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  • Author or Editor: Ashley G. Boyle x
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OBJECTIVE To develop a risk prediction model for factors associated with an SeM-specific antibody titer ≥ 3,200 in horses after naturally occurring outbreaks of Streptococcus equi subsp equi infection and to validate this model.

DESIGN Case-control study.

ANIMALS 245 horses: 57 horses involved in strangles outbreaks (case horses) and 188 healthy horses (control horses).

PROCEDURES Serum samples were obtained from the 57 cases over a 27.5-month period after the start of outbreaks; serum samples were obtained once from the 188 controls. A Bayesian mixed-effects logistic regression model was used to assess potential risk factors associated with an antibody titer ≥ 3,200 in the case horses. A cutoff probability for an SeM-specific titer ≥ 3,200 was determined, and the model was externally validated in the control horses. Only variables with a 95% credibility interval that did not overlap with a value of 1 were considered significant.

RESULTS 9 of 57 (6%) case horses had at least 1 titer ≥ 3,200, and 7 of 188 (3.7%) of control horses had a titer ≥ 3,200. The following variables were found to be significantly associated with a titer ≥ 3,200 in cases: farm size > 20 horses (OR, 0.11), history of clinically evident disease (OR, 7.92), and male sex (OR, 0.11). The model had 100% sensitivity but only 24% specificity when applied to the 188 control horses (area under the receiver operating characteristic curve = 0.62.)

CONCLUSIONS AND CLINICAL RELEVANCE Although the Bayesian mixed-effects logistic regression model developed in this study did not perform well, it may prove useful as an initial screening tool prior to vaccination. We suggest that SeM-specific antibody titer be measured prior to vaccination when our model predicts a titer ≥ 3,200.

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in Journal of the American Veterinary Medical Association


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.

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in Journal of the American Veterinary Medical Association


Objective—To identify factors associated with an increased likelihood that horses would have a serum Streptococcus equi SeM-specific antibody titer ≥ 1:1,600.

Design—Cross-sectional study.

Animals—188 healthy client-owned horses.

Procedures—A single serum sample from each horse was tested for SeM-specific antibody titer with an ELISA. Multivariate logistic regression was used to identify factors associated with having a titer ≥ 1:1,600.

Results—Age, breed, and vaccination status were significantly associated with the likelihood of having a titer ≥ 1:1,600. The odds of having a titer ≥ 1:1,600 increased by a factor of 1.07 with each 1-year increase in age. Quarter Horses and horses of other breeds were 4.08 times as likely as were Thoroughbreds and warmbloods to have a titer this high. Horses that had previously received an intranasal S equi vaccine were 4.7 times as likely as were horses without any history of vaccination to have a titer this high.

Conclusions and Clinical Relevance—Results indicated that older horses, horses other than Thoroughbreds and warmbloods, and horses that had been vaccinated with an attenuated-live intranasal S equi vaccine between 1 and 3 years previously had an increased likelihood of having a serum SeM-specific antibody titer ≥ 1:1,600.

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in Journal of the American Veterinary Medical Association


Objective—To assess data regarding clinical features, clinicopathologic and blood gas variables, and outcome from horse and mule foals with confirmed neonatal isoerythrolysis (NI).

Design—Retrospective case series.

Animals—17 horse and 1 mule foals.

Procedure—Medical records of foals (< 14 days old) with NI were reviewed. Information collected included signalment; clinical examination findings; results of hematologic, serum and plasma biochemical, and venous blood gas analyses and urinalysis; treatments; and outcome.

Results—Data from 17 horse foals and 1 mule foal with NI (mean age, 71 hours) were evaluated. Many foals had high serum indirect and direct bilirubin concentrations and sorbitol dehydrogenase activity. Whole blood immunoglobulin concentrations were < 400 mg/dL in 4 of 15 foals. Fresh whole blood transfusions were administered to 10 of 18 foals. Among the blood factors implicated in 11 foals, one (Dg) had not previously been associated with NI. Of 10 foals that received blood transfusions, 7 had significant improvements in Hct and hemoglobin concentration and 2 had significant improvements in central venous oxygen tension. Fifteen foals survived to discharge.

Conclusions and Clinical Relevance—Data suggest that blood factor Dg may be associated with NI in foals. Liver disease may be concurrent with NI in foals, and NI can develop in foals with inadequate passive transfer of colostral antibodies. Whole blood transfusions were successful at increasing oxygencarrying capacity and improving peripheral tissue oxygenation in NI-affected foals. With appropriate treatment, the prognosis for foals with NI is good. (J Am Vet Med Assoc 2005;227:1276–1283)

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in Journal of the American Veterinary Medical Association