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365 Days in Horse Country – Strangles

Blog by Michael Stuart Webb | November 15th, 2013

365 Days in Horse Country – Strangles


This bacterial disease is called strangles because affected horses may develop a harsh cough or noisy breathing.  Caused by the streptococcus equi bacteria, it is a potentially deadly condition that attacks the lymph nodes, which are important to the healthy functioning of the immune system.

Strangles is an infectious disease that can be transmitted between horses directly or indirectly.  Shared drinking water is one source of transmission.  Anotehr is contact with stalls that have been contaminated.

Seven to twelve days after horses have been exposed to the bacteria, they start showing signs of the disease: fever, depression, and a runny nasal discharge that eventually thickens and usually becomes yellow.

Strangles is most common in younger horses between the ages of four months and five years, whose immune systems are not as developed as their older peers.  Older horse, who have been exposed to more “bugs” over their lives, are less likely to be affected.  Horses that have had strangles infections develop some immunity, but their resistance decreases with time.

As strangles progresses, the area of the throat where the lymph nodes are situated begins to swell, filling with pus.  Sometimes an abscess, known as a guttural pouch infection, forms and then breaks open, the thick pus oozing out.  If the abscess doesn’t rupture on its own, it may need to be lanced and drained by a veterinarian.

When a guttural pouch infection is suspected, the veterinarian will use an endoscope to take a look, obtain a culture via a swab, and flush the pouches with antibiotics.  Systemic antibiotics will also be administered to fight the infection.

The primary treatment for horses with strangles is rest in an isolated stall.  In the case of mild infections, the disease will simply run itss course.  Some veterinarians prescribe antibiotics to prevent an abscess from forming, but this is controversial because it can reduce the horse’s ability to build immunity against the disease, resulting in reinfection.  Other veterinarians prefer to give antibiotics only after an abscess has formed and ruptured.  Antibiotics, and sometimes a tracheostomy (an incision on the neck to create an airway so the horse can breathe), may be necessary in severe cases, in which the horse has a high fever and is in severe respiratory distress due to the formation of the abscess.

Most horses recover, but 15 to 20 percent develop secondary infections or complications.  These include laryngeal inflammation, paralysis, and chronic infection of the guttural pouches.  These horses become carriers of the disease.  Some carriers shed the streptococcus equi bacteria and may have recurrent episodes of coughing and nasal discharge.  Others don’t show signs of the disease but spread the bacteria to other horses.

Some horse may experience more serious complications of strangles than others.  Purpura hemorhagica is an immune-mediated problem that causes severe inflammation of the blood vessels, leading to swollen legs and hemorrhaging of the gums and mucous membranes.  It generally sets in three of four weeks after the initial infection.  Purpura hwmorrhagica is treated aggressively with antibiotics, steroids to dampen any immune over-response, diuretics, leg wraps if necessary, and hydrotherapy, usually in a hospital.

In “bastard” strangles, the streptococcus equi bacteria make their way to the lungs, liver, or kidneys, causing abscesses in those organs.  The abscesses may enlarge and rupture.  If this occurs, the resulting inflammation and infection can threaten the horse’s life.

Vaccines may not prevent the disease, but they can lessen its severity.  A horse who is already showing signs of the disease cannot be vaccinated, and vaccination should also be avoided in horses that have had strangles within the past year.  Giving a vaccine to these horses, who already have high numbers of antibodies to the disease, could cause them to develop purpura hemorrhagica.  Ask your veterinarian to take blood samples to check the titer, or level of antibodies, before giving a vaccine.

streptococcus equi bacteria can survive in freezing temperatures, in water, and on various surfaces, including wood and glass.  Even the cleanest, best-run facilities can have strangles outbreaks.  Nonetheless, practicing good hygiene around the barn and isolating all new horses that come to your property can help to prevent strangles.