Download Strangles Facts and Fictions Because of the recent outbreaks of

Strangles Facts and Fictions
Because of the recent outbreaks of Strangles in Central Vermont (in my practice in the past year I have
conclusively diagnosed 2 horses in Northfield, 1 horse in Duxbury, and 2 horses in Barre/Plainfield) I
want to take a moment to go over how you can protect your horses from this highly infectious disease.
Strangles is a bacterial infection that causes the lymph nodes around the head and neck to become swollen
and filled with pus and then abscess. There is usually quite a bit of nasal discharge. Not all Strangles
presents this way, though, and sometimes all you see is a fever and a tiny amount of nasal discharge.
While the bacteria can exist in the environment for up to 4 weeks (possibly slightly more given the right
conditions) it is maintained in horse populations by asymptomatic carriers. A random sampling of horses
will show that as many as 3-5% of the horse population carries the bacteria in their guttural pouches and
sheds the bacteria intermittently. On farms where Strangles occurs intermittently, as many as 40% of the
horses may be carriers.40%!
The time between exposure and the first fevers or signs of disease is 3-14 days. That means that once
your horse is exposed he should show signs of illness within 14 days if he is going to become sick. It is
thought to be possible for horses who never become ill to become carriers, but certainly any horse who
develops the disease can become a carrier. Treatment of carriers is time-consuming and costly and
involves flushing of the guttural pouches with penicillin repeatedly.
The only way to protect your own horses is to vaccinate him against Strangles. The vaccine does have
some risks, but the intranasal vaccine has many fewer than the injectable and is the only vaccine I use. It
is called Pinnacle. You need to be careful vaccinating horses who have been exposed to the bacteria as
exposed horses are more likely to have severe vaccine reactions. Even if you do vaccinate your own
horse, he can still develop the disease-- it is usually just a more mild case. Anecdotally, it seems that
about 75% of horses who are vaccinated with good technique will have protection that prevents the
disease. Maybe 15% will get a mild case of Strangles. Then 5-10% will get the full-blown disease.
Horses also can develop a strangles-like disease from the vaccine itself. When this happens, the vaccine
company will usually pay for the PCR test to prove that it is the vaccine and not Strangles causing lymph
node enlargement and/or abscessation so that you do not need to isolate your horse and test him to make
sure he is not a carrier. If your horse has a reaction to the vaccine that looks like Strangles but is not, he is
not infectious to other horses and is very likely to have excellent protection against Strangles in the future
from that strong vaccine response!
If you have a horse who comes into contact with a lot of other horses (remember as many as 1 in 20
completely healthy horses shed Strep equi intermittently) then please discuss vaccination against
Strangles with your vet. Also use good hygiene when out and about with your horse: no nose to nose
contact with other horses. Use your own water buckets. Don’t share bits without disinfecting first. At
very busy show facilities, using disinfectant on the stall fronts where your horse is most likely to hang out
might help reduce transmission. Most importantly, all horses at shows should have rectal temps taken
and recorded twice daily! Don’t let your competitors make a joke of this!
If you have had a horse with Strangles or work with a farm where the disease has been diagnosed,
hygiene and prevention are paramount. Ideally all sick horses should be isolated. Horses exposed but not
sick should be in a second group. Unexposed horses in a third. Three pharyngeal cultures/PCR tests
should be taken and found negative before reintroducing an exposed horse into the herd of unexposed,
healthy animals. On farms where Strangles is actively occurring, all animals should have a rectal temp
taken and recorded twice daily. Your vet should be called for any animal with a rectal temp >101.5F.
I know that Strangles is a nightmare for horse and barn owners and I wish that I could make it easier for
you, but sadly quarantine, hygiene, careful monitoring (temperature taking) and testing are what is
required to really get rid of this amazingly infectious disease from any farm.
For more information on quarantine and vaccine, see the AAEP pages on Strangles.