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Streptococcus equi


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Strangles and vaccination

What is Strangles?

Strangles is a highly contagious respiratory disease in horses worldwide. It is caused by the bacterium Streptococcus equi subspecies equi and is characterised by fever and abscessation of the lymph nodes of the head and neck. The disease can affect any age, sex or breed of horse and is endemic in the horse population, meaning it is always circulating at any given time.

There are approximately 300 outbreaks of strangles diagnosed each year in the UK, and 100 per year in Sweden, with a similarly high prevalence of the disease believed to occur throughout Europe. However, the true prevalence of strangles outbreaks may be even higher as not all cases are reported to veterinarians, or confirmed through laboratory diagnosis.

Why vaccinate against Strangles?

Vaccination provides the best possible protection against Strangles. As an outbreak of Strangles has both welfare and economic consequences to a herd, control of the disease is an important aspect of stable management. We recommend that all horses in a stable yard be vaccinated to provide the best protection against the disease.

Does the vaccine provide 100% protection?

A regular program of vaccination for all horses will usually control or very markedly reduce the incidence and severity of strangles. However the vaccine is not an absolute preventative. The manufacturer claims the following benefits from vaccination "Reduction of body temperature increase, coughing, inappetence, difficulty swallowing, and changes in demeanour in the acute stage of infection with Streptococcus equi. Reduction of number of abscesses within submandibular and retropharyngeal lymph nodes." Vaccination has good benefits and is the best protection possible. However vaccination does not replace the need for good stable management and procedures for introduction of new horses to a yard.

About the vaccine

The original (in the lip) vaccine has now been discontinued by the manufacturer and is no longer available. Fortunately, a different manufacturer has developed a different vaccine which is now available.

Vaccination Protocol - "Official Version"

The current vaccine is given by intramuscular injection. Two doses are given 4 weeks apart. After the initial course, the duration of immunity is 2 months. Following this, revaccination with another initial course is required. This protocol may be useful in the face of an outbreak but isn't useful for providing long term protection.

Vaccination Protocol - "Unofficial Version"

The vaccine manufacturers have good data from their clinical trials to support a more useful way of using the vaccine with a protocol much more similar to a typical vaccination schedule. However, as this is not approved by the regulatory authorities, you will need to speak to your vet directly about and take their advice regarding this "off-licence" use of the vaccine. We expect that most people will use the vaccine this way.


What is the minimum age for vaccination?

Horses can be vaccinated from 5 months old.

Can the vaccine be used in the face of an outbreak?

Only healthy horses should be vaccinated. Even vaccinated horses can become infected and then infect others. The vaccine will reduce the severity of the disease and so is useful in the face of an outbreak, but the vaccine alone will not stop the disease spreading.

My horse is the only one on the yard to be vaccinated, is there any benefit in continuing?

Yes, efficacy has been demonstrated for the individual horse to reduce clinical signs of disease in the acute stage of the infection.

Can a vaccinated horse become a carrier of the vaccinal strain?

No, the vaccine does not contain live Strep. equi or Strep. equi DNA. Therefore, horses that have been vaccinated will not test positive for strangles in diagnostic culture or PCR tests, unless they have been recently infected with Strep. equi.

In addition, the vaccine does not contain the proteins used in the strangles blood tests, so vaccinated horses will not test seropositive unless they have been exposed to Strep. equi.


Can my horse have his vaccination while he is on antibiotics?

No. Only healthy horses should be vaccinated.

Can pregnant or lactating mares be vaccinated?

The vaccine has not been tested in pregnant or lactating mares, therefore it is not recommended during pregnancy or vaccination.

Are there any side-effects?

Yes, the following side effects are seen quite commonly:

  • An increase in body temperature lasting 1-5 days.
  • A swelling (possibly hot and sore) at the vaccination site.
  • Runny eyes lasting for1-5 days
  • Loss of appetite for up to 1 day

and, like all vaccines, more serious complications such as anaphylaxis are possible but are very rare.