1. An often fatal, endemic infectious disease of humans and animals in tropical Africa, caused by either of two trypanosomes (Trypanosoma rhodesiense or T. gambiense) transmitted by the tsetse fly and characterized by fever, severe headache, and lymph node swelling in the early stages, followed by extreme weakness, sleepiness, and deep coma. Also called African sleeping sickness.
2. See encephalitis lethargica.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.