Quarantine the horse immediately and closely monitor all exposed horses with twice-daily evaluation of temperature. This presentation is consistent with strangles, a highly contagious respiratory disease. You can confirm the diagnosis with PCR/culture of a nasal swab or swab of drainage from an abscessed lymph node.
Strangles (Streptococcus equi sbsp. equi infection) infects the lymph nodes of the upper respiratory tract and the ensuing lymphadenopathy can «strangle» the horse as seen in this case. It first causes a fever, followed 24-28 hours later by mucopurulent nasal discharge and then lymph node enlargement and abscessation.
As the disease progresses, the affected lymph nodes enlarge and eventually rupture and drain purulent exudate. If the retropharyngeal lymph nodes are affected, they can rupture and drain into the guttural pouches, setting up a carrier state.
Most cases of strangles respond to supportive care – judicious use of NSAIDs, facilitating abscesses maturation, flushing the abscesses once open/draining. Use of antibiotics depends on severity of clinical signs and the number/ages of horses affected.
Antibiotic therapy is controversial – can delay maturation of abscesses and prevent development of protective immunity.
Antibiotics ARE routinely used for horses with metastatic internal abscesses (i.e., bastard strangles), guttural pouch empyema (infection), or those with complications (tracheotomy, severe/prolonged illness).
A horse recovered from strangles should be proven negative before returning to the herd because a carrier state can develop in the guttural pouch. Negative means three negative PCRs or cultures on nasopharyngeal washes or one negative PCR/culture from the guttural pouches (requires sedation and more expertise).
Check out the 2018 ACVIM Consensus Statement on Strep. equi equi infections to answer all your strangles questions in horses.
Image courtesy of WD Wilson/Stephanie Brault.
