I recently read about an outbreak of strangles in a horse rescue in Roanoke Virginia1. It reiterated to me of how this serious illness can be.
Strangles is an ancient disease with the first recorded report in 12512. It is caused by the bacteria Streptococcus Equi and is one of the most commonly diagnosed infectious diseases of horses in the world2. While it affects mainly young horses I have seen cases in older horses, as old as 30 years of age in one case. The bacterium infects the lymphatic system of the head causing abscesses to form in the lymph nodes. Strangles gets its name from the endangered lymph nodes under the jaw and neck. Those lymph nodes can enlarge to the point that they cause breathing difficulties. Severely affected horses may need a tracheotomy to breathe. Strangles also cases a high fever (sometimes >105.0� F)2 and decreased appetite.
The disease is not spread to humans, but is easily transmissible between horses. It is spread by direct contact with nasal secretions or drainage from abscessed lymph nodes. The bacteria are also easily spread by objects contaminated with puss or nasal secretions. Halters, feed buckets, tack, boots, clothing and stalls can all be contaminated with the bacteria and serves as a source of exposure to uninfected horses. The bacteria can survive in water for a month. The most common cause of infection is apparently healthy horses that can shed the bacteria for months to years2.
There is a great deal of disagreement as to the best form of treatment. Many veterinarians advocate no treatment at all as most horses will clear the bacteria and recover on their own. Horses severe enough to require tracheotomy do however need antibiotic therapy and supportive care. The infection can also spread in internal lymph nodes and can also cause a serious immune reaction called purpura hemorrhagica2.
Even if most horses are able to clear the bacteria on their own the infection can spread so quickly that most of the horses in the barn can become infected. Affected horses will usually be unable to compete or race and brood mares may be unable to conceive. I saw an outbreak serious enough on one breeding farm that the stable lost an entire breeding season.
Prevention is ideally based on preventing exposure, but because many carriers show no clinic signs, this is practically impossible. I recommend vaccinating all at risk horses. At risk horses include horses that travel, or are stabled at a barn with horses that travel, as travel increases exposure to infected horses. Isolated horses are at very low risk of contracting the disease.
Two vaccines are available, an injectable and an intranasal. I believe that the intranasal is the better of the two. Even though neither vaccine can completely eliminate the possibility of infection they will decrease severity and shorten the clinical course of the disease. Because improper vaccine administration will decrease the efficacy of the vaccine and can cause life threatening reactions at the site of administration they should only be given by your veterinarian.
1. roanoke.com
2. AAEP Understanding Equine Strangles