Lecture 28

• T or F: Strangles is one of the most important diseases of horses in developed countries, accounting up to 30% of reported infectious disease episodes.

  True
• Strangles is important for the death it causes but also because of what?


  -disruption of management of commercial horse establishments

  -time necessary to treat affected horses

  -esthetic unpleasantness of the horses with runny noses and draining abscesses
• Etiology of strangles:


  Streptococcis equi subsp. equi
• Epidemiology of strangles:


  -highly contagious disease that affects horses of all ages

  -more common in young animals

  -S. equi causes disease in only equids
• Clinical findings of strangles:

  -acute onset of fever, anorexia, depression

  -submandibular and pharyngeal lymphadenopathy w abscessation and rupture

  -Copious purulent nasal discharge

  -Metastatic infection in other organ systems
• Lesions seen with strangles:


  caseous lymphadenopathy with rhinitis and pharyngitis, pneumonia, and metastatic infection in severe cases
• Diagnostic confirmation for strangles:

  Culture of S. equi or PCR
• Treatment for strangles:


  systemic administration of Penicillin and local treatment of abscesses
• Control of strangles:


  Isolation and testing

  Vaccination
• Characteristics of Streptococcus equi subsp. equi (S. equi):


  -Gram positive cocci

  -Facultative anaerobic

  -Catalase and coagulase negative

  -Beta-hemolytic

  -Highly adapted to Equidae
• Where does strangles occur?

  horses, ponies, donkeys, and mules worldwide
• T or F: Strangles can affect horses of any age although morbidity rate is higher in younger horses.


  True
• Case fatality rate without treatment is about?

  9%
• Case fatality with adequate early treatment may be?

  1-2%
• Where are outbreaks of strangles seen?


  breeding farms and in polo and racing stables
• Why are outbreaks seen at these places?


  infection is introduced by asymptomatic new arrivals or horses that are taken to fairs and riding schools.
• S. equi is an:

  obligate parasite of horses
• All infections are attributable to transmission from?

  infected horses either directly or by fomites
• Source of infection:


  nasal and abscess discharges from infected animals
• How long can strangles survive in the environment for?

  less than 3 days
• How many recovered horses (%) have persistent infection and are important sources of infection?

  10-40%
• Detection of carriers via


  PCR on nasal swabs or guttural pouch lavage fluid
• Resistance to the disease is associated with the production of

  serum and mucosal antibodies to the streptococcal M protein (SeM)
• Around what percent of horses that recover from the disease do not develop protective immunity?


  25%
• Virulence of S equi is attributable to the presence of:


  -M proteins on the surface of bacteria

  -Hyaluronic acid capsule

  -Production of a Leukocidal toxin
• M proteins are associated with?

  -Adhesion to oral nasal and pharyngeal tissue

  -Invasion of pharyngeal tonsils

  -Evasion of the innate immunity
• Capsule provides resistance to

  phagocytosis
• What happens following adhesion?


  S. equi lodge and multiply in pharyngeal and tonsillar lymphoid tissue
• Toxins produced by S. equi cause

  direct cell damage
• Migration of neutrophils into the lymph nodes causes


  swelling and abscessation
• T or F: Most abscess eventually rupture and drain and infection resolves with development of an effective immune response.

  True
• Nasal shedding persists for

  2-3 weeks, but longer in exceptional cases
• Death is rare and usually due to


  pneumonia caused by aspuration of the infected material or due to asphyxiation
• What is the second most common cause of death?

  Upper airway obstruction and impairment of organ function by metastatic infection
• Why does metastasis of infection occur?

  bacteremia or spread along lymph vessels.
• Purpura hemorrhagica can occur as a


  sequela to S. equi infection and is associated with high serum antibody tires to SeM.
• Strangles manifests as a

  -acute disease of varying severity, infection of retropharyngeal lymph nodes and guttural pouches

  -a chronic disease associated with metastatic infection of organs distant from respiratory tract
• Severity varies with?


  -age

  -immune status

  -size of inoculum

  -duration of exposure
• Where does the term strangles derive from?


  the enlarges retropharyngeal lymph nodes and guttural pouches causing respiratory distress
• Acute disease is characterized by

  -mucopurulent nasal discharge

  -abscessation of submandibular and retropharyngeal lymph nodes