Lawsonia intracellularis and Virulent Rhodococcus equi Infection in a Thoroughbred Colt

• Published in: Journal of comparative pathology Vol. 143; no. 4; pp. 303 - 308
• Main Authors: Shimizu, C., Shibahara, T., Takai, S., Kasuya, K., Chikuba, T., Murakoshi, N., Kobayashi, H., Kubo, M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-11-2010
• Subjects: Actinomycetales Infections - microbiology; Actinomycetales Infections - pathology; Actinomycetales Infections - veterinary; Animals; Desulfovibrionaceae Infections - microbiology; Desulfovibrionaceae Infections - pathology; Desulfovibrionaceae Infections - veterinary; diarrhoea; equine proliferative enteropathy; Horse Diseases - microbiology; Horse Diseases - pathology; Horses; Ileum - microbiology; Ileum - pathology; Immunohistochemistry; Intestinal Mucosa - microbiology; Intestinal Mucosa - pathology; Lawsonia Bacteria; Lawsonia intracellularis; Liver - microbiology; Liver - pathology; Polymerase Chain Reaction; Rhodococcus equi; Rhodococcus equi; diarrhoea; equine proliferative enteropathy; Lawsonia intracellularis
• ISSN: 0021-9975; 1532-3129
• DOI: 10.1016/j.jcpa.2010.03.005

A 26-month-old thoroughbred colt with a 4-month history of continuous diarrhoea and weight loss was subject to necropsy examination. The small intestinal mucosa was thickened and this change particularly affected the terminal ileum. Microscopical examination revealed multifocal epithelial hyperplasia, with multifocal granulomas and marked lymphocytic infiltration of the lamina propria. Numerous gram-negative argyrophilic curved bacilli were observed within the cytoplasm of affected enterocytes. Macrophages and epithelioid cells forming the granulomas had abundant, lightly eosinophilic, foamy cytoplasm, with occasional large, clear vacuoles containing gram-positive coccobacilli. Immunohistochemical studies suggested that the argyrophilic bacilli were
Lawsonia intracellularis and the gram-positive coccobacilli were
Rhodococcus equi.
L. intracellularis-specific DNA fragments were amplified from the affected ileocaecal mucosa by polymerase chain reaction. Virulent
R. equi (VapA positive) was isolated in pure culture from the liver and mesenteric lymph nodes. These results suggested that the two intracytoplasmic organisms had induced multifocal proliferative and granulomatous enteritis accompanied by severe and extensive lymphocytic infiltration.