Sleeping sickness is transmitted through the bite of an infected tsetse fly. The tsetse fly carries two protozoa, Trypanosoma brucei rhodesiense and Trypanosomoa brucei gambiense, which spread through the bloodstream and can cause swelling of the brain. Symptoms include daytime sleepiness. Treatment options include pentamidine injections for Trypanosomoa brucei gambiense infections, but this medicine is toxic and not recommended for preventing Trypanosoma brucei rhodesiense infections.