Final answer:
The tsetse fly is responsible for transmitting sleeping sickness to humans and nagana to cattle, caused by the protozoa Trypanosoma brucei.
Step-by-step explanation:
The African fly that causes sleeping sickness in humans and a similar ailment called nagana in cattle is the tsetse fly. This disease in humans, known as Human African Trypanosomiasis (HAT) or African sleeping sickness, is caused by the hemoflagellate Trypanosoma brucei. There are two subspecies that affect humans: Trypanosoma brucei rhodesiense leads to East African trypanosomiasis (EAT), and Trypanosoma brucei gambiense causes West African trypanosomiasis (WAT). The tsetse fly, native to sub-Saharan Africa, transmits the disease through its bite. After the fly bites an infected host, the parasites develop in the gut of the fly and then migrate to the insect's salivary glands, where they can be transmitted to a new host during another blood meal. Sleeping sickness is characterized by symptoms such as severe fatigue, coma, and can result in death if left untreated due to its impact on the central nervous system.