Parasite Host (IMAGE) UT Southwestern Medical Center Caption Trypanosoma brucei, the parasite that causes the deadly sleeping sickness, is shown in brown feeding on the host tissue. Scientists have determined sleeping sickness is actually a circadian rhythm disorder caused by the acceleration of biological clocks controlling a range of vital functions besides sleep. Credit University of Lisbon Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.