Illustration of lifecycle of Human African Trypanosomiasis (HAT), also known as sleeping sickness. Trypanosome protozoans are the cause of sleeping sickness (African trypanosomiasis). It is a vector-borne parasite transmitted by bloodsucking tsetse flies (Glossina sp.). The trypomastigote, lives in the bloodstream of the human host, reproducing asexually. It causes a recurring fever, enlarged lymph nodes, joint pain, weight loss and insomnia. Without drug treatment, the disease is usually fatal.