*Obligatory huffing and puffing* Taking out the Tsetse fly itself takes out humanity as we know it, without ASB intervention.
Assuming you keep with these route, however, soon after horses are introduced to Egypt as per OTL they will be traded southward. Eventually, southern pastoralists will adapt them and will ride southward with them. With the horse, and with more widespread livestock and a larger population, sub-Saharan Africa can have far more trade with the Mediterranean and becomes far more advanced than OTL. The larger interaction of people from the southern and Mediterannean ends of the Nile creates new cultures on both sides of the exchange unlike anything that exists IOTL. Examples could include Greek cults dedicated to Zeus as Ngai, God of the Mountain, Kikuyu adopting hieroglyphics and creating a highland kingdom, and mounted Dinka conquering Kush, Egypt, and the Levant. Really, this does a lot of crazy stuff.
An alternative to having the Tsetse fly never evolved, I thought, would be the appearance of a virus that attacks the organisms that cause sleeping sickness sometime after the end of the last ice age. The organisms that survive the onslaught of this virus change so that they cannot alter their cells as in OTL, and therefore are not able to fool the immune system of humans or other mammals. Sleeping sickness is still a problem, but after some generations of exposure humans, cattle, and horses develop some immunity.