The transmission cycle
T.b. gambiense sleeping sickness is transmitted from human to human by the tsetse fly which is the most common form of transmission. As some animals can host the human pathogenic parasite, transmission can occasionally take place directly from animals to humans, which is believed to be one of the causes of the long term maintenance of the disease in endemic areas. However the epidemiological importance of such zoonotic transmission is poorly understood.
T.b. rhodesiense sleeping sickness transmission cycle involves to a great extent domestic and wild animals. Intensified man to man transmission occurs during epidemics. The strong zoonotic character of the T.b. rhodesiense form of the disease substantially complicates surveillance and control issues, requiring action on the fly or on the animals hosting the parasite.
Vertical transmission (mother to child) is very frequent in infected pregnant. Blood transfusion and laboratory infection have been described.