Studies on the behaviour of Trypanosoma evansi in tsetse-flies with special reference to its phylogeny

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Abstract
In view of the morphological similarity of T. evansi and T. brucei, including the sporadic occurrence of marked polymorphism in the first-named species, the hypothesis is advanced that T. evansi may have originated from T. brucei, by the introduction of the last-named species into localities free of Glossina and its subsequent propagation by direct passages.The possibility of contact between the mammalian host of T. evansi, on the one hand, and Glossina and tsetse-borne trypanosomiases, on the other, is shown to exist in the Anglo-Egyptian Sudan, thus pointing to the source from which T. evansi in that country may have originated and providing circumstantial evidence in support of the hypothesis.Attempts were made to discover whether T. evansi is capable of developing in Glossina. A total of 568 flies were fed on infected mice and examined at periods from 6 hr. to a fortnight following the infective feed. The results were entirely negative: not only is the trypanosome incapable of establishing an infection in the fly, but the majority of flagellates perish and are digested during the first hours after ingestion by the insect.The behaviour of T. evansi in tsetse is shown to be similar to that of non-transmissible strains of trypanosomes of the Brucei group after prolonged maintenance by direct passages in the mammalian hosts, and is therefore also in keeping with the hypothesis.

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