Illustration of metacyclic trypomastigote. Trypanosomes are protozoan parasites that cause Human African Trypanosomiasis (HAT), also known as sleeping sickness. The disease is spread by the tse-tse fly. 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. The identical-looking trypomastigotes of T. cruzi are found in the blood of people with Chagas' disease (American trypanosomiasis).