Strangles Insidious, Infectious, & Inconvenient
Claudia True, DVM
Strangles -- a disease affecting the horse's lymph nodes -- can
not only make your horse ill, but is also highly contagious. If
it is diagnosed, your horse turns into a problem animal.
Strangles is a disease caused by the bacteria streptococcus equi.
The name comes from the fact that it enlarges the lymph nodes
between the jawbone, causing the horse to make strangled
The disease begins with high fever, depression and lack of
appetite. There is also a thin, watery nasal discharge that
quickly turns thick and yellow.
What's happening to your horse? The lymph nodes in the upper
respiratory tract become enlarged, the ones between the jawbones
being the most noticeable; they can abscess.
Although it usually isn't fatal in horses, it can be.
Horses of any age are susceptible, but those most disposed are
between one and five years. Susceptible horses usually acquire
the disease after being exposed to another horse that is shedding
the streptococcus equi bacteria that cause the illness. Often,
this is a new horse being introduced to the herd.
Although it may no longer be showing signs of the disease,
infected newcomers can spread it for about a month. (Shedding the
bacteria continues for up to one month after all clinical signs
are gone in 20 percent of horses.)
Horse-to-horse contact is the easiest way strangles infects, but
it can also be spread through contaminated equipment such as
buckets, stalls and tack. Fortunately, the bacteria can't exist
in the environment for long periods.
Once horses are exposed, they begin to show signs of the disease
in two to six days. Untreated horses will develop abscessed lymph
nodes which open and drain within one to two weeks after the
onset of the disease. Although most horses recover, about 10
percent of untreated horses die. Death most commonly occurs due
to a secondary infection causing pneumonia.
Occasionally, abscesses spread to other parts of the body -- the
lungs, liver or even the brain. This is known as "bastard
strangles." While uncommon, it is usually fatal.
Treatment depends on the stage of the disease.
To control strangles, if the health history of any horse new to
the stable is vague or unknown, it should be isolated, as much as
practical, for four or five weeks.
A veterinarian can take nasal swabs to confirm that the horse is
not shedding streptococcus equi. However, because the bacteria
can be shed sporadically, a total of three nasal swabs over a
period of seven days are required to assure that the horse is
Vaccinations are another useful control. Although current
vaccines are more effective and cause less reaction than those of
the past, they do not always prevent the disease. Still, the
severity of the disease is lessened if the horse has received the
One myth is that horses can get strangles from the vaccine. This
cannot happen since the vaccine is made from only parts of the
* (Please see Notation below)~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If strangles is suspected, notify your veterinarian to confirm
your suspicions. The sooner strangles is identified, the less
"down time" the whole barn will have to endure.
Horses with early signs of strangles should be treated with
appropriate antibiotics, which can prevent lymph node abscesses.
Outdated veterinary literature has warned against antibiotic
treatment at any stage of the disease because of the suspicion
that it could lead to bastard strangles. There is no evidence to
support this belief. Usually, horses treated at this stage fail
to recover only if antibiotics are not given in the correct
dosage or for enough days.
These animals still need to be isolated to stop further spread of
Once the lymph nodes become enlarged and abscessed, treatment
will only prolong the disease. It is better to allow the
abscessed lymph node to open and drain or to have your
veterinarian lance it. Treatment consists of flushing the
drainage site, keeping the area clean and strict isolation of the
What to do if the horse you were stabled next to at the show had
Since horses usually show signs two to six days after exposure,
it makes sense to treat the horse with antibiotics for at least
six days after exposure. However, if your horse remains in a barn
where strangles is present, this will be of little use.
* Editors Note:
After reading the above information, one of our readers
wrote in with the following story:
"Just read the information on your site about strangles. wanted
to let you know that the myth concerning the vaccine is incorrect.
The nasal vaccine can and does cause strangles."
"I have a filly here right now with a bad case of strangles
that has been cultured and proven to be caused by the
vaccine strain. The same thing has happened to other weanlings.
Fort Dodge is currently doing a case study on my filly, but
wanted to let you know so as not to spread false information.
No weanling under the age of 9 months should have this
vaccine as well as it being imperative that it be given only
under proper circumstances and not in conjunction with
any other vaccines."