Strangles is a highly contagious disease that affects a horse’s lymph nodes in its upper respiratory tract. It is caused by a bacterium called streptococcus equi. The name, strangles, was coined due to the strangling breathing sounds made by affected horses, caused by the enlarged lymph nodes of the jawbone.
The first signs of strangles are a high fever, poor appetite, and depression. Owners will also notice a thin, watery discharge from the horse’s nostrils. This discharge quickly turns thick and yellow. The horse’s upper respiratory lymph nodes become enlarged, most noticeably the ones between the jawbones. These can even abscess.
Strangles is not usually fatal to horses, but it can be. Strangles can affect horses of any age, but most commonly infects those between one and five years of age. The disease is usually acquired after exposure to another horse that is shedding the streptococcus equi bacteria, either during or after its own bout of the illness.
This commonly occurs when new horses are introduced to an established herd. Although the infectious horse may no longer show signs of strangles, it can still spread the bacteria. Around twenty percent of horses remain contagious for a month after all symptoms vanish.
While direct contact between horses is the most common way that strangles is spread, it can also be spread by contaminated equipment. Improperly cleaned and shared buckets, stalls, and tack can spread the disease between horses. Fortunately, the bacteria die fairly quickly in the environment.
Once a horse is exposed to the bacteria, it will begin to show symptoms in two to six days. If left untreated, it will develop abscessed lymph nodes within one to two weeks after the onset of illness. These lymph nodes will rupture and drain, and the drainage is highly contagious.
Most horses will recover, but around ten percent of untreated horses die, usually from a secondary infection which causes pneumonia. Rarely, the abscesses will spread to other parts of the horse’s body, such as the lungs, internal organs, or even the horse’s brain. This condition is called “bastard strangles.” It is uncommon and is usually fatal.
The treatment of strangles is dependent on the stage of the disease. To control the spread of the strangles bacteria, any new horse with a vague or unknown health history should be isolated for four to six weeks before being added to the general population of the stable or paddock. Nasal swabs can ascertain whether the horse is shedding the streptococcus equi bacteria, but because affected horses shed the bacteria sporadically, one swab test is not enough.
Three nasal swabs over a period of seven days are required before it can be assumed that the horse is negative for strangles. Strangles can also be controlled by vaccinations. Although modern vaccines are more effective than those of the past, providing better protection with fewer side effects, they are not a complete guarantee against the disease. Still, vaccinated horses tend to have a less severe illness if they do contract strangles. Horses cannot contract strangles from the vaccine itself, since it is made from only parts of the pulverized bacterium.
If you suspect that your horse has strangles, notify your veterinarian to confirm the presence of the disease. The sooner a positive diagnosis is reached, the less “down time” the stable will have to tolerate. Also, if a horse begins antibiotic treatment in the early stages of the disease, lymph node abscesses can be prevented.
Old veterinary practices warned against using antibiotics for strangles because of the suspicion that it could cause bastard strangles. However, there is no evidence that this is the case. Usually, when horses are treated with antibiotics in the early stages of strangles, they will recover unless the antibiotics are not given in the correct amounts or are stopped too soon. Even if the horse is on antibiotic therapy, it must be isolated from the rest of the stable and herd to prevent the spread of the illness.
However, once lymph nodes have enlarged and become abscessed, antibiotic treatment will only prolong the horse’s illness. It is better to allow the abscess to open, or have the veterinarian lance it, so that it may drain. The best treatment at this point is to flush the drainage site, keep the area as clean as possible, and to maintain strict isolation of the ill horse.
If your horse was stabled near one who had strangles at a show or rodeo, it is reasonable to treat it with antibiotics for at least six days after exposure. This is because horses usually don’t show the first signs of the disease for two to six days. However, if your horse is kept in a barn where other horses have strangles, antibiotics will do little to prevent it from getting the disease.
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