723C Exam 3

• Streptococcus equi subsp. equi is the etiological agent of strangles

  
• Strangles Epidemiology

  • Highly contagious disease affecting horses of all ages
  • More common in younger animals
  • S. equi only causes disease in equids
• Strangles Clinical Findings

  • Acute onset of fever, anorexia, and depression
  • Submandibular and pharygneal lymphadenopathy with abscessation and rupture
  • Copious purulent nasal discharge
  • Metastatic infection in other organ systems
• Strangles Lesions

  Caseous lymphadenopathy with rhinitis and pharyngitis, pneumonia, and metastatic infection in severe cases
• Strangles Diagnostics

  Culture of S. equi, or PCR
• Strangles Treatment

  Systemic administration of Penicillin and local treatment of abcesses
• Strangles Control

  Isolation and testing; Vaccination
• Streptococcus equi subsp. equi

  • Gram positive, cocci
  • Facultative anaerobe
  • Catalase and coagulase negative
  • Beta-Hemolytic
  • Highly adapted to Equids
• Strangles Species

  • Horses
  • Ponies
  • Donkeys
  • Mules
• Strangles can affect horses of any age, although morbidity is higher in younger horses.
• Strangles fatality without treatment is about 9%; with adequate treatment it may be 1-2%
• Outbreaks frequent on breeding farms, and in polo and racing stables, where infection is introduced by asymptomatic new arrivals or horses taken to fairs/riding schools.
• Strangles transmission

  • Obligate parasite of horses
  • All infections attributable to transmission from infected horses directly or by fomites
• Source of Strangles

  • Nasal and abscess discharges from infected animals
  • From infected pastures, tracks, stalls, feed/water troughs, grooming equipment, or hands/clothes of groomers and veterinarians.
• Strangles survival

  Less than 3 days in environment; prolonged quarantine not required.
• Persistent Strangles Infection

  About 10-40% of recovered horses have persistent infection and are important sources for infection.
• Detection of Strangles Carriers

  PCR on nasal swabs or guttural pouch lavage fluid
• Resistance to Strangles

  • Associated with production of serum and mucosal antibodies to streptococcal M protein (SeM)
  • Animals that had disease less likely than naive animals to develop disease on subsequent exposure
  • Around 25% of horses do NOT develop protective immunity
  • Immunity after natural exposure wanes over time
• Virulence of Strangles

  • M proteins on the surface of bacteria
  • Hyaluronic acid capsule
  • Production of Leukocidal toxin
• M proteins - Virulence

  • Adhere to oral, nasal, and pharyngeal tissue
  • Invade pharyngeal tonsils
  • Evade innate immune system
• Strangles' viral capsule provides resistance to phagocytosis
• Following adhesion, S. equi lodge and multiply in pharyngeal and tonsillar lymphoid tissue.
• Strangles Pathogenesis

  • Toxins produced by S. equi cause direct cell damage
  • Migration of neutrophils into the lymph nodes causes swelling and abscessation
  • Swelling of retropharyngeal lymph nodes may interfere with respiration
  • Most abscesses eventually rupture and drain, resolving with effective immune response
  • Nasal shedding persists for 2-3 weeks, but longer in exceptional cases
• Strangles mortality

  • Death is rare and associated with secondary infections
  • Due to pneumonia caused by aspiration of infected material
  • Due to asphyxiation secondary to upper airway obstruction
  • Due to organ failure by metastatic infection
• Strangles Metastatic Infection

  • Bacteremia or lymph vessel spread
  • Heart Valves, brain, joints, eyes, and other vital organs affected
  • Can cause death
• Strangles - Purpura hemorrhagica


  Can occur as a sequela to S equi infection and is associated with high serum antibody titers to SeM.
• Strangles - Acute disease

  Varying severity, infection of retropharyngeal nodes and guttural pouches
• Strangles - Chronic disease


  Metastatic infection of organs distant from respiratory tract.
• Strangles severity factors

  • Age
  • Immune Status
  • Size of inoculum
  • Duration of exposure
• Strangles Etymology

  Derived from the enlarged retropharyngeal lymph nodes and guttural pouches causing respiratory distress in severely affected animals.
• Acute Strangles disease

  • Characterized by mucopurulent discharge and abscessation of submandibular and retropharyngeal lymph nodes
  • Incubation period of 1-3 weeks
  • Sudden onset of symptoms
• Strangles Essential dates

  • Swelling of lymph nodes in 3-4 days
  • Serum exudate in 10 days, and subsequent rupture
• The most common fatal complication of Strangles is the development of suppurative necrotic bronchopneumonia (aspiration of pus from ruptured abscesses).
• Metastatic strangles infection is also know as Bastard Strangles, occuring in about 1% of affected animals.
• Purpura hemorrhagica


  Immune mediated disease occurring in a subset of Strangles affected horses 1-3 weeks after initial illness.
• Gram positive cocci in chains = Strangles

  
• Strangles Culture

  Colonies usually mucoid, up to 4 mm, surrounded by zone of beta hemolysis

  
• Control of Strangles

  • Penicillin to in-contact and infected horses before development of lymphadenopathy; limited benefit if abscesses already present.
  • Isolation of suspect animals
  • Quarantine horses for 3 weeks before introduction to herd; test negative before introduction.
  • Live Attenuated Intranasal vaccine
  • Avoid overcrowding and mixing age groups, clean building/equipment
• Shipping Fever

  Pneumonic Pastuerellosis of Cattle or Bovine Respiratory Disease
• Characteristic of Pneumonic Pasteurellosis

  Clinical signs of acute bronchopneumonia with toxemia