A 45-year-old woman who recently returned from a safari in sub-Saharan Africa presents with intermittent episodes of high fever, chills, and profuse sweating over the past three weeks. Her vital signs on presentation include: • Temperature: 38.8°C (101.8°F) • Heart rate: 110/min • Blood pressure: 110/70 mm Hg A peripheral blood smear reveals extracellular flagellated protozoa that exhibit a dense coat of variable surface glycoproteins. Based on these findings, which of the following best explains the mechanism by which the causative organism evades the host immune response?