Intraerythrocytic 'gametocytes' of <i>Babesia microti</i> and their maturation in ticks

Abstract

The electron microscopic study of several strains of Babesia microti provided evidence that this parasite has two types of organisms in the intraerythrocytic stage. In one, the trophozoites undergo differentiation and reproduce by formation of merozoites. In the other no differentiation or reproduction occurs and the parasites acquire an unusual shape. A hypothesis was put forward that the latter organisms might be gametocytes. This term has been used tentatively throughout this paper. An examination of ticks fed on hamsters' blood infected with B. microti has shown that parasites emerging from hemolyzed erythrocytes closely resemble the intraerythrocytic gametocytes in their shape. A reorganization and differentiation of the cytoplasm expressed in the appearance of new structures occurs. Among them the most striking is a complex organelle that looks like an arrowhead. Several arrowheads are found in a single gametocyte, each marking an incipient gamete. Most gametes are equipped with an arrowhead organelle, a tail, microtubules, and a cytostome. Occasionally a close apposition of two gametes and cytoplasmic fusion between the two organisms was found but it is not excluded that this might represent division. The use of the terms 'gametocyte' and 'gamete' is not yet fully justified. More evidence is needed.