This changed after Arab slave traders entered central Africa from the east, following the Congo River, bringing parasites along. Gambian sleeping sickness travelled up the Congo River, and then further east.An Arab writer of the 14th century left the following description in the case of a sultan of the Mali Kingdom: "His end was to be overtaken by the sleeping sickness (illat an-nawm) which is a disease that frequently befalls the inhabitants of these countries especially their chieftains. Sleep overtakes one of them in such a manner that it is hardly possible to awake him. "The British naval surgeon John Atkins described the disease on his return from West Africa in 1734:
The Sleepy Distemper (common among the Negroes) gives no other previous Notice, than a want of Appetite 2 or 3 days before; their sleeps are sound, and Sense and Feeling very little; for pulling, drubbing or whipping will scarce stir up Sense and Power enough to move; and the Moment you cease beating the smart is forgot, and down they fall again into a state of Insensibility, drivling constantly from the Mouth as in deep salivation; breathe slowly, but not unequally nor snort. Young people are more subject to it than the old; and the Judgement generally pronounced is Death, the Prognostik seldom failing.
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species Trypanosoma brucei. Humans are infected by two types, Trypanosoma brucei gambiense (TbG) and Trypanosoma brucei rhodesiense (TbR). TbG causes over 98% of reported cases. Both are usually transmitted by the bite of an infected tsetse fly and are most common in rural areas.Initially, the first stage of the disease is characterized by fevers, headaches, itchiness, and joint pains, beginning one to three weeks after the bite. Weeks to months later, the second stage begins with confusion, poor coordination, numbness, and trouble sleeping. Diagnosis is by finding the parasite in a blood smear or in the fluid of a lymph node. A lumbar puncture is often needed to tell the difference between first- and second-stage disease. If the disease is not treated quickly it can lead to death. Prevention of severe disease involves screening the at-risk population with blood tests for TbG. Treatment is easier when the disease is detected early and before neurological symptoms occur. Treatment of the first stage has been with the medications pentamidine or suramin. Treatment of the second stage has involved eflornithine or a combination of nifurtimox and eflornithine for TbG. Fexinidazole is a more recent treatment that can be taken by mouth, for either  stages of TbG. While melarsoprol works for both types, it is typically only used for TbR, due to serious side effects.