Equine Strangles - Steinbeck Country Equine Clinic

Your Horse's Health
Veterinary Medicine with
Nora Grenager, VMD
Published in Bay Area Equestrian Network September 2006.
Equine Strangles
Strangles is a highly contagious respiratory disease of horses caused by the
bacteria Streptococcus equi subspecies equi. The disease was initially given this name
because it can cause abscesses of the lymph nodes in the throatlatch region, which if
severely enlarged can compress the airway and suffocate the horse.
The strangles bacteria enter through
the nose or mouth and travel through the
tonsillar area to the submandibular (under the
jaw) and retropharyngeal (at the throatlatch)
lymph nodes. Once in the lymph nodes, the
bacteria begin to replicate as the body’s
immune system tries to fight them off. Horses
begin to shed infectious bacteria from their
noses 2-3 days after the onset of fever and can
shed for 2-3 weeks. Transmission can be
direct (horse-to-horse nose contact) or indirect
(shared housing, shared water or feed
Abscessed submandibular lymph nodes
containers, shared equipment, and people).
Infected horses typically get a fever 314 days after exposure to the bacteria. This is followed by a large amount of
mucopurulent (yellow/white snot) nasal discharge and painful swelling of the
submandibular and retropharyngeal lymph nodes. Affected horses may be depressed,
lethargic, have a sore throat, and be reluctant to eat. The lymph nodes will enlarge and
eventually rupture, draining creamy yellowwhite pus. Horses typically feel better once the
lymph nodes have ruptured.
Culture of nasal swabs or abscess
material is the best way to diagnose strangles.
Cultures are diagnostic approximately 70% of
the time. Another test called the polymerase
chain reaction (PCR) is rapid and very sensitive
at detecting bacteria, but cannot distinguish
between live and dead bacteria. Serology
(blood samples to detect the horse’s antibody
levels to the bacteria) can be helpful but often
necessitates two samples taken two weeks apart
to confirm current infection. Multiple horses on
Nasal discharge in horse with strangles
a property with the typical clinical signs is also
suggestive of a strangles outbreak and should be treated as such.
If strangles is suspected on a farm, all horses at that location should be divided
into three groups: infected horses with clinical signs, horses that have no clinical signs
but may have been exposed to the bacteria or to a sick horse, and horses without clinical
signs who have not been exposed. Rectal temperature should be taken daily of all horses
on the property (or at least those that have been exposed).
Horses that have clinical signs of enlarged lymph nodes should generally be
treated with supportive care aimed at enhancing lymph node abscess maturation and
drainage. Antibiotics are not typically recommended because they just delay, not
prevent, the abscess maturation. It is best to use a hot pack or topical drawing agent to
promote maturation of the abscess until it opens and drains on its own. Sometimes if the
abscess is mature (has a soft center), drainage can be surgically performed by a
veterinarian. Once the abscess is open, it should be flushed once or twice daily with a
dilute antiseptic solution until there is no more drainage. Horses may be given antiinflammtory medications such as Banamine or bute to help reduce fever and any pain.
Horses without clinical signs that develop a fever (if their temperature has been
monitored daily) may be given antibiotics for 5-10 days (veterinarian-dependent) to
prevent lymph node abscessation. They can also be treated with anti-inflammatories like
the horses in the previous group. These horses will remain susceptible to reinfection after
the antibiotic therapy is discontinued.
If Strangles is suspected or diagnosed on a farm, a plan should immediately be
implemented to prevent spread of infection. Every situation is unique and requires the
veterinarian and barn manager/owners to develop the best quarantine and treatment plan
for that location. Movement of all horses on and off the property should be stopped.
Horses should be segregated according to the three previously mentioned categories
(sick, exposed but not sick, not exposed and not sick) with no mixing of equipment
(especially water troughs) or people between the three groups. All
horses should have their rectal temperatures taken once daily to
identify any new infections as early as possible. Ideally recovering
horses should have 3 negative cultures or PCR samples prior to
Culturette
being considered noninfectious but this is often not economically
practical. It is not entirely clear how long the bacteria can live in the environment, but
most veterinarians recommend quarantining infected pastures or stalls for 4 weeks.
Equipment can be cleaned with a dilute bleach (1:10) solution.
Up to 10% of horses can become carriers of Strangles and shed infectious
organisms, even without clinical signs. Most often these horses are harboring the Strep.
equi bacteria in their guttural pouches. This infection can be a result of a retropharyngeal
lymph node abscessation into the guttural pouch. It is easiest to diagnose a guttural
pouch infection by endoscopically visualizing the guttural pouches. Your veterinarian
may be able to perform endoscopy at the farm, but often it will need to be done at a
referral facility. It is also possible to lavage the guttural pouch and collect the fluid for
culture or PCR. This is a useful way to monitor a horse with a diagnosed guttural pouch
infection.
Preventing strangles is obviously preferable to dealing with an outbreak but it can
be difficult. When possible, a horse being brought to a new location should be isolated
for 3 weeks to evaluate for any clinical signs. This is sometimes not feasible given that
horses often mingle with other horses at events.
Horses that have had the disease usually develop a good natural immunity for up
to 5 years. Vaccination and good biosecurity are ways to prevent outbreaks. Two basic
types of vaccine exist; both require a booster at 2-4 weeks, and both should be given once
a year. There are an intramuscular vaccine and an intranasal vaccine. The intranasal
vaccine is generally associated with better immunity and less adverse side effects. It is
best to talk with your veterinarian about whether your horse should be vaccinated, and
with which vaccine. As with most diseases, vaccination decreases the severity and
duration of clinical signs, but does not completely prevent the disease. Vaccine reactions
are rare but include purpura hemorrhagica and guttural pouch empyema (discussed later).
Some horses may get a mild strain of the disease with fever and lethargy following
vaccination. The vaccine manufacturers recommend not vaccinating horses in the face of
an outbreak unless there has been no possible exposure. This, however, should be
tailored to each specific situation.
Most horses that get strangles need rest and supportive therapy but recover from
the disease without complication. However up to 20% of horses can have complications
such as guttural pouch empyema (infection), “bastard strangles,” or purpura
hemorrhagica.
Guttural pouch empyema can be treated with an indwelling catheter lavage
system, guttural pouch antibiotics, and systemic antibiotics. Occasionally the pus can
become dried out and form little concretions called “chondroids,” which may need to be
removed surgically. Horses should be quarantined while being treated for guttural pouch
empyema. The only way to definitively prove that the infection is cleared is three
negative guttural pouch cultures at weekly intervals.
Normal guttural pouch
Guttural pouch with chondroids
and indwelling catheter.
Bastard strangles is when an abscess forms in a lymph node at a distant site such
as the lung, abdomen, liver, spleen, kidneys, or brain. These infections have varying
clinical signs depending on the location, and can be difficult to diagnose. There is a
blood test (for “SeM-specific antibody titer”) that can be useful. These infections are
hard to treat and require long-term antibiotics and sometimes even surgery.
Purpura hemorrhagica is an immune-mediated vasculitis, which means the horse’s
blood vessels are compromised by immune complexes secondary to the bacteria. The
compromised blood vessels lead to edema (swelling of the limbs and belly), petechiation
of the mucous membranes (spotty gums), and fever all of variable severity. This is
uncommon but can be a very serious complication requiring intensive treatment with a
guarded prognosis.
Strangles is considered one of the three most significant respiratory diseases of
horses. Because it is so highly contagious, and horses are a very mobile population,
achieving prevention and control can be difficult. It is important to be aware of the
typical clinical signs and discuss vaccination of horses at risk with your veterinarian.
Nora Grenager, VMD
* Grew up on a small farm in central Pennsylvania
* 2000—Graduated magna cum laude with a B.A. in biology from Amherst College in
Massachusetts
* 2005—Graduated magna cum laude from the University of Pennsylvania School of
Veterinary Medicine
* 2005—Joined Steinbeck Country Equine Clinic and is currently finishing
certification from the American College of Veterinary Internal Medicine
* Volunteer with Rural Area Veterinary Services
* House of Delegates Representative for the Monterey Bay to the California Veterinary
Medical Board
* Committee Member of the International Conference on Laminitis and Diseases of the
Foot
* Organizing Committee Member of Laminitis West Conference
* Member of the Monterey County Large Animal Evacuation Group
* Publications: 1. Orsini JA, Grenager N, Carr J, Benner P. "What is your diagnosis?
Diagnosis: midsagittal nondisplaced Salter-Harris type III fracture of the proximal
phalanx of the right hind limb." J Am Vet Med Assoc. 2006 Feb 1;228(3):353-4.
2. Rabuffo TS, Hackett ES, Grenager N, Boston R, Orsini JA. "Prevalence of Gastric
Ulcerations in Horses with Colic."
Journal of Equine Veterinary Science. Jun 2009: 29 (6):540-546.
3. Orsini JA, Hackett ES, Grenager N. "The Effect of Exercise on Equine Gastric
Ulcer Syndrome in the Thoroughbred and Standardbred Athlete." Journal of Equine
Veterinary Science. Mar 2009; 29(3):167-171