Which combination of findings supports Lawsonia infection in a horse?

• A. POCUS shows thickened intestines, PCR positive, gross mucosa thickening to necrohemorrhagic enteritis, and histology with enterocyte hyperplasia and comma-shaped bacteria
• B. Normal ultrasound with negative PCR
• C. Thickened intestines on ultrasound but histology shows viral inclusions
• D. Positive blood culture for Lawsonia

Answer: (A)

Lawsonia intracellularis infection in horses causes proliferative enteropathy, where the intestinal mucosa undergoes hyperplasia and becomes thickened. Diagnosing it typically relies on a combination of imaging, gross pathology, histology, and molecular detection. The findings described—ultrasound showing thickened intestines, a positive PCR for Lawsonia, gross mucosal thickening that can be necrohemorrhagic, and histology showing enterocyte hyperplasia with intracellular comma-shaped bacteria—fit this disease pattern precisely. The thickened intestinal walls reflect mucosal proliferation; the PCR confirms the organism’s presence; the gross appearance highlights the severe mucosal change; and histology with enterocyte hyperplasia and intracellular organisms is a classic hallmark of Lawsonia proliferative enteropathy.

Other options don’t align as well: a normal ultrasound and negative PCR would argue against infection; histology showing viral inclusions suggests a different viral enteritis; and a positive blood culture for Lawsonia is not typical because the organism is an intracellular pathogen and not reliably cultured from blood.