It is found in Central and West African countries (Nigeria, Congo etc.). It is a blood parasite of man and gut parasite of tse-tse flies. It is transmitted from man to man mainly by the blood sucking tse-tse fly, Glossina palpalis. However, Glossina tachinoides also transmits it. It causes Gambian or African sleeping sickness (or trypanosomiasis) in man. It is a fatal disease.
T. gambiense was first reported by Forde in 1901. Sir David Bruce first detected that it is transmitted by tse-tse flies. Trypanosoma occurs in four different forms. These are classified on the basis of the positions of kinetoplast, blepharoplast and the flagellum. These forms are as under:
1. Leishmania (amastigote) : It is the round or oval form. The reduced flagellum remains in the cytoplasm Blepharoplast and kinetoplast are situated in the anterior part.
2. Leptomonad (promastigote): Body is elongated and blepharoplast and kinetoplast are anterior in position. Flagellum is short, unattached and free.
3. Crithidia (epimastigote): Body is elongated. Blepharoplast and kinetoplast are situated in the middle of the body but just anterior to the nucleus. Undulating membrane is not well defined.
4. Trypanosome (trypomastigote) : Body is elongated. Blepharoplast and the kinetoplast are situated at the posterior end. Undulating membrane is well developed.
Out of these four forms trypanosome is the adult stage while other forms represent developmental stages which are formed during the part of its life cycle in the invertebrate host.