Studies on Trypanosoma (nannomonas) congolense. I. On the morphological appearance of the parasite in the mouse.

The pleomorphism of bloodstream Trypanosoma (Nannomonas) congolense was studied during the course of the first parasitaemic wave in mice using cloned and uncloned derivatives of three recent field isolates. The different morphological types were identified using the criteria described by Godfrey (1960). It was found that at any point of parasitaemia there were several morphological types of the parasite present, ranging from short to long forms. In the rising phase of parasitaemia, the short forms predominated, while at peak parasitaemia the parasites were highly pleomorphic, with significant proportions of short and "intermediate" forms although the long forms predominated. Pleomorphism was observed both in normal and in lethally irradiated (900 R) mice, even when the infection was initiated using a single organism. Such pleomorphism may result from physiological differences between the different forms of this parasite since these morphological types of T. congolense also differed in their ability to infect a new mammalian host.