thumb|In 1903, David Bruce recognized the tsetse fly as the arthropod vector. The condition has been present in Africa for thousands of years. Because of a lack of travel between Indigenous people, sleeping sickness in humans had been limited to isolated pockets. 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.
thumb|In 1903 David Bruce recognized the tsetse fly as the arthropod vector The condition has been present in Africa for thousands of years Because of a lack of travel between Indigenous people sleeping sickness in humans had been limited to isolated pockets 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