African Trypanosomiasis or Sleeping Sickness is a parasitic disease transmitted by the tsetse fly. It is endemic in much of Africa and affects both cattle and humans. The prevalence of the disease and the ease of its spread often affects the ability of either humans or cattle to inhabit a given area.
The primary symptom of the disease is hypersomnia or excessive sleep, although the disease can also cause insomnia. In all cases, the disease greatly affects brain function and eventually causes severe neurological symptoms before almost inevitably resulting in death.
The best treatment is preventative, essentially staying out of areas where the fly is known to inhabit, or treating areas to prevent the spread of the flies. Otherwise, treatment is both expensive and dangerous. A person without the disease who is treated for it will almost certainly die from the treatment, and a good proportion of patients with the disease will also respond poorly to treatment.
See also Chagas Disease, a disease enemic to the Americas which is caused by a similar parasite, but has somewhat different symptoms and is easier to treat.