“My horse is currently living at a boarding facility and one of the other boarder’s horses was diagnosed with Strangles. Should I be worried about my horse?” -Sarah Peters

Dr. Denise A. Gorondy

YES, absolutely you should be worried about your horse!

Strangles is a highly contagious respiratory disease that affects horses. It is caused by the bacteria Strep equi that infects the upper respiratory tract of horses. Horses that are exposed to the bacteria will develop clinical signs within 3 – 14 days. Initial clinical signs are a high fever followed 2 – 3 days later by nasal discharge and subsequent lymph node swelling. The lymph nodes that are typically affected include the submandibular lymph nodes that are under the jaw and the retropharyngeal lymph nodes that are in the throat latch area. The infection can also be present in the guttural pouches. Depending on the degree of lymph node swelling, affected horses may have difficulty eating and drinking or breathing, hence the name Strangles. In most cases, Strangles is a disease that is self-limiting and the severity of the illness varies with the immune status and age of the horse. Immunologically naïve horses and young horses typically develop severe lymph node enlargement and abscessation resulting in the rupture and draining of lymph nodes. Older horses typically have a milder form of illness presenting with nasal discharge and less swelling and abscessation of the lymph nodes thus allowing for a more rapid disease resolution. Approximately 75% of horses that have been infected with Strangles develop a long lasting immunity to the disease.

Horse with retropharyngeal ymph node enlargement and abscessation

Horse with retropharyngeal lymph node enlargement and abscessation

Treatment for Strep equi includes supportive care in the form of anti-inflammatory medications to help control swelling of lymph nodes and fever, hot packing of swollen lymph nodes, and lancing of infected enlarged lymph nodes that are harboring purulent material. In the majority of cases, antibiotic therapy is contraindicated and can either slow down the resolution of the disease or lead to complications and worsening of the disease.

Surgical drainage of infected lymph node

Surgical drainage of infected lymph node

Horses that become infected with Strep equi will begin shedding the bacteria a few days after developing a fever and can continue to shed the bacteria for up to 4 weeks following resolution of clinical signs. A small percentage of horses become what are called chronic or silent carries that can intermittently shed the bacteria for months to years. Most of these horses have guttural pouch involvement in their infection. It is these silent carriers that typically cause recurring disease outbreaks when immunologically naïve animals are exposed to the bacteria.

Once a horse has been evaluated by a veterinarian and definitively diagnosed with Strangles, the entire farm should be quarantined. Testing for Strangles includes bacterial cultures from nasal swabs or washes or aspirated pus, PCR to look for the DNA of the Strep equi organism in cultures or washes, and serology to detect antibodies in the horse’s blood to Strep equi. In the state of Virginia, Strangles is considered a reportable disease and both the veterinarian and the laboratory performing sample testing are required to report the disease to the Virginia Department of Agriculture. The individual animal(s) affected by Strangles should be placed on strict isolation and handled following standard isolation protocols. In fact, Strangles is often spread to uninfected horses by farm employees that do not follow proper isolation technique and unknowingly transfer the bacteria either on themselves, on clothing, or on equipment from the sick horse to a healthy horse. Strep equi is a very hardy bacterium and can survive in the environment for lengthy periods of time. Bacteria lingering in the environment are another source of recurrent illnesses at certain farms.

Once all horses that were affected with Strangles have recovered, it is recommended that they have a series of 3 negative test results before coming off isolation and lifting the farm quarantine. Three tests are recommended as a way to identify horses that continue to intermittently shed the Strep equi bacteria.

There are 2 types of vaccines available for Strangles. One is administered intramuscularly and the second is administered intranasally. The Strangles vaccine should be considered a “risk based” vaccine and is not recommended for every horse. In fact, the vaccinations themselves can cause some of the complications that we see with the clinical disease. Vaccination in the face of an outbreak or following exposure is contraindicated.

So what should Sarah Peters do with her horse? For the time being, she needs to follow the farm quarantine protocols and absolutely stay clear of the isolated horses. Follow the advice of your veterinarian in regards to what is and isn’t safe for your horse. Once the farm quarantine is lifted and you are safe to resume travel with your horse, there are certain protocols to follow.

  • Avoid nose to nose contact with unknown horses. Do not share buckets, tack, or equipment with unknown horses.
  • Do not allow your horse to drink out of communal water troughs.
  • All new horses arriving to a facility should be quarantined for 3 weeks. Rectal temperatures should be taken daily and any horse with fever or nasal discharge needs to be evaluated by the veterinarian.

The best treatment for Strangles is to avoid it all together!