What is the most likely causative agent If a biology graduate student infection was acquired by black fly bite and she recently visited a tropical region of Africa presents with new visual impairment and the sensation that something is moving in her eye? and she tells you that she is concerned because she had been warned about eye disease transmitted by black flies. When in Africa, she was in a river area, and despite her best efforts she received a lot of black fly bites. She also has some sub-cutaneous nodules.