Aldo Castellani. Portrait of Aldo Castellani, (1877-1971) Italian physician and bacteriologist. In 1902-03 he discovered the parasites, Trypanosoma sp, which cause sleeping sickness (Trypanosomiasis). The parasites were found in cerebrospinal fluid. They are transmitted by the bites of the tsetse fly and attack the spleen and nervous sytem. Castellani also discovered the spiral-shaped bacteria, Treponema pertenue, which causes yaws. Yaws is a skin disease contracted through contact with an infected person. It causes lesions on the skin; in advanced stages it leads to ulceration and bone destruction.