Over time, the parasites invade the central nervous system. The disease causes sleep disorders, mental confusion, personality changes, speech problems, seizures and coma. If left untreated, sleeping sickness kills.
The World Health Organization estimates that about sixty thousand people are currently infected with the disease. It develops in two different forms. Trypanosoma gambiense is responsible for ninety percent of the reported cases of sleeping sickness. People infected with this form may develop the disease over many years without any major symptoms. The disease develops more quickly over a few weeks or months in people infected with trypanosoma rhodesiense.