Strangles in Horses:

     Strangles in HorsesStrangles in Horses2Strangles in Horses3

 

Strangles

 

Etiology and Pathogenesis:

Clinical Findings:

  1. The incubation period of strangles is 3–14 days, and the first sign of infection is fever (103–106°F [39.4–41.1°C]).
  2. Within 24–48 hr of the initial fever spike, the horse will exhibit signs typical of strangles, including mucoid to mucopurulent nasal discharge, depression, and submandibular lymphadenopathy.
  3. Horses with retropharyngeal lymph node involvement have difficulty swallowing, inspiratory respiratory noise (compression of the dorsal pharyngeal wall), and extended head and neck.
  4. Older animals with residual immunity may develop an atypical or catarrhal form of the disease with mucoid nasal discharge, cough, and mild fever. Metastatic strangles (“bastard strangles”) is characterized by abscessation in other lymph nodes of the body, particularly the lymph nodes in the abdomen and, less frequently, the thorax.

Streptococcus Equi Retropharyngeal Abscess

Streptococcus equi retropharyngeal abscess

Strangles, Brain Abscess

Strangles brain abscess

Strangles

Strangles

 

Diagnosis:

  1. Diagnosis is confirmed by bacterial culture of exudate from abscesses or nasal swab samples. CBC reveals neutrophilic leukocytosis and hyperfibrinogenemia. Serum biochemical analysis is typically unremarkable.
  2. Complicated cases may require endoscopic examination of the upper respiratory tract (including the guttural pouches), ultrasonographic examination of the retropharyngeal area, or radiographic examination of the skull to identify the location and extent of retropharyngeal abscesses.

 

Treatment:

Ruptured Submandibular Abscesses

Ruptured submandibular abscesses

Prevention:

  1. Postexposure immunity is prolonged after natural disease in most horses, and protection is associated with local (nasal mucosa) production of antibody against the antiphagocytic M protein.
  2. The clinical attack rate of strangles is reduced by 50% in horses vaccinated with IM products that do not induce mucosal immunity. Local (mucosal) production of antibody requires mucosal antigen stimulation.
  3. An intranasal vaccine containing a live attenuated strain of S equi equi was designed to elicit a mucosal immunologic response. This attenuated strain is not temperature sensitive (inactivated by core body temperature), like the intranasal influenza vaccine.
  4. Reported complications include S equi equi abscesses at subsequent IM injection sites (live bacteria on hands of administrator), submandibular lymphadenophathy, serous nasal discharge, and purpura hemorrhagica.

 

Control:

  1. Clinically affected horses should be physically separated from the herd and cared for by separate caretakers.
  2. The rectal temperature of all horses exposed to strangles should be obtained twice daily, and horses developing fever should be isolated (and potentially treated with penicillin).
  3. Contaminated equipment should be cleaned with detergent and disinfected using chlorhexidine gluconate or glutaraldehyde.
  4. Flies can transmit infection mechanically; therefore, efforts should be made to control the fly population during an outbreak.
  5. Farriers, trainers, and veterinarians should wear protective clothing or change clothes before traveling to the next equine facility.
  6. Additions to the herd should be carefully scrutinized for evidence of disease or shedding (nasopharyngeal culture) and quarantined for 14–21 days.
  7. Two negative nasal swab cultures should be obtained during the quarantine period. Most horses continue to shed S equi for ~1 mo after recovery. Three negative nasopharyngeal swabs, at intervals of 4–7 days, should be obtained before release from quarantine, and the minimal isolation period should be 1 mo.
  8. Prolonged bacterial shedding (up to 18 mo) has been identified in a small number of horses. Guttural pouch empyema is the source of infection in most prolonged carrier states.
  9. Bacterial culture of nasopharyngeal swab and/or guttural pouch lavage is used to identify persistent carriers.