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Bacterial Disease - Strangles

Synonyms:

Equine Distemper and Infectious adenitis.

Etiology

Strangles is caused by Streptococcus equi subspecies equi. It is an obligate, gram positive and cocco-bacillus organism. The organism expresses beta haemolysin around the colonies in blood agar. Similarities exists between the genome of S.equi and S.zooepidemicus.

Epidemiology

Highly contagious disease that affects horses of all ages but is most

common in young animals. Prolonged carrier state in asymptomatic animals

Transmission

Direct and indirect contact with fomites are important for infection. Inhalation also possible. Through skin wound from external environment.

Host affected

Horses, donkeys and mules around the world are susceptible. Morbidity rate is (20-100%) usually more in foals and yearlings than in adults. Age specific attack rates in foals 20-4o% and brood mares 20%. Case fatality rate is 10% in untreated and 1-2% in treated horses have been recorded.Outbreaks occurs frequently in breeding farms, polo and race horses

Clinical signs

Acute onset of fever, anorexia, depression, submandibular and pharyngeal lymphadenopathy with abscessation and rupture, and copious

purulent nasal discharge. Metastatic infection in other organ systems

Strangles in Burros

Slow developing debilitated disease and have caseation and calcification of abdominal lymphnodes.

Chronic form (Metastatic infection or Bastard strangles)

It is a chronic illness eventually leading to death. Arise due to bacteraemia or extension of infection in lymphnodes. Heart valves, brain, eyes, joints, tendons, sheath are affected. Abscess in brain leads to depression, head pressing, abdominal gait, circling and seizures.

Complications

  • » Suppurative necrotic bronchopneumonia, due to aspiration of pus from ruptured abscess in the upper airways / metastatic infection of lungs.
  • » Spreading of infection from RLN into guttural pouches due to rupture-uni/bilateral nasal discharge.

Clinical pathology

Culture of S. equi from nasal and abscess discharges. Polymerase chain reaction (PCR) of nasal, pharyngeal or guttural pouch swabs. High

serum antibody titer to SeM

Lesions

Caseous lymphadenopathy with rhinitis and pharyngitis, pneumonia and metastatic infection in severe cases Suppuration of liver, spleen, lungs, pleura and peritoneum. Meningitis, hyperesthesia, rigidity of the neck. Lesions in guttural pouch and in various lymphnodes.

Diagnostic confirmation

Culture of S. equi

Treatment

Systemic administration of penicillin. Local treatment of abscesses

Control

Isolation and quarantine of cases and new admissions to barns and stables. Detection of carrier status by PCR and/or culture of guttural pouch washings. Vaccination may reduce the case attack rate and severity of disease.


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