“Doc – My yearlings have had strangles for two months. I can't get them over it!”
© A.J. Neumann, D.V.M.
published in The Draft Horse Journal, Spring 2004

Of all the equine diseases which veterinarians and horse owners have to deal with, strangles is probably the most common, the most difficult to treat and the most costly to the owner or producer. It is not uncommon to answer the phone and the party calling will tell you he or she is having a problem with strangles, much like the title of this paper.

Strangles is an infectious disease of horses, asses and their hybrids–the mule and hinny. It frequently occurs in young animals but may infect a 3-, 4-, or 5-year-old. An animal which has had one attack, is generally immune from that time on for life.

Strangles was one of the first equine diseases to be recognized. Records of its presence have been left by almost every civilization where the horse was used and written records were kept for future generations. The Greeks, Romans and the great Khans of Asia knew about it and recorded its deprivations on their horses.

In 1664, a writer named Solleysel, gave an account of this disease and makes a point that it had been known for a very long time. In 1790, a scientist named Lafosse proved experimentally that the condition was contagious among horses. Rivolta, in 1873, found chains of micrococci in the pus from abscesses, but it wasn’t until 1887 that a scientist named Barvchello definitely described the cause of strangles to be a micrococus, which he named Adenitis equi. In 1888, work was being done on this organism by many scientists and the micrococcus was named Streptococcus equi and is considered today to be the causative agent of strangles. In the same year a researcher, Schütz, was able to reproduce the disease in healthy horses using pure cultures of streptococcus equi.

In nature, the organism is transmitted from one horse to another by the purulent discharges of the infected animals. Infection will be acquired by contact with the nasal discharges and the pus from abscesses as they contaminate feed, water or just plain objects in the animals’ surroundings. It has been found that contaminated premises may remain a source of infection for a year or more even though they are not occupied by horses, mules or asses.

I believe that some horses can be carriers of this disease. I have known of situations where susceptible young horses were brought onto a farm where other adult animals were kept without any signs of strangles for years and within a week or 10 days later the young, susceptible stock would come down with the disease. Further checking into the origin of the sick stock revealed no infection on the premises of origination and the animals had been transported in stock trailers which had never been used to haul horses or mules. In addition, the transported stock had not been unloaded, fed or watered, but had only been moved a relative short distance to their new home where they were exposed to older horses.

Recently it was thought that a virus played a role in the disease, but this is not the case. The streptococcus is the sole cause in the development of strangles.

The incubation period of strangles is from three to eight days. The onset and course of the disease has been well documented. If a virulent culture of streptococcus equi is sprayed into the nostrils of a susceptible horse, and the animal is closely watched, the first symptom of the disease which is failure to drink will appear within the three-to-eight day time period. At that point the animal’s temperature will be elevated at 104 to 106 degrees F. A nasal discharge will be present as the temperature elevates. It starts as a clear mucoid fluid which quickly turns into a thick, greenish yellow discharge.

At this stage of the game the ball is rolling downhill and the disease quickly picks up speed because the little streps are setting up housekeeping in the tissues of the pharynx. As this happens, the victim will begin to show signs of severe pain in the throat region. We become aware of this fact because the animal will be reluctant to swallow and it will carry its head in a position whereby the nose is elevated and points straight forward. It also will not want to bend the throat region in any direction.

At the same time that we notice the elevated temperature, the nasal drainage and the swollen throat, the bacteria has settled into the lining or mucosa of the pharyngeal area and produces many small abscesses. These abscesses, as small as they are, mature almost overnight and drain into the surrounding tissue. The infection spreads rapidly into the parapharyngeal and intermandibular lymph nodes, which in turn, causes them to swell and abscess. These abscesses will mature and drain, usually in two to three weeks. When they break and drain, the contents are composed of a thick yellow pus which contains a vast number of the streptococci which contaminate the area and serve as a source of infection to other horses. The caretaker of the infected animal becomes aware of this fact as he or she notices the development of these abscesses. The intermandibular abscess will be located at the bottom of the head between the two jawbones or the mandibules. The parapharyngeal lymph node abscesses will be located below the ear and in the throat region just to the rear of the mandibule or jawbone. These abscesses can be on either side of the pharyngeal or throat region. There may be only one on one side or one on each side, depending on the severity of the infection.

We have a form of strangles called the “bastard strangles.” In this form, abscesses may develop in various parts of the body, both internally and externally. The external abscesses pose no problem at all. I have drained abscesses on strangles infected animals on nearly every part of their bodies. Some of them, especially in the rear quarters, will get quite large.

The abscesses which occur internally are a different story. They may develop in the lungs, heart, liver, kidneys and especially in the peritoneal or belly cavity. These horses will become worthless and if such an abscess would rupture and drain, the animal would most certainly die either immediately or in several days.

Most cases of “bastard strangles” can be prevented. In all of the strangles cases I’ve treated (including infected herds I was placed in charge of), I can truthfully say I’ve never known of a single case of “bastard strangles” where the owners of these animals did as I instructed them.

In outbreaks of strangles the morbidity is very high, often reaching 100% of the susceptible animals. In many cases, it takes a long time for the disease to run its course. Young stock, from near weaning age on up, are at the greatest risk and suffer the most in an outbreak, especially if the disease is of a virulent nature. The victims are at a low health plane and the strangles “hangs on” for a long period of time.

The mortality rate, however, is very low–only 1% of all infected animals. With proper care, some of these would not have had to die.

Strangles in horses can be prevented with the proper use of any one of several vaccines available on the market today. There is even a vaccine which is administered into the nose of the horse via a spray. This is called an intranasal vaccine. It is recommended that vaccines not be given to foals until they are 10 to 12 weeks of age.

In today’s medicine, whole cell bacterins have been largely replaced by M-protein extracts. Most of these vaccines recommend a two or three dose series, each given three weeks apart. After primary immunity is established in this fashion, it is advisable to give an annual booster shot until the animal is four or five years of age.

I might add that most of the vaccines do not seem to fully protect the vaccinated animals against strangles, but they do, however, lessen the severity of the disease.

For a number of years I have used a vaccine for the prevention but also (and especially) for the treatment of strangles. It is a streptococcus equi bacterial extract called Strepguard and is an Intervet product which is somewhat expensive, but it works.

As a general rule, if an animal has had strangles it will become immune to the disease. Occasionally an older horse known to have had the disease will become reinfected. In these cases, the infection will be very mild and of a short duration.

Members of the ass family and mules and hinnies are very resistant to strangles and seldom show symptoms of an infection. That is not to say that they cannot get the disease but generally if it happens, it will be in a very mild form and will rapidly resolve itself.

The treatment of strangles depends largely upon when you are aware that the disease is present in your stock. If exposed animals are checked very closely, especially taking their temperature twice daily, and are treated with penicillin G at the very first onset of the disease, the condition may be dealt with and stopped before other signs of the infection appear. Treatment in these cases with penicillin should be continued for 10 days, with twice-a-day administration of the drug.

While penicillin G is still the antibiotic of choice, cephalosporin and erythromycin are also effective against streptococcus equi.

I’ve mentioned that the frequency of “bastard strangles” can be reduced. This depends largely upon the use of penicillin in the treatment of strangles. I just told you to use penicillin if the animal’s temperature is on the rise and use it over a long period, twice daily. Now, if the abscesses are already forming under and to the rear of the jawbone do not use penicillin until these abscesses break and drain! To use the drug before they drain will impair the animal’s ability to develop an adequate immune response to the strep equi and the disease process will go on and on, lingering around the premises for a long time.

The disease’s name, strangles, comes from the fact that such big abscesses develop in the pharyangeal region that their pressure in the area could actually choke or strangle the horse. If these abscesses develop in your patient and are not draining, you should pack them with hot moist compresses. An old towel kept wet with warm water will do. Never incise an abscess without introducing a needle into the softest area of the abscess. If you do this, generally in a day the abscess will “come to a head,” rupture and drain at the precise area where you introduced the needle. You may find upon introducing the needle into the soft spot, which you palpated on the abscess, that this spot was actually the jugular vein! Whipping out your knife and cutting into that would be a catastrophe!

If an abscess is forming in the pharyngeal area and it is hard and exerting pressure on the breathing passageway, I often give the patient an I.V. dose of oxytetracycline once a day for three days. Usually on the second day the area will “come to a head” and one can hear the breathing improve.

My “ace in-the-hole” for treating strangles, no matter if it involves one animal or a herd, is to take my favorite strangles vaccine, Strepguard, and vaccinate every susceptible animal regardless if it is sick or healthy. I repeat this vaccination in 10 days and repeat it again in another 10 days. It works wonders! Even if all of the animals are sick, they will recover in an amazingly short time and you do not have this disease lasting and lasting for months on end. I am not saying that you do not have to treat the ones that had abscesses when you vaccinated the first time, but you will bring the disease process to a much, much earlier end than if it ran its natural course. It works even if only one animal is involved. These animals build their own immunity and in these vaccinated herds I have never had a case of “bastard strangles.”

Keep the patients in a clean, dry, environment. Do not allow them to be in a cold rain or snowstorm. Above all, do not force exercise sick or exposed animals.

I hope I have helped you, the reader, to deal with one of the most common and vexing infectious diseases of the horse, mule and ass. If strangles strikes your stock, get right on it. Don’t fool around. You will save a lot of money in the end.

And last, a historical note:

Early on in the War Between the States, General George B. McClellan, the commander of the Army of the Potomac, drew up plans for a massive assault on General Robert E. Lee and his Army of Northern Virginia.

The whole battle plan had to be scrapped and postponed due to a severe infection of strangles occurring in the Union remount stations, which supplied cavalry mounts, and artillery horses to McClellan’s army. Without these replacement horses, his army could not take the offensive as planned.