Description of the Disease
Strangles is the name of the condition caused by the bacteria Streptococcus equi. S. equi is a highly contagious bacterium that gains entrance through the nose and mouth and colonizes the nasopharyngeal area in the back of the nose and throat. Horses infected with S. equi almost always have a high fever often above 104° F, are depressed, cough, and have excessive cloudy nasal discharge.
The bacteria also travel into the lymph nodes under the jaw and back of the throat, causing large abscesses that can obstruct the airway of the horse, hence the name “Strangles”. On some occasions lymph nodes in other parts of the body, such as the abdomen and thorax, become infected resulting in a condition called “bastard strangles”. These horses are extremely difficult to treat.
Treatment
The controversial part of Strangles is the treatment. For most horses there is no treatment necessary besides supportive care. A clean, dry stall or paddock away from other horses, clean water, and food that can be easily eaten is usually all that is needed. A soft moist pelleted feed may be easier for horses that have difficulty swallowing.
If the horse is quite depressed and not wanting to eat, non-steroidal anti-inflammatory medications such as phenylbutazone(“bute”) or flunixamine (Banamine) can be helpful. If there are large, abscessed lymph nodes under the jaw, treatment should be directed at encouraging them to mature and rupture such using hot packs and poultices (icthammol or magnapaste). Veterinary assistance may be needed to lance and drain the abscess. Daily flushing with saline and betadine solution is recommended.
Antibiotics are generally discouraged. Even though they will bring the fever down and make the horse feel better, they may slow down the maturation of the abscess, thus increasing the likelihood of a slower recovery and possible recurrence. An exception to this would be the horse that is extremely sick with lymph nodes obstructing the airways causing difficulty breathing. Some of these horses may even need a tracheotomy or breathing tube placed in the middle of the windpipe to allow them to breathe.
There is some argument about antibiotic usage very early in the disease process when the horse first spikes a fever and has no lymph node enlargement. In outbreak situations this can be helpful in limiting a full blown strangles infection. It should be noted that early treated horses may not develop very good immunity to future S. equi exposures and in fact might develop strangles if exposed to active cases after the antibiotics are discontinued. Your herd veterinarian can help you decide whether antibiotic treatment is warranted or not for your specific barn situation.
Transmission of Strangles
To prevent Strangles you need to understand how the bacteria are spread. Transmission occurs when there is direct or indirect contact with nasal discharges from infected horses. Direct transfer of bacteria happens with horse to horse contact while indirect transmission occurs with sharing of contaminated stalls, utensils, twitches, tack, and even people. Of particular concern are water sources. If horses drink at a community source, their mucous drains into the water, easily spreading the bacteria to any other horse that uses that water source.
It was previously thought that once your farm has had Strangles you may always have a problem (i.e. “It’s in the barn forever”). S. equi is actually fairly sensitive to environmental destruction persisting in the surroundings usually less than two months. It’s susceptible to drying, heat, sunlight, and most disinfectants.
Recent information indicates that carrier horses may be a more important source of persistent outbreaks on farms. The majority of horses that have had a case of strangles will shed the organism for 4-6 weeks, so isolation of these animals during this timeframe is important.
However, it is now recognized that a small percentage of horses may become long-term shedders of S. equi. These horses are clinically normal but maintain an infection in the guttural pouch and shed bacteria for months or years. When these horses are moved from stable to stable or go to shows, they can infect horses that have not been exposed or vaccinated.
Carrier horses are difficult to identify because they appear normal. Suspect horses can be tested using a polymerase chain reaction (PCR) test that looks for S. equi DNA from nasal swabs or washes. This test can be useful for establishing infection status before transport and commingling of horses.
Horses that have had strangles infections generally have very good immunity to subsequent exposure for more than five years, however vaccination may be helpful in certain situations. In the past, S. equi vaccines were only partially protective and carried significant side effects.
The recent development of an intranasal vaccine (Pinnacle IN®) has proved to be more effective with fewer side effects than the IM vaccines. The IN vaccine is also a modified live vaccine which usually induces much better immunity than the IM killed products. It is extremely important with intranasal products (especially S. equi) that they are given after your other IM vaccines, because you may get contamination of the S. equi on the skin which can be carried through a needle and cause an abscess.
Most sources do not recommend vaccination of horses that are in direct contact with active strangles cases for fear of inducing an active infection. Horses that are traveling to barns with known strangles cases or horses with no direct contact with infected horses or mucous should be vaccinated. Immunity takes at least 2 weeks to develop.
Most importantly call your veterinarian if you think you may have strangles on your farm or if your horse may have exposure to other horses with strangles. Every farm situation is unique and strategies to reduce infection rates may vary.
Copyright © 2008 The NW Horse Source, LLC
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