It is caused by infection with protozoan parasites belonging to the genus Trypanosoma. They are transmitted to humans by tsetse fly (Glossina genus) bites which have acquired their infection from human beings or from animals harbouring human pathogenic parasites.

Why does Trypanosoma cause sleep sickness?

This overview discusses that the causative agents, the parasites Trypanosoma brucei, target circumventricular organs in the brain, causing inflammatory responses in hypothalamic structures that may lead to dysfunctions in the circadian-timing and sleep-regulatory systems.

How sleeping sickness is caused?

Sleeping sickness is caused by two types of parasites Trypanosoma brucei rhodesiense and Trypanosomoa brucei gambiense. T b rhodesiense causes the more severe form of the illness. Tsetse flies carry the infection. When an infected fly bites you, the infection spreads through your bloodstream.