Ford and Dutton (1902) were first to report that Trypanosoma was a human parasite and also the causative of ‘Gambia’ fever: Kleine (1909) asserted that tse-tse fly (Glossina) was the intermediate host in the life history of Trypanosoma.
Trypanosoma belongs to the Order Kinetoplastida which comprises relatively simple forms possessing 1-2 flagella provided with a few accessory kinetic structures. Trypanosoma and its relatives constitute a closely knit family of pleomorphic parasites which are of great medical and economic importance. Members of the genus are found in all the classes of vertebrates but are pathogenic only to man and domestic mammals, probably representing recently acquired hosts. The cause of their extreme harmfulness to man and domestic mammals is obscure but may consist in the liberation of toxins. The pathogenic trypanosomes are confined to the tropical countries. They are transmitted from one host to another by blood sucking invertebrates such as insects, mites, ticks and leeches, in whose intestine they undergo a definite cycle of development, requiring a number of days, before they become again infective to vertebrates.
There are two species of Trypanosoma found in man. The African human trypanosomiasis, known as sleeping sickness, is caused by T. brucei gambiense and T. brucei rhodesiense. The first subspecies is confined to the central and West Africa particularly in Congo and Nigeria. The second subspecies in Rhodesia. The victors for these trypanosomes are species of blood sucking tsetse fly-Glossina palpalis or Glossina tachenoide. Another species is Trypanosoma cruzi, it is found in South and Central Africa in man and a diversity of mammals, between which it is transmitted by blood sucking bugs Rhodnius or Triatoma megista. The following description is based on the biology of T. brucei gambiense.