CVJ / VOL 48 / SEPTEMBER 2007 927 Case Report Rapport de cas An outbreak of Lawsonia intracellularis infection in a standardbred herd in Ontario M. Kimberly J. McGurrin, Modest Vengust, Luis G. Arroyo, John D. Baird Abstract — An outbreak of protein-losing enteropathy associated with Lawsonia intracelluaris infection was diagnosed in 6 standardbred foals from a farm in Ontario. Wildlife exposure may have been involved in the perpetuation of disease in this outbreak. The clinical presentation, treatment, outcomes, and pathological findings are described. Résumé — Éclosion d’infections à Lawsonia intracellularis dans un troupeau de Standardbred en Ontario. Une éclosion d’entéropathies exsudatives associée à une infection à Lawsonia intracellularis a été diagnostiquée chez 6 poulains Standardbred d’une ferme de l’Ontario. Un contact avec la faune pourrait être impliqué dans la perpétuation de la maladie lors de cette éclosion. La présentation clinique, le traitement, l’évolution et les résultats pathologiques sont décrits. (Traduit par Docteur André Blouin) Can Vet J 2007;48:927–930 I n December 2002–January 2003 over a 4-week period, protein-losing enteropathy (PLE) as a result of Lawsonia intracellularis infection was diagnosed in 6 standardbred wean- lings (2 colts, 4 fillies) on a farm in southwestern Ontario. All foals were between 7 and 8 mo of age when presented to the Ontario Veterinary College Veterinary Teaching Hospital (OVC- VTH) for diarrhea and weight loss. All 6 affected foals had been born on this farm and, following weaning at 5 mo of age, had been housed outside in 2 groups according to sex. A further 18 foals on the farm remained clinically normal. No previous cases of PLE had been reported from this particular owner’s herd. However, the farm on which the 6 affected foals had been raised had been purchased 2 y earlier. Six years before, in 1997, while under the management of the previous owner, PLE associ- ated with Lawsonia intracellularis had been diagnosed in 3 foals from this farm at the Animal Health Laboratory, University of Guelph. Between 2000 and 2001, no horses had been on the farm for approximately 12 mo. The 6 foals in this 2002–2003 outbreak were of a different breed and were unrelated to the previous cases. The current owner’s breeding herd had been moved from a farm where PLE had not been identified. All foals had a history of diarrhea, ranging from 12 h to 14 d in duration. History and clinical signs at presentation are listed in Table 1. Two foals (Cases 1, 2) were presented with an acute onset of diarrhea. A third foal (Case 3) was treated at the farm for 7 d with supportive therapy (IV and PO fluids), then deteriorated rapidly, and died, and this foal was presented for postmortem examination to the Animal health Laboratory, University of Guelph. The following day, the 3 other sick foals (Cases 4, 5, 6) were presented to the Ontario Veterinary College. No antimicrobials had been administered to any foal prior to presentation. Case description At the time of presentation, all 5 live foals were diarrheic and in poor body condition. Ventral thoracic edema was noted in cases 1, 2, and 4. Cases 1 and 4 were recumbent at the time of presentation and case 2 became recumbent within 2 h of presentation. Generalized weakness was noted in cases 5 and 6. All 5 foals were clinically dehydrated (estimated at 6% to 10%). Tachycardia (60–100 bpm) and hyperemic mucous membranes were present in all 5 foals. Case 1 was hypothermic (34.0°C). Abdominal ultrasonography was performed on cases 2, 4, 5, and 6. Abnormalities detected included increased free abdomi- nal fluid in cases 2 and 4, and thickened small intestinal wall in cases 2, 4, 5, and 6. Small intestinal mural thickness was measured at 5–12 mm (normal , 3 mm). Thickened loops of small intestine were visualized in cases 2, 4, 5, and 6. The primary differential diagnosis considered at presenta- tion for all 6 cases was PLE due to Lawsonia intracellularis infection. This was considered in 2 cases (1 and 3) because of the signalment and clinical signs and in cases 2, 4, 5, and 6 because of the farm history in addition to the clinical signs and abdominal ultrasonographic findings. Rhodococcus equi infec- tion was not considered as likely, due to the absence of typical respiratory signs. Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1. Address all correspondence to Dr. M. Kimberly J. McGurrin; e-mail: mcgurrin@uoguelph.ca Reprints will not be available from the authors.