“Strangles” is among the three most significant respiratory diseases of the horse. Until now it was not a great concern in our area. Unfortunately, there have been recent cases of this disease diagnosed in our area. Strangles is an upper respiratory infection caused by a highly contagious bacteria know as Streptococcus equi.

Transmission:  The disease is transmitted by contact with nasal discharge, oral secretions, and pus from infected horses on feeding utensils, buckets and other equipment. Typically outbreaks occur when large numbers of susceptible horses are brought together and exposed to a horse that is incubating or one that is still shedding the organism during the recovery phase. Occasionally, the recovery phase may be as long as several months. Carrier animals often go undetected and may shed intermittently for months thereby, introducing Streptococcus equi to premises previously free of the disease.

Signs of disease: The first signs of this disease can be seen 2-14 days after exposure to the bacteria. The disease is characterized by a sudden onset of fever (> 101 F or 38.5 C) and a clear bilateral nasal discharge that usually progresses to a thick white pus. Affected horses become depressed and eat and drink less as their throat becomes more inflamed and painful. The infection can eventually lead to audible respiratory distress (hence the name “Strangles”). Lymph nodes between the lower jaw bones and more typically around the throat-latch area can become enlarged, abscess and rupture. Complications of this disease can be severe and occur in about 20% of cases.  Death can occur in approximately 2% of cases, or rates can be as high as 10% in poorly managed herds.

Risk Factors: Strangles can affect horses of all ages, but it is most common in young horses. Cold wet weather, travel, and situations where many horses are put in close proximity to each other (ie. sales and competitions) also increase the risk of exposure to the disease. Premises where strangles has been a problem can harbor the infection for up to one year without proper disinfection.

Control: By vaccinating horses “at risk” of exposure and promptly isolating all new arrivals and observing them for signs of respiratory illness (2 weeks), you can minimize the chance that disease will be spread into your resident horse population.  In the event of an outbreak, affected horses should be isolated and persons working with these horses should stay clear of unaffected horses until clothing and footwear has been changed, and hands have been washed. Premises, pasture fences, stalls, buckets, halters etc. should be disinfected.

Vaccination: An intranasal vaccine is currently available for use in horses, foals and pregnant mares. As with most vaccines, protection is somewhat variable, depending on the individual immune response of each horse and previous exposure to this disease. Vaccine reactions and serious complications following vaccination can occur in rare instances, thus the decision to vaccinate your horse should be weighed against the risk of exposure to the disease. It is our recommendation that horses at risk of exposure be vaccinated. Due to the difficulty in administering intranasal vaccines and the small risk of anaphylactic reaction, veterinary administration is recommended. However, proper instruction can be given to clients at the time of the first vaccine should the client decide to administer the booster themselves. The vaccine can be purchased over-the-counter. This vaccine should not be administered at the same time as other vaccines since inadvertent contamination of injection sites may cause abscessation. The first year, two doses should be given 2 weeks apart. Thereafter, a once annual booster is all that is needed to maintain immunity. 

For Horses That Have Recovered From Strangles: a solid immunity is expected however, this immunity does not persist in about 30% of animals, which become susceptible again in a few months. Horses that have been previously exposed to the disease are at higher risk of suffering a reaction to the vaccine, and thus, your veterinarian should be consulted before vaccinating these horses. 

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