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Predictor variables for and complications associated with Streptococcus equi subsp equi infection in horses

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  • 1 Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 2 Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 3 Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 4 Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

Abstract

Objective—To evaluate predictor variables for and complications associated with Streptococcus equi subsp equi infection (strangles) in horses.

Design—Retrospective case-control study.

Animals—108 horses with strangles (cases) and 215 horses without strangles (controls).

Procedures—Medical records from January 2005 through July 2012 were reviewed. Cases were defined as horses with clinical signs of strangles (pyrexia, retropharyngeal lymphadenopathy, and mucopurulent nasal discharge) that were associated with a confirmed strangles outbreak or had positive results for S equi on PCR assay or bacteriologic culture. Controls were defined as horses with pyrexia that did not meet the other criteria for cases. Data compared between cases and controls included signalment, clinical signs, diagnostic test results, and disease complications and outcome. Logistic regression was used to identify variables associated with strangles and its complications.

Results—Clinical signs of strangles were not evident in 12 of 25 cases classified as S equi carriers (infected > 40 days). Predictor variables associated with strangles included mucopurulent nasal discharge and external abscesses in the pharyngeal region. Strangles was more likely to be diagnosed in the spring than in the summer. Cases with anemia were more likely to develop purpura hemorrhagica than were cases without anemia. No risk factors were identified for the development of guttural pouch empyema or metastatic abscesses.

Conclusions and Clinical Relevance—Results indicated that not all horses infected with S equi develop clinical signs of strangles. We recommend that guttural pouch endoscopy and lavage with PCR assay of lavage fluid samples be performed to identify S equi carrier horses.

Abstract

Objective—To evaluate predictor variables for and complications associated with Streptococcus equi subsp equi infection (strangles) in horses.

Design—Retrospective case-control study.

Animals—108 horses with strangles (cases) and 215 horses without strangles (controls).

Procedures—Medical records from January 2005 through July 2012 were reviewed. Cases were defined as horses with clinical signs of strangles (pyrexia, retropharyngeal lymphadenopathy, and mucopurulent nasal discharge) that were associated with a confirmed strangles outbreak or had positive results for S equi on PCR assay or bacteriologic culture. Controls were defined as horses with pyrexia that did not meet the other criteria for cases. Data compared between cases and controls included signalment, clinical signs, diagnostic test results, and disease complications and outcome. Logistic regression was used to identify variables associated with strangles and its complications.

Results—Clinical signs of strangles were not evident in 12 of 25 cases classified as S equi carriers (infected > 40 days). Predictor variables associated with strangles included mucopurulent nasal discharge and external abscesses in the pharyngeal region. Strangles was more likely to be diagnosed in the spring than in the summer. Cases with anemia were more likely to develop purpura hemorrhagica than were cases without anemia. No risk factors were identified for the development of guttural pouch empyema or metastatic abscesses.

Conclusions and Clinical Relevance—Results indicated that not all horses infected with S equi develop clinical signs of strangles. We recommend that guttural pouch endoscopy and lavage with PCR assay of lavage fluid samples be performed to identify S equi carrier horses.

Contributor Notes

Dr. Duffee's present address is Matthew J. Ryan Veterinary Hospital, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104.

Presented in part as an oral presentation at the 32nd Annual American College of Veterinary Internal Medicine Forum, Nashville, Tenn, June 2014; and the 32nd Symposium of the Veterinary Comparative Respiratory Society, Kennett Square, Pa, October 2014.

Address correspondence to Dr. Boyle (boylea@vet.upenn.edu).