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Evaluation of 5 serologic assays to detect Rhodococcus equi pneumonia in foals

Ronald J. MartensDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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Noah D. CohenDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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M. Keith ChaffinDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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Shinji TakaiDepartment of Animal Hygiene, School of Veterinary Medicine and Animal Sciences, Kitasato University, Towada, Japan.

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Charity L. DohertyVeterinary Dynamics Inc, 1525 Templeton Rd, Templeton, CA 93465.

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Arthur B. AnguloTexas Veterinary Medical Diagnostic Laboratory, 1 Sippel Rd, College Station, TX 77843.

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Ronnie F. EdwardsHeart of Texas Equine Clinic, 8533 E Hwy 84, Waco, TX 76705.

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Abstract

Objective—To determine the sensitivity and specificity of 5 serologic assays used to diagnose Rhodococcus equi pneumonia in foals and to determine whether any of the assays could be used to identify affected foals prior to the onset of clinical signs or to differentiate between affected and unaffected foals when clinical signs first become apparent.

Design—Nested case-control study.

Animals—26 foals.

Procedure—Serum samples were obtained from all foals at 2, 4, and 6 or 7 weeks of age. Additional samples were obtained from affected foals at the time of diagnosis of R equi pneumonia and from agematched unaffected foals. Samples were tested with 3 ELISA, an agar gel immunodiffusion assay, and a synergistic hemolysis inhibition assay.

Results—Sensitivity and specificity data indicated that none of the assays could be used to reliably differentiate affected from unaffected foals at any testing period. Proportions of foals that had an increase in test values between paired samples collected at 4 and 6 or 7 weeks of age were not significantly different between affected and unaffected foals. For all assays, result values increased significantly over time; however, the rate of increase was not significantly different between affected and unaffected foals.

Conclusions and Clinical Relevance—Results suggest that serologic assays, whether performed on single or paired samples, cannot be used to reliably establish, confirm, or exclude a diagnosis of R equi pneumonia in foals. (J Am Vet Med Assoc 2002;221:825–833)

Abstract

Objective—To determine the sensitivity and specificity of 5 serologic assays used to diagnose Rhodococcus equi pneumonia in foals and to determine whether any of the assays could be used to identify affected foals prior to the onset of clinical signs or to differentiate between affected and unaffected foals when clinical signs first become apparent.

Design—Nested case-control study.

Animals—26 foals.

Procedure—Serum samples were obtained from all foals at 2, 4, and 6 or 7 weeks of age. Additional samples were obtained from affected foals at the time of diagnosis of R equi pneumonia and from agematched unaffected foals. Samples were tested with 3 ELISA, an agar gel immunodiffusion assay, and a synergistic hemolysis inhibition assay.

Results—Sensitivity and specificity data indicated that none of the assays could be used to reliably differentiate affected from unaffected foals at any testing period. Proportions of foals that had an increase in test values between paired samples collected at 4 and 6 or 7 weeks of age were not significantly different between affected and unaffected foals. For all assays, result values increased significantly over time; however, the rate of increase was not significantly different between affected and unaffected foals.

Conclusions and Clinical Relevance—Results suggest that serologic assays, whether performed on single or paired samples, cannot be used to reliably establish, confirm, or exclude a diagnosis of R equi pneumonia in foals. (J Am Vet Med Assoc 2002;221:825–833)