Proliferative and granulomatous ileitis in a pig naturally infected with Lawsonia intracellularis

BACKGROUND: Granulomatous enteritis in pigs is mostly associated with porcine circovirus 2 systemic disease (PCV2-SD) but less often caused by fungi, Salmonella spp., foreign bodies, Mycobacterium spp. or Lawsonia intracellularis. This unusual and rare presentation of Lawsonia intracellularis infection can only be diagnosed by histopathological and immunohistochemical confirmation. CASE PRESENTATION: Postmortem examination was performed in three 9-10-week-old post-weaned growing pigs from an outdoor farm submitted with a clinical history of increased mortality and wasting over the last two batches. Gross findings in all animals included poor body condition, segmental fibrino-necrotizing enteritis and catarrhal colitis. Histopathological examination identified chronic segmental proliferative enteritis with concurrent granulomatous inflammation of the submucosa and Peyer's patches in one animal (pig A). Lawsonia intracellularis was demonstrated in the apical cytoplasm of proliferating crypt enterocytes and in multinucleated giant cells and macrophages of the lamina propria and submucosa by Warthin-Starry stain and immunohistochemistry. PCV2 antigen was not detected in the intestinal lesions or in other lymphoid tissues by immunohistochemistry. Mycobacteriosis was ruled out by means of Ziehl Neelsen stain. Selective culture of intestinal contents for Salmonella spp. was negative and Brachyspira pilosicoli was isolated and identified by PCR from two animals (pigs A and C). This spirochete could have contributed to the colitis and wasting in these animals. Porcine reproductive and respiratory syndrome virus involvement was discarded in the three pigs by spleen RT-PCR. CONCLUSION: This case report highlights Lawsonia intracellularis as a rare but significant differential diagnosis for granulomatous enteritis in pigs and emphasizes the importance of achieving a definitive diagnosis by excluding PCV2-SD and demonstrating co-localization of the bacterium with granulomatous inflammation by Warthin-Starry stain and immunohistochemistry.