Figure 9

T. congolense life cycle stages. Representative life cycle stages are shown in their respective locations in the mammalian or tsetse hosts. Bloodstream forms taken up by the fly (arrow) differentiate to procyclics in the fly midgut and grow in length. In the proventriculus the procyclics cease division and become uniform in size and shape. These trypomastigotes migrate to the cibarium and proboscis, where they differentiate to epimastigotes; some of these forms have extremely long or truncated posterior ends as shown in these examples. The infective metacyclics are very small and do not divide. The exact sequence of events between proventricular trypomastigotes arriving in the proboscis/cibarium and production of metacyclics is uncertain, and whether there are gradual or abrupt transitions between stages remains to be elucidated.