East Coast fever is associated with which ONE of the following?

• A. Infection of white blood cells and symptoms associated with uncontrolled proliferation of these cells
• B. Infection of platelets and symptoms associated with abnormal blood clotting
• C. Infection of red blood cells and symptoms associated with anemia
• D. Infection of endothelial cells in the brain and thorax, and symptoms associated with an outpouring of fluid from the blood vessels

Answer: (A)

East Coast fever is caused by Theileria parva, a parasite that targets white blood cells. When sporozoites invade lymphocytes, they transform into schizonts that drive uncontrolled proliferation of the infected cells. This leukocyte proliferation leads to pronounced lymphadenopathy, fever, edema, and other systemic signs characteristic of the disease. Although merozoites later appear in red blood cells, the defining pathology is infection of white blood cells with uncontrolled proliferation. The other targets—platelets, red blood cells, or endothelial cells with vascular leakage—do not reflect the primary mechanism of East Coast fever.