The causative agent and vector were identified in 1903 by David Bruce, and the subspecies of the protozoa were differentiated in 1910. Bruce had earlier shown that T. brucei was the cause of a similar disease in horses and cattle that was transmitted by the tsetse fly (Glossina morsitans).[66]

The first effective treatment, atoxyl, an arsenic-based drug developed by Paul Ehrlich and Kiyoshi Shiga, was introduced in 1910, but blindness was a serious side effect.

https://en.wikipedia.org/wiki/African_trypanosomiasis#History

Maybe you confuse it with something else (e.g. https://en.wikipedia.org/wiki/Encephalitis_lethargica )?