Mention the word "strangles" to a horse person and they may cringe. The disease is so dreaded because once it is diagnosed on a farm, the you-know-what really hits the fan.
Strangles is caused by infection with Streptococcus equi bacteria. Horses are exposed to the bacteria either through contact with an infected horse or through contaminated objects (e.g., water buckets, grooming supplies, etc.). The bacteria gain access to the horse’s body through the nose or mouth and then travel to the surrounding lymph nodes. Those lymph nodes become swollen and painful due to abscess formation and typically rupture and drain pus either through the skin or into the throat and nasal passages.
Typical symptoms of strangles include
swollen lymph nodes around the head and neck
pus draining out of the nose or through skin around the head and neck
loss of appetite
The phrase "bastard strangles" is used to describe a rare form of the disease where other lymph nodes (often those deep within the chest or abdomen) are affected.
The terminology of this disease is pretty graphic, isn’t it? "Strangles" was used to describe the condition because on occasion the lymph nodes around the throat would get large enough to suffocate an infected horse.
Strangles can often be diagnosed based on a horse’s clinical signs, but confirmatory tests that identify S. equi as the cause are readily available. Treatment is basically symptomatic. Warm compresses may be applied to abscesses to encourage them to mature to the point where they can be easily lanced and drained or rupture on their own. Non-steroidal anti-inflammatories are often prescribed to reduce fever and discomfort, which will usually get affected horses eating again. Antibiotics are not typically used except when the disease is diagnosed very early in its course or if complications arise, since they may increase the risk that "bastard strangles" will develop.
Another potential complication of strangles is a condition called "purpura hemorrhagica," which is a relatively rare but severe immune-mediated disorder that can arise several weeks after a horse develops strangles (or after vaccination). Horses with purpura hemorrhagica develop bruising and swelling over large parts of the body.
Despite all the dire-sounding language and occasionally severe complications associated with the strangles, most horses recover uneventfully, which begs the question, "Why do horse people freak out at the mere mention of the disease?" The answer: it is extremely contagious, and once it is diagnosed on a farm, the whole premises should be strictly quarantined, the horses divided into "clean" and "dirty" herds to prevent spread of disease at that location, rigorous isolation and disinfection protocols put into place, and in some states, the state veterinarian must be notified. Having a case of strangles on a farm is a pain in the rear for everyone involved.
Preventive vaccines for strangles are recommended for horses that have significant contact with other horses, but the protection they offer is not complete (especially with the “killed” vaccine) and their use is sometimes associated with undesirable side-effects (especially with the attenuated, live intranasal vaccine).
So that’s strangles in a nutshell. For more information, check out this article on the American Association of Equine Practitioners website.