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Strangles
By Horse SA www.horsesa.asn.au
Cause
Strangles is the most important infectious disease
affecting horses. It is caused by a bacterium,
Streptococcus equi
Signs
Typically, horses suffering from strangles have
pus discharging from the nostrils and swellings
(abscesses) forming in the lymph glands under
the jaw. These abscesses often burst and exude
a thick yellow pus. Affected horses can have fever,
be depressed and may stop eating.
Most animals recover, but horses that contract
even a mild case of strangles must be isolated
and removed from training or heavy work for up
to 3 months. In some cases the infection can cause
chronic illness or even death.
Epidemiology
Strangles is very contagious, especially with
foals, spreading easily from horse to horse and
often leading to large outbreaks with many horses
affected. It is spread in the discharges (pus)
from the nose and burst abscesses. Objects such
as water troughs, feed buckets, brushes, reins
and other equipment, if contaminated with infected
pus, can also spread the disease. Recovered horses
can spread the disease for up to eight months,
even though they can appear clinically healthy
and normal.
Immunity
In common with other respiratory diseases, such
as canine cough and feline respiratory disease,
immunity is short lived and incomplete. In fact
25% of horses infected with strangles do not appear
to develop immunity. This makes it very difficult
for a vaccine to provide complete protection and
it is not claimed that the vaccine is an absolute
preventative. However, field experience has shown
that vaccination can control the disease by reducing
the degree of clinical disease and reducing the
number of horses affected.
Treatment
Penicillin is the antibiotic of choice against
S.equi. Abscesses may need to be opened and drained
and good supportive care is vital for recovery.
Control
It is strongly recommended that all horses be
included in a regular program of vaccination.
It is particularly important that booster doses
be given prior to periods of greater risk of infection,
such as the breeding or performance season. Pregnant
mares may be vaccinated up to two weeks before
foaling.
Consideration should be given to vaccinating
high risk horses (eg. brood mares, stallions,
performance, pony club, racing and eventing
horses) every six months. In the event of an
outbreak of strangles, horses should be segregated
into three groups and handled as follows:
(a) Those affected by the disease should be
treated, but not vaccinated
(b) Horses with no known contact with the disease
should be vaccinated immediately
(c) Horses known to have been in contact should
be observed for seven to ten days and vaccinated
only if they have a normal temperature and show
no clinical signs of the disease.
STRANGLES: Questions and Answers
Why vaccinate?
Vaccination provides the best possible protection
against strangles which is the most important
infectious disease problem for horses.
Does the vaccine provide 100% protection?
Field experience suggests that a full and regular
program of vaccination for all horses will usually
control or very markedly reduce the incidence
and severity of strangles. However it is not
claimed that the vaccine is an absolute preventative.
Vaccination will reduce the spread in an outbreak
with less horses affected by strangles and those
that do show signs have a milder disease with
shorter recovery and possible protection against
spread through the body.
Thus, vaccination has good benefits and is
the best protection possible. It should be pointed
out that there are other diseases, caused by
different organisms, which may be confused with
strangles.
Can the vaccine be used during an outbreak?
Yes. In the event of an outbreak of strangles,
horses should be segregated into three groups,
Those affected by the disease should be treated,
but not vaccinated. Horses with no known contact
with the disease should be vaccinated immediately.
Horses known to have been in contact should
be observed for seven to ten days and vaccinated
only if they have a normal temperature and show
no clinical signs of the disease.
Does the vaccine cause reactions?
Like a number of other vaccines, Equivac-S or
Equivac 2 in 1 can cause some local swelling
at the site of the injection, especially if
injected subcutaneously and not intramuscularly.
Provided the injection has been carried out
aseptically, any swelling should disappear in
a few days.
What is the vaccination schedule?
When horses and foals are vaccinated against
strangles for the first time, they require a
primary vaccination course consisting of three
doses of Equivac-S or Equivac 2 in 1. The three
doses are given with an interval of two weeks
between injections. Booster doses should be
given at least annually and six-monthly revaccination
should be considered in circumstances where
the risk of infection is known to be high.
What are the signs of strangles?
Typically, horses suffering from strangles have
pus discharging from the nostrils and swellings
(abscesses) forming in the lymph nodes (glands)
under the jaw. Most animals recover, but horses
that contract even a mild case of strangles
must be isolated and removed from training or
heavy work for up to 3 months! In some cases
the infection can cause chronic illness or even
death.
How is the vaccine administered?
The vaccine is injected intramuscularly. The
most convenient site for injection is the centre
of the side of the neck. The needle can be attached
to the syringe and then administered to the
horse. Alternatively, the needle may be inserted
into the muscle and then the syringe attached
and the vaccine injected.
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