Declaring A Farm "Strangles-Free"
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During a strangles outbreak, people often ask how (and when) they can say their farm is "strangles-free." They usually don't like the answer. Declaring a facility to be free of strangles, a highly contagious disease caused by the bacterium Streptococcus equi, is not cheap, easy or quick. It is, however, important.
A major source of the strangles bacterium is horses that have been infected but either didn't get sick or have recovered, yet are still shedding S. equi in their nasal secretions. In some horses, S. equi can persist for long periods of time (i.e. months) in their nasopharynx (throat area) or guttural pouches. Identification of these carriers is crucial for strangles control and must be done to have confidence that strangles has really been eradicated from a farm.
Identification of carriers involves taking samples from the nasopharynx to test for the bacterium. Nasopharyngeal washes are preferred but nasopharyngeal swabs (note: this is different from a nasal swab) are also acceptable. These should be collected by a veterinarian. They can be tested for S. equi by culture or PCR (a molecular test), or both. Any positive horses need to be investigated further, including endoscopy and culture of the guttural pouches.
Three negative samples from the nasopharynx and/or guttural pouches, collected weekly, are required to declare a horse free of strangles. If a positive horse is identified during the process, the clock starts again on its testing, plus all other horses with which it has had contact. Even though a horse may have had three negative samples, if it has been in contact with a positive horse, you have to assume there's a chance it was infected after testing started, so you need three more samples after its last contact with any positive horse.
While this process is not cheap, easy or quick, it is strongly recommended.
At the same time, it's also a good idea to review why the strangles outbreak occurred and how it can be prevented in the future. This is a step that's often overlooked.
More information about strangles can be found on the equIDblog Resources page and in our archives.
Image: A horse with draining tracts from classic strangles abscesses between the lower jaw bones
