Strangles carriers – an inconvenient truth
Once infected, the majority of animals recover from the disease and eliminate S. equi over a 4–6 week period. However, up to 10% of affected animals continue to shed S. equi intermittently for prolonged periods after clinical signs have resolved.
This carrier state is probably caused by incomplete drainage of pus from the guttural pouches and/or sinuses following rupture of abscesses formed in the retropharyngeal lymph nodes at the back of the horse’s head. Over time the pus dries and with the movement of the horse’s head forms discrete bodies called chondroids that can remain in the guttural pouch for several years. It is becoming increasingly recognized that sub-clinical persistent carriage of S. equi is fundamental to the global prevalence of this infection.
Endoscope image of a retropharngeal abscess
rupturing into the guttural pouch.
Endoscopy image of a chondroid in the guttural pouch.
Control of strangles after outbreaks traditionally relies on the collection of three consecutive negative nasopharyngeal swabs at weekly intervals. However, carriers shed S. equi intermittently and may be culture negative over several weeks or even months and so the culture of wash samples collected from the guttural pouch is now considered the gold standard for carrier detection.
Once identified carriers can usually be treated very successfully through the removal of chondroids using a basket snare and subsequently instilling a penicillin gel into the guttural pouch to kill any remaining bacteria. For further details of treatment and quarantine procedures follow this link to the STEPS guidelines
Performing a guttural pouch wash.
‘Snaring’ a chondroid to treat a strangles carrier.
