our expertise: VET COLUMN
Get A Grip On
“Strangles”
BY TOM HUTCHINS, DVM, DABVP
Dr. Tom Hutchins
S
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trangles is caused by the organism
Streptococcus equi subspecies equi (S. equi).
The infection is an acute respiratory infection
characterized by fever, lethargy, nasal discharge,
respiratory noise and regional lymph node
abscessation. Some horses may exhibit signs of
difficulty eating or swallowing and coughing.
S. equi is inhaled or ingested after direct
contact with purulent discharge from infected
horses or contaminated equipment. Eventually
it spreads to the regional lymph nodes, such as
the submandibular or the retropharyngeal lymph
nodes.
The submandibular lymph nodes are between
the jaw bones and just in front of the throat latch.
This is the common site that many people notice
enlargement. The retropharyngeal lymph nodes
lie just above and behind the larynx and often
times swelling is not noted until they become large
enough to see swelling behind the jaw bones and
above the throat latch.
Fever occurs 3-14 days after exposure. Nasal
shedding of the organism occurs 2-3 days after the
onset of fever, persisting for 2-3 weeks. Seventy-
five percent of horses develop immunity after
natural infection that can last up to five years.
Older horses can develop a mild form of strangles.
Disease occurs sporadically on farms, but once
present, infection rates will depend on the age of
the animals (ranging from 32% to 100%). Death
rates are generally very low in uncomplicated
cases (<2%) but higher for cases of bastard
strangles where the infection has spread to other
locations throughout the body.
Definitive diagnosis via cultures from nasal
swabs, nasal washes, guttural pouch washes, or
pus aspirated from abscesses is the gold standard.
Diagnostic imaging is typically not performed
in uncomplicated cases. Swellings of the upper
respiratory tract can obstruct the airway which
can be seen on radiographs. Abscesses in the
abdomen may be detected with ultrasound
depending on the location of the mass. Endoscopy
and radiographs of the guttural pouches aid in the
diagnosis.
A dry and isolated stall, rest, and soft, moist
palatable food may be all that are necessary
while letting the disease run its course. Early
phase of the fever and depression can be treated
with antibiotics but this will prevent protective
immunity in the future. It can prevent the
formation of abscessation. Antibiotic treatment
is controversial because it has been argued that
this will make the animal more susceptible to
infection and further abscess formation in other
lymph nodes. Horses with lymph node abscesses
can benefit from hot-packing or topical treatment
with ichthammol to encourage maturation of the
abscess and drainage, followed by flushing with
an antiseptic solution once opened. Judicious
use of anti-inflammatories can decrease swelling
and promote eating. Horses with complications