Caused by the bacterium Streptococcus equi, this highly contagious disease is most common and severe in young horses.

One beautiful spring morning, you are milling around  in the barn after the morning feeding trying to decide how to spend the rest of the day. Then you notice that one of your horses just isn’t quite right today. The mare is not typically an aggressive eater, but today she really is not interested in her morning grain ration at all. On closer inspection, you notice that she feels warm. A quick check with a thermometer reveals a temperature of 103.5 degrees Fahrenheit–significantly above her normal 100.4 degrees Fahrenheit. You also note that there is a cloudy nasal discharge from both nostrils, and as you are stroking her head, you notice several small “lumps” in front of the throat latch area that she resents you touching.

After a visit and consultation with your veterinarian, your fears about “strangles” are confirmed, and within several days, two more horses in the barn are showing similar signs.This scenario is a typical textbook description of a strangles outbreak, a problem with which many horse owners are all too familiar.”Strangles” is a disease caused by the bacterium Streptococcus equi, a Gram positive (stains purple with the special Gram stain) organism that is considered to be an “obligate” parasite of the equine species.

The nature of a species of bacteria that is considered to be an obligate parasite is that it does not survive well outside the horse’s body. But, as we will discuss later in this article, it survives well enough and long enough to be transmitted from horse to horse via nasal secretions and pus from draining abscesses