The organism causing heartwater, Ehrlichia ruminantium, causes edema or fluid accumulation because it infects which cells?

• A. Leukocytes
• B. Endothelial cells
• C. Respiratory epithelial cells
• D. Red blood cells

Answer: (B)

Edema in heartwater results from the organism replicating inside vascular endothelial cells lining small blood vessels. This endothelial infection causes vasculitis and damage to the vessel walls, increasing capillary permeability and leading to leakage of fluid into tissues and body cavities (edema and effusions such as around the heart). Other cell types listed—leukocytes, respiratory epithelial cells, or red blood cells—are not the primary targets in this disease, so they don’t explain the fluid buildup. The endothelial cells are the key site that drives the vascular leakage seen in this condition.