- What is Strangles?
- Strangles is a contagious, bacterial
disease of the horse caused by the bacteria Streptococcus
- S equi enters the horse’s
system via the mouth or nose and invades the mucosa of the
pharyngeal region and upper respiratory tract.
- S equi can also infect and be
harbored in the guttural pouches.
- The name ‘Strangles’ originated
because swelling of the lymph nodes under the jaw can cause
the horse to have difficulty eating and breathing. ‘Bastard
Strangles’ is characterized by internal abscesses, and can
sometimes be very difficult to diagnose.
- The disease is extremely contagious,
but not usually fatal in most horse populations.
- What are the clinical signs of Strangles?
- Classic infection with S equi
is characterized by fever, enlarged lymph nodes (especially
under the jaw) which may abscess and drain thick nasal
discharge, anorexia, and depression.
- Fever is the first sign; followed
closely by enlargements of the lymph nodes in the head/neck.
- The most obvious and well-known
clinical sign is abscess formation under the jaw; these
abscesses will mature and eventually drain thick,
- HOWEVER, remember that a horse can be
infected with S equi without visible abscesses!
- ‘Bastard’ strangles is characterized
by internal abscesses; these horses are often off their
feed, depressed, lethargic, febrile, etc.
- How is Strangles transmitted?
- The most obvious source of
transmission of S equi is nasal discharge and pus
draining from submandibular abscesses of infected horses.
- The bacteria can be transmitted
directly and indirectly. Direct transmission is via
horse-to-horse contact. Indirect transmission is via
sharing of water/feed buckets, tack, water sources,
- Occasionally, apparently healthy
horses can shed the bacteria in normal-appearing nasal
secretions, thereby acting as a source of infection for the
rest of the herd.
- Nasal shedding of the bacteria usually
starts 1-2 days after development of fever, and can persist
for 2-3 weeks beyond the resolution of clinical signs. Some
horses become persistently infected, and may shed the
bacteria intermittently for years.
- S equi can persist in the
environment and act as a source of re-infection to
- How is Strangles diagnosed?
- Bacterial culture of nasal swabs,
nasal washes or pus from draining abscesses is the gold
standard for diagnosis of S equi infection.
- PCR testing is used to detect the DNA
of S equi in swabs or washes from suspect horses
- PCR cannot distinguish between dead
and live organisms. Thus, culture is used to confirm
infection in PCR-positive cases.
- Serology (blood work) can be useful in
working up cases of bastard Strangles
- How is Strangles treated?
- The recommended treatment of Strangles
is directed at encouraging maturation and drainage of
abscesses. This can be accomplished via hot compresses,
topical treatments (icthammol) and surgical drainage.
- Fever and pain can be managed with
oral anti-inflammatory medication (bute, banamine).
- There is significant debate about use
of antibiotics in the treatment of active Strangles
infections. Once the abscesses have formed, antibiotic
therapy may actually slow the maturation of the abscesses,
ultimately slowing progression and resolution of disease.
Is there a Strangles vaccine?
- Antibiotics may be most useful very
early in the disease process and/or in those horses that are
severely affected (i.e. having trouble eating, drinking or
- Some severely affected horses require
intensive care in a hospital setting.
How can I keep my barn as safe as
- Currently, the recommended vaccine is
an attenuated live vaccine that is administered intranasal
to stimulate local immune response in the pharyngeal mucosa.
- An intramuscular vaccine is available,
but not generally recommended due to high rate of
complications (abscesses, sore necks).
- The intranasal vaccine should not be
administered at the same time as other intramuscular
vaccines, due to risk of abscessation at injection sites.
- The intranasal vaccine is given in an
initial 2-dose series, 2-3 weeks apart, followed by annual
- Vaccination should not be used during
an outbreak except in those horses that have had no contact
with infected or suspect horses.
What do I do if I suspect a case of
Strangles in my barn?
- Use common sense! Keep new arrivals
isolated for 2-3 weeks before joining the herd. Keep
resident horses away from those just visiting the farm.
- Don’t allow direct contact with
unknown horses while at shows, events, trail rides, etc.
- Minimize stress associated with
excessive work, long trips, shows, etc.
- Follow your veterinarian’s
recommendation for vaccination.
- If you have any concerns about your
horse, call your vet ASAP!
- Maintain a log of twice-daily
temperatures on horses that might be at risk.
- Temperatures >101 with possible
exposure to S equi infected horses should be isolated
from the general population and tested as described above.
- Isolate suspect horses ASAP.
Disinfect or dispose of equipment, personnel, tack, brushes,
etc. that have come into contact with these horses.
Thereafter, be sure to use separate equipment for each horse
and be sure handlers follow basic biosecurity protocols
(disposable boots, gloves, coveralls, etc) after handling
- Limit movement and exercise of all
horses and personnel on an affected farm.
- Maintain quarantine measures until
there is no further evidence of new, developing cases. At
this time, gradually remove quarantine restrictions as
recommended by your veterinarian.