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Strangles is a disease caused by the bacteria Streptococcus equi. The name comes
from the fact that it enlarges the lymphnodes between
the jawbone, causing the horse to make strangled
breathing sounds. The bacteria only causes disease in
equine species (horses, ponies, donkeys and mules).
It’s not dangerous for other animals or humans, but
strangles is often associated with facilities that
experience a high turnover of horses (fairs, horse
sales, competitive events, boarding stables). It
is one of the most common equine respiratory
infections in the world and it can affect horses of
all ages and types. Young horses are particularly
susceptible. Most animals recover from strangles with
no long-term aftereffects.
Some horses are carriers of S.equi, meaning that they are
infected with S.equi but do not show any signs of the
disease. Carriers of S. equi can be a source of strangles
for susceptible individuals.
The disease causes major economic losses to the equine
industry worldwide due to its prolonged course, extended
recovery period and associated serious complications. In
Sweden, where strangles and equine flu are notifiable
diseases, there are approximately four cases of strangles
for every case of flu.
Strangles itself can kill (in simple cases there is a one
percent mortality rate), but the major reason for its
concern is the speed with which strangles spreads among
horses, especially in a stable setting. In large horse
populations, established outbreaks may last for months,
essentially shutting down stabling premises.
Moreover, “recovered” horses (carriers) can harbour
Streptococcus equi with no outward clinical signs.
Consequently, new or recurrent outbreaks are likely unless
costly diagnostic procedures and aggressive quarantine
measures are used.
Strangles is caused by oral exposure of a horse to S. equi
bacteria. The bacterium enters the lymph glands via the
respiratory tract and may harbour in the guttural pouch.
Horse-to-horse contact (pus or nasal discharges from an
infected horse is the easiest way) but strangles can also
be spread through contaminated tack and equipment, shared
drinking bowls and feed, clothing and hands. It is thought
that the bacteria can survive in water for at least four
weeks, and up to eight weeks on tack or wood.
Flies may also spread the bacteria from horse to
horse. The bacteria can survive in the environment
for weeks or months. Exposure of a horse to S. equi
does not necessarily mean that it will come down with
Previously exposed horses are often immune to the disease,
or do not get as sick as unexposed horses. During the first
three to six months of life, foals are often protected by
maternal antibodies. Vaccination can also increase
resistance to the disease.
Stress (poor nutrition, overcrowding, lengthy
transportation or pre-existing diseases) increase the risk
• The incubation period (time from exposure to first signs
of disease) is 3 to 14 days with abscesses formed up to 2
weeks following infection. The horse has fever (sometimes
41 degrees Celsius or 102 degrees Fahrenheit!), has
decreased appetite and is depressed.
• There is a watery nasal discharge that quickly turns
thick and yellow.
• The lymph nodes in the upper-respiratory tract become
enlarged, the ones between the jawbones being the most
noticeable. The inflammation is due to the accumulation of
purulent fluid (pus) within the lymph node.
• Affected horses may stand with neck outstretched to
relieve pressure in upper neck. Later in disease, lymph
nodes often burst and drain pus from openings in
Complications of disease are seen in 10 to 20 percent of
cases (these should be considered emergency
situations requiring immediate veterinary
care). Difficulty in breathing and signs of distress
due to compression of trachea by enlarged lymph nodes in
the neck. This can lead to death by asphyxiation
(source of the name “strangles”) and may require emergency
lymph node drainage or insertion of a breathing tube
through the trachea.
Occasionally, abscesses spread by internal relase of pus to
other parts of the body: the lungs, the abdominal cavity or
even the brain. This is lifethreatening and known as
internal or “bastard” strangles.
Purpura hemorrhagica (widespread small bleeding
along with fluid accumulation (oedema) of the limbs, eye
lids and gums) may occur in association with circulating
antibody complexes with S. equi M-like protein. The
peripheral accumulation of fluid can be so extreme that
circulatory failure and death ensue. Strangles is often
fatal in young foals (less than six months old) that did
not receive sufficient colostral immunity as newborns.
Strangles is sometimes considered to be a disease of foals
and young adult horses. Older horses are often
immune to strangles due to prior exposure during their
youth, or they may display only lethargy and nasal
discharge without obvious lymph node swelling (however,
these animals can still spread the disease).
Atypical strangles presents as ‘flu-like symptoms, which is
a complication that becomes persistent on a yard.
Although strangles can be diagnosed based on symptoms
alone, it can be confirmed by identification of the
Sterptococcus equi in fluids from the throat, nasal
passages or abscesses.
Treatment of strangles depends on the stage of the
disease. Although S. equi is usually sensitive to
antibiotics such as Penicillin, antibiotic treatment is
generally discouraged if a horse is already exhibiting
signs of disease such as fever and nasal discharge. Once
the lymph nodes become enlarged and abscessed, treatment
with antibiotics will only prolong the disease. Antibiotic
treatment at this time may increase the risk of
complications such as internalized abscesses.
Antibiotic treatment of strangles-exposed horses before
they display signs of disease may reduce the rate
of morbidity (percentage of sick animals). This is
still a controversial subject and the final decision should
be left to your veterinarian. In contrast,
complicated cases of strangles may require intensive
antibiotic and supportive veterinary therapy to
save the horse’s life.
• Observe sick animals for signs of shock, high fever
(above 103 degrees F), and difficulty in breathing
or abnormal swelling of the legs or ventral abdomen.
• Swollen lymph nodes may be softened by the application of
hot compresses. This may hasten abscess
drainage. Large abscesses that interfere with
breathing may be lanced under veterinary supervision.
• If the horse is cooperative, draining abscesses may be
cleaned with dilute antiseptic washes to promote skin
healing and avoid secondary infections.
Once the first case of strangles on a yard has been
diagnosed, all other horses will be at risk.
The affected horse needs to be isolated from the other
horses. The yard should be closed to horses from outside.
All healthy animals on the yard should be monitored closely
to pick up new cases of strangles as early as possible.
People who are in regular contact with horses from outside
the yard should stay away from the infected yard as much as
Effectively, this could mean that a yard will be closed
down. Unfortunately, this situation can last for months.
Several measures can be taken to minimise the risk of
strangles on a yard:
• Try and avoid contact with horses of unknown origin.
• Make sure a yard doesn’t become overcrowded.
• If horses are introduced, keep them in quarantine for a
few weeks to observe the onset of any clinical signs. Care
must then be taken with personnel attending the isolated
horses – they must not move from the isolated horses to the
other horses on the establishment.
• Reduce sharing of tack or equipment from horses of
unknown health status.
• Restrict movement of people onto the premises who have
arrived from an affected yard.
• Minimise the risk of horses on the yard coming into
physical contact with horses on neighbouring yards whose
health status is not known.
contact with other horses (left). Vaccination into the
upper lip of a horse (right)
Vaccinate if the horse is at risk of contracting the
disease, and ensure that new animals arriving onto the yard
have an up-to-date vaccination program. Vaccination as part
of good stable management forms a critical element in
preventing strangles outbreaks on yards.
A vaccine is now available to reduce
clinical signs and the incidence of lymph node
abscesses. The vaccine can be used in horses from just
four months of age and is administered by
administering a very small volume of vaccine into the
upper lip of the horse. After vaccination, a small
pimple will develop on the inside of the lip. This is
perfectly normal and will disappear within a few days.
Where vaccination is required and to minimise the risk of
strangles taking hold, all horses in a yard should be
The basic vaccination schedule is two submucosal
vaccinations four weeks apart.
Horses in high-risk situations should be revaccinated with
a single dose every three months.
For horses in medium-risk situations revaccination every
six months rather than every three months can be
considered. If horses are revaccinated every six months, a
prompt booster with a single dose should be given if an
outbreak of strangles occurs more than three months after
the last booster (see table).
There is generally no need to vaccinate horses in low-risk