Geographical Distribution.—The disease exists on the West Coast of Africa, from Senegal to Mossamedes. It is also present in the Congo basin and particularly in Uganda. The more virulent form is found in Rhodesia.
Etiology and Epidemiology
Etiology.—The African trypanosomiases follow infection with two species of trypanosomes; the more virulent type of the disease, occurring in South Central Africa, being due to Trypanosoma rhodesiense, transmitted by Glossina morsitans and that of less severe type, but of more general distribution, being due to T. gambiense and transmitted by Glossina palpalis. The very important Trypanosoma brucei, which is the devastating agent in the African horse, dog and cattle disease, nagana, is also transmitted by Glossina morsitans and there exists the opinion that this trypanosome is identical with T. rhodesiense.
Macfie has reported a new trypanosome, T. nigeriense, from young persons in Nigeria. It is said to be less virulent than T. gambiense, and to be transmitted by Glossina tachinoides.
Fig. 26.—Trypanosoma gambiense (slide presented by Professor F. G. Novy) (From Todd.)
Bruce considers T. nigeriense as being T. gambiense. Macfie noted many short stumpy forms in animals inoculated with T. nigeriense.
These trypanosomes are blood flagellates and are typical of the Binucleata in possessing two chromatin-staining areas, the larger and more centrally situated mass being the tropho or macronucleus and the smaller, but more deeply staining one, the kineto or micronucleus (Blepharoplast). Trypanosomes have a fusiform or fish-shaped body which stains blue. Near the less pointed, nonflagellated end, usually called the posterior end, is the deeply stained blepharoplast. Adjoining this is a vacuole and, taking origin from this part of the trypanosome, is the flagellum. This borders an undulating membrane attached to the body and then, carried along to the other extremity, projects free as a long, whip-like flagellum.
In fresh preparations the body of the trypanosome progresses in the direction of its flagellated end, although occasionally it will be observed to move in the opposite direction.
Some trypanosomes show granules at certain stages and it has been observed that the extrusion of these granules precedes disintegration of the trypanosome. It has been suggested that such granules might be infective, explaining the infectivity of blood from which trypanosomes were absent. In the separation of trypanosomes into groups and species Bruce relies upon morphology, action on animals, and manner of development in the tsetse fly. He does not consider serum diagnosis and cross inoculation methods as reliable for differentiation. The human trypanosomes are polymorphic.