Strangles

WHAT IS IT?

“Strangles” is an infection caused by the bacteria Streptococcus equi, subspecies equi. It most often causes infection of the upper respiratory tract in horses, causing fever, nasal discharge, cough, and swelling and draining of the submandibular lymph nodes (located between the two sides of the lower jaw). This form of the disease is usually self-limiting (gets better without medications) and has a high recovery rate. Although it is very uncommon, strangles can also cause infection and abscessation of the lungs, abdomen, and internal organs. This internal form of strangles is known as “bastard strangles” and is much more deadly than the more common form of the disease.

HOW IS IT SPREAD?

Strangles is highly contagious and is spread through respiratory secretions from an infected horse, including nasal discharge, phlegm coughed up from the respiratory tract, and drainage from infected lymph nodes. The strangles bacteria can live in these secretions outside of the horse; this means it can live in the environment (feed buckets, walls, blankets, bits). This means that strangles can also survive on your clothing, on your hands, or in your hair and be transferred from one horse to another.

The strangles bacteria can live in the environment for up to several weeks, depending on its living conditions (temperature, humidity, location).

HOW CAN I PREVENT IT?

The best way to prevent strangles is to avoid exposure to infected horses and to have your horse vaccinated for strangles PRIOR to exposure to an infected horse. Although no vaccine guarantees complete immunity to disease in 100% of cases, it will protect many horses and will minimize the effects of disease in those who do contract the illness. Vaccinating your horse is the most effective way to protect him/her against strangles, other than avoiding exposure to infected horses when possible.

Please do NOT vaccinate your horse for strangles if it has recently been exposed to a strangles-infected horse. This will increase the risk that your horse may have an adverse reaction to the vaccine and/or get sick. Consult with your veterinarian to see if strangles vaccination is appropriate for your horse prior to administering any vaccinations.

HOW IS IT TREATED?

The vast majority of strangles cases are treated with supportive care, including hot-packing swollen lymph nodes and giving fever reducers and pain relievers as necessary. It is the minority of upper airway strangles cases that require antibiotics; horses that require antibiotics are usually more severely ill or have had significant throat swelling that has narrowed their airway. In most cases of upper airway strangles, antibiotic administration actually slows the process of recovery and may prevent the horse from developing an appropriate immune response to the bacteria.

Cases of bastard strangles are handled very differently from upper airway strangles. Horses with bastard strangles require antibiotic therapy and often require hospitalized care.

HOW DO I KNOW MY HORSE HAS RECOVERED FROM STRANGLES?

In cases of upper airway strangles, most horses have recovered (meaning they no longer feel or look ill) when their cough, nasal discharge, fever, and draining lymph nodes have gone away.

Horses who have had strangles but continue to have fever, weight loss, lethargy, or nasal or throat drainage should be evaluated by a veterinarian for persistent and potentially internal infection.

HOW LONG IS MY HORSE CONTAGIOUS TO OTHER HORSES?

Please note that just because your horse feels better does not mean that he or she is not contagious to other horses. Your horse may still be contagious to other horses, even though he or she appears to have recovered.

Horses who have had strangles may be contagious to other horses for a minimum of 3 weeks after all signs have resolved. Some horses are contagious for much longer (months). Although it is rare, it is possible for a horse to look well but to be chronically shedding the strangles bacteria to other horses over months or years. These horses are known as “silent shedders” and have a reservoir of strangles bacteria in their guttural pouches.

HOW DO I KNOW IF MY HORSE IS NO LONGER CONTAGIOUS TO OTHER HORSES?

In order to know if your horse is contagious to other horses, a diagnostic test must be performed to determine if your horse is shedding strangles bacteria from its nasal passages. These tests should be performed once horses stop showing clinical signs of strangles. Horses who are still symptomatic for the disease should be considered highly likely to still be infected and contagious.

There are two options for the test to see if your horse is contagious for strangles:

  1. A nasal swab is tested once-a-week for 3 weeks. If this test is negative on all 3 samples, your horse is considered to be clear of the strangles bacteria.
  2. A guttural pouch lavage is conducted and the fluid from this lavage is tested. If your horse is negative in this one sample, it is considered to be clear of the strangles bacteria. This guttural pouch lavage is done with endoscopic guidance.

Both of these tests can be conducted in a farm setting.

Without these diagnostics, it is not possible to know for sure if your horse has completely cleared the strangles bacteria from its upper respiratory tract or not.

HOW CAN I DECONTAMINATE/CLEAN MY BARN AFTER A STRANGLES OUTBREAK?

Once the horses in your barn are no longer symptomatic for strangles (no coughing, nasal discharge, fevers, or draining lymph nodes), it is possible to begin effectively decontaminating the environment from the strangles bacteria.

It is highly recommended that horses be tested for residual bacterial shedding, as described above, to be sure that horses are not only recovered but no longer contagious for strangles before thoroughly disinfecting the barn.

To disinfect contaminated objects or areas:

  1. Thoroughly scrub the object or area with soap and water until all organic debris has been removed. (Tide, the laundry detergent, works well here, but other options also exist.)
  2. Rinse the area of soap with water.
  3. If any dirt, debris, or doubt about the cleanliness of the object remains, scrub it again with soap and water and rinse.
  4. Next, apply a dilute bleach solution (1:9; bleach:water) to the area and let it sit for one hour. Please take great care not to get any bleach in your eyes, nose, mouth, or on your skin. Take protective measures such as safety goggles, face masks, gloves, and long-sleeved clothing. Contact a human physician or poison control if you have any concerns about your ability to handle bleach or if you feel you have been incorrectly exposed to this chemical in any way.
  5. After one hour, thoroughly rinse the area to which the bleach solution has been applied with water (wear protective gear as described). Thorough rinsing is especially important if the object or area in question may come into contact with horses’ eyes, nose, or mouth.
  6. Other less harsh chemicals/cleaners may be used on water buckets and feed buckets, but check that the solution is bactericidal for Streptococcus to be sure it is effective.

SHOULD A HORSE WHO HAS HAD STRANGLES BE VACCINATED FOR STRANGLES IN THE FUTURE?

In most cases, horses who have had strangles should not be vaccinated for strangles in the 4-5 years following infection. This is because most horses who have had strangles have a high strangles titer in the 5 years following infection and this titer is considered to be protective against the disease, making vaccination during this time unnecessary. Additionally, vaccination in the face of a high strangles-titer may generate an undesirable immune-mediated disease.

If your horse has had strangles, please be sure that he or she has a strangles titer (blood test) done prior to receiving strangles vaccines in the future to determine if it is safe for your horse to be strangles vaccinated. Please work with a veterinarian to determine if strangles vaccination is appropriate for your horse.

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