Histopathology of Lawsonia infection reveals which key feature?

• A. Enterocyte hyperplasia with comma-shaped bacteria in the apical cytoplasm
• B. Lysis of neutrophils with intracellular bacteria
• C. Granulomatous inflammation of the submucosa
• D. Absence of bacteria in tissue

Answer: (A)

Lawsonia intracellularis causes proliferative enteropathy by infecting intestinal enterocytes and pushing them to multiply, so the hallmark on histology is enterocyte hyperplasia with the bacteria located inside the enterocytes’ cytoplasm, especially near the apical border. The intracellular, often curved or comma-shaped organisms within the apical cytoplasm of enterocytes best fit this feature, and special stains or immunohistochemistry can highlight them.

Other patterns don’t fit: lysis of neutrophils with intracellular bacteria isn’t characteristic of Lawsonia infection, granulomatous inflammation of the submucosa isn’t the typical lesion, and the presence of bacteria in tissue is expected, not absence.