Strangles is a highly contagious bacterial infection caused by Streptococcus equi. It can be spread by horse-to-horse contact or when humans, tack, drinking troughs, etc. becoming contaminated with the pus or nasal discharge from affected horses. Horses that have not been exposed to the bacteria in recent years are particularly susceptible because their immunity usually declines over time.
Early signs of Strangles include fever (Temperature > 102 F), depression and a nasal discharge which progresses from clear to thick and yellow. A few days later most horses develop painful swelling of the lymph nodes under the jaw, which form abscesses that eventually rupture and discharge pus. Many veterinarians prefer not to use antibiotics on uncomplicated cases and advocate hot packs applied to the lower jaw to help abscesses mature to a point where they can safely be opened. Once open, the abscess cavities may be flushed with dilute povidone-iodine solutions until they heal. Treating these uncomplicated cases with antibiotics is rarely necessary and may delay abscesses from maturing. Horses usually recover fully after rupture of these abscesses.
A diagnosis of Strangles is confirmed when S equi is identified from swabs. A more serious condition arises in some horses that develop noticeable swelling in lymph nodes in the throatlatch area. These horses are often very reluctant to eat due to pain and may stand with their head outstretched and nose poked forward to aid in breathing.
The term "Strangles" was coined because of the potential for lymph nodes to compress the upper airway. Horses with these symptoms need immediate veterinary attention and require a more aggressive treatment approach. Anti-inflammatories and antibiotics such as penicillin should be given and the horse may need a referral to a veterinary hospital to keep their airway open and the horse well hydrated.
If Strangles is identified on a farm, it is important to set up a management protocol and isolate all the horses with symptoms to one area. To attempt to prevent spread of infection, this area should have separate farm utensils and grooming equipment. All organic material (feed, manure, bedding) should be completely cleaned from contaminated areas and kept away from unaffected horses. Equipment, stables, fences, trailers, etc. should be thoroughly disinfected using a phenolic disinfectant. Clothes should be changed and hands washed prior to handling other healthy horses on the farm.
Several measures can help to decrease the likelihood and spread of Strangles. Intramuscular and intranasal vaccines are available. These vaccines often decrease the severity of the symptoms in infected horses but do not always completely prevent the disease from occurring. Ideally, new horses entering a farm should be isolated for 2-3 weeks and their temperatures checked regularly. Any horse with a high temperature, nasal discharge, difficulty in swallowing, or swollen glands should have their throat or guttural pouch swabbed for the S equi bacteria. Unfortunately, some horses become symptomless carriers of Strangles and harbor the bacteria in their guttural pouches. This is probably the most important cause of recurring infection on some farms. To identify chronic carriers, several collections of swabs are necessary.