attempting to treat.
EQUINE
TETANUS
Tetanus is definitely a disease you want to
take steps to prevent and this is easily done
by vaccination. Vaccination with tetanus
toxoid gives good long lasting protection.
The protocols for vaccination are outlined
below. Mares and foals are special cases
and are outlined separately.
Tetanus antitoxin can be used to give
immediate but short term protection. It is
commonly given to foals at birth, injured
animals or animals undergoing surgery
where there is no history of vaccination
or the history is unknown.
Horses and ponies
Those previously not vaccinated, or with
an unknown vaccination history, or overdue
for vaccination booster should receive...
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Primary course of two injections
4 - 6 weeks apart
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First booster 12 months after primary course
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Follow up boosters every 2 years
Pregnant Mares
Ideally the mare will have received the
primary course and be up to date with
boosters prior to becoming pregnant. A
booster given 4-8 wks prior to foaling will
then provide high levels of passive immunity
to her foal via the colostrum. This passive
immunity will protect the foal for up to
6 months.
Foals need careful consideration
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The umbilicus of the new born foal is a
potential entry point for infection. So they
are high risk.
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The immune system of the foal cannot
respond to vaccination until
3-4months old.
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Passive immunity from maternally derived
antibodies (MDA) absorbed from the
mare’s colostrum will protect the foal up to
6 months old but will also interfere with
response to vaccination during that time.
Therefore:
1
Foals born to unvaccinated mares or foals
not receiving colostrum should be given
antitoxin at birth. The primary vaccination
course can then be started at 3-4 months.
2
Foals born to mares of unknown
vaccination status and foals receiving
poor quality colostrums should be given
antitoxin at birth. The primary vaccination
course can be started at 3-4 months but
should be repeated at 6 months in case
of interference from MDA.
3
Foals from mares that received a booster
4-8 weeks prior to foaling and having
good quality colostrum can rely on MDA
to protect them up to 6 months old and
can start the primary course at 6 months.
As well as vaccination, reducing the risk
of injury and prompt attention to wounds
are important.
Avoiding contact with objects and structures
that could possibly cause injury is another
important preventative step. So make sure
your horse lives in a safe, clean and tidy
environment whether that be in the stable
or out at grass.
When wounds do occur cleaning and first
aid are essential. These should be done
as soon as possible. Deeper wounds may
require flushing and drainage, with antibiotic
therapy as appropriate.
Tetanus, thanks to widespread vaccination
is a sporadic disease, however it is an
ever present risk. Remember horses are
particularly susceptible due to their close
association with soil, their athleticism
and increased chance of injury and
their sensitivity to the toxins. So don't
be complacent:
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Assume the bacteria are out there
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Accept that treatment is often unsuccessful
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Arrange for vaccination!
Prevention...
Tetanus bacteria
A donkey with Tetanus