Librivox has an audiobook written in the early 1900's that investigates the problem of sleeping sickness.
they blame the epidemic on western traders and explorers who took infected porters with them, spreading the disease to new areas and killing hundreds of thousands of people.
However, what about the Arab traders, including the slave traders, who were in the area at the time? They cite Stanley and Livingstone, but ignore that Livingstone's work was most important in influencing people to oppose the slave trade...
Ironically, what opened Zimbabwe to western expansion was because the rinderpest epidemic killed off enough wildlife to stop the tsetse fly from having enough animals to feed on. There was a tsetse fly free area fenced off when I lived there 35 years ago...wonder if it is still working?