The Differentiation of the Polymorphic Trypanosomes

Abstract

The relationship of the polymorphic trypanosomes, T. gambiense, T. rhodesiense and T. brucei, has been a controversial subject for many years. Owing to the absence of any more definite morphological difference, the discussion has centred round the occurrence of posterior-nuclear forms and such biological characters as infectivity to man, the type of disease produced in man and in small laboratory animals, the susceptibility of the trypanosomes to normal human serum and to arsenical drugs, the red-cell adhesion test, etc. Lester (1933) examined a number of Nigerian strains of T. gambiense and stated that 'The writer believes with Kleine that the two trypanosomes [i.e., T. rhodesiense and T. gambiense] are identical. The trypanosome described as T. rhodesiense is nothing more nor less than a virulent strain of the ordinary human trypanosome T. gambiense. Kinghorn and Yorke (1913), Bruce et al. (1914), Wenyon (1926), Yorke, Adams and Murgatroyd (1930) and Duke (1935) maintained that T. rhodesiense was the same as T. brucei, being merely a strain of the latter which had become established in man, while the German workers (Kleine, Taute, Huber, Beck, quoted by Wenyon, 1926) maintained that they were distinct species. Fairbairn and Burtt (1946) found that a strain of T. rhodesiense, cyclically passaged by Glossina morsitans through sheep for 101 years, had acquired gambiense characteristics; and, while they did not express an opinion on the relationship of T. rhodesiense to T. gambiense, they strongly supported the view that T. rhodesiense and T. brucei were distinct, and not convertible into one another. Van Hoof, Henrard and Peel (1944) considered that they could distinguish T. gambiense from the brucei-rhodesiense group by the distribution, relative number and shape of the trypanosomes developing in the salivary glands of G. palpalis; but such factors are no more exact than the biological characters previously used.