Updated: Mar 13
Strangles is a bacterial infection caused by Streptococcus equi subspecies equi. Infection is achieved by contact with purulent material from infected horses. S. equi is not a normal resident of the equine respiratory tract. Clinical signs include fever, anorexia, depression, mucopurulent nasal discharge, submandibular and retropharyngeal lymph node enlargement, and in some cases dysphagia. Lymph node suppuration develops, and typically the horse recovers uneventfully after rupture of the abscessed lymph nodes. The entire course of disease in an uncomplicated case is about three weeks. Diagnosis is based on the clinical signs and culture of the nasopharynx, draining lymph nodes or sometimes guttural pouches. The name "strangles" refers to the respiratory obstruction due to severe lymph node enlargement that occurs in some cases.
The treatment regimen is controversial and depends on the stage and severity of the infection. First, all affected horses should be isolated from other horses, because S. equi subspecies equi is contagious. If the horse has early clinical signs but no lymph node abscessation, procaine penicillin G may be administered at a dose of 22,000 IU/kg intramuscularly twice daily for 3-10 days. On the other hand, if a lymph node abscess is present, the recommendation is to withhold antimicrobials and to encourage maturation of the abscess by hot packing. If antimicrobials are used in such cases, they may actually prolong the course of disease. Horses that are severely ill or have developed complications should be treated with antimicrobials even if abscesses are present.
Most horses recover uneventfully from strangles, but numerous complications have been reported. Internal abscessation ("bastard strangles") may involve any lymph node and can be particularly difficult to diagnosis and treat. Purpura hemorrhagica, an immune complex reaction to the streptococcal antigen, results in fever, depression, marked edema in the limbs and ventrum, and in some cases, petechiae. Corticosteroids are used in addition to penicillin to treat purpura hemorrhagica. Guttural pouch empyema is seen relatively frequently. Other reported complications include septicemia, dyspnea secondary to retropharyngeal abscessation, laryngeal hemiplegia, endocarditis, and suppurative bronchopnemonia.