How often has a horse-show weekend dawned, and all the planning and excitement fizzles on the mere rumor that a case of Strangles has been detected at the show grounds?
What is this dreaded contagion that can cause even the most diehard competitor to withdraw from a show, or send any barn to start serious cleanup efforts and quarantine restrictions?
In this week’s Veterinary Answers Q&A, Dr. Kelly Carlson, DVM, DACVIM, of Rood & Riddle Equine Hospital talks about disease, and how it is spread.
Q: What is Strangles? And, is there a time of year, or conditions, that make the disease more prevalent?
Strangles is the common name for a bacterial infection (typically of the respiratory tract) caused by Streptococcus equi subspecies equi. This bacterial name is frequently shortened to Streptococcus equi, Strep equi or S equi. Strangles may occur in any age horse, but is most common in horses 1-5 years of age. Therefore, conditions that result in co-mingling of young horses (sales, horse shows, race tracks, etc.) have an increased risk of Strangles.
Q: How is the disease spread? And, is it contagious to people?
S equi bacteria are shed in the horse’s nasal secretions. Nasal shedding begins 2-3 days after the onset of fever and typically lasts for 2-3 weeks. Horses that have S equi infection within the guttural pouches may shed for long periods of time (months to years), acting as a source of infection to naïve populations.
Strangles may be spread via direct transmission (nose-to-nose contact) or indirect transmission (nasal secretions on buckets, brushes, twitches, tack, clothing, etc.). The risk of transmission to people is very low, but there are rare reports of S equi causing bacteremia and meningitis in people. Individuals who are immunocompromised should be careful handling any sick horse.
Q: What are the initial symptoms of the disease, and how do they progress in a typical case?
The first symptom of Strangles is generally a fever, followed by nasal discharge and swelling (lymphadenopathy) of the submandibular and retropharyngeal lymph nodes.
These lymph nodes are found under the jaw and deep within the throatlatch region of the horse. In mild cases, the lymph node swelling may resolve with time. In more severe cases, the lymph node swelling may progress to abscess formation, which may then require drainage for resolution.
The lymph nodes in the retropharyngeal region may become large enough to compress the upper airway, leading to respiratory distress.
The name Strangles came from horses that had difficulty breathing due to the swollen lymph nodes. In atypical cases, S equi can infect lymph nodes and organs in other parts of the body, resulting in various clinical signs, depending on the location of the abscess. This condition is sometimes referred to as bastard strangles.
Q: If a horse is suspected of carrying the disease, what course of action should the owner take?
If an owner suspects that their horse has Strangles, they should contact their veterinarian for a thorough physical exam. Their veterinarian may elect to pursue diagnostic testing or recommend treatment based on the individual case. Owners and barn managers should work with their veterinarian to determine appropriate isolation and biosecurity measures to help prevent spread to other horses.