Discussion

Parasite life cycles are traditionally depicted as static pictures of different life-cycle stages in various tissues. These depictions overlook the question of how parasites home in on these tissues and then move from one to the next, particularly when they need to cross barriers. Trypanosoma brucei is an extracellular parasite that sequentially occupies different tissues in the alimentary tract of its tsetse fly host. Our recent work on social motility, the collective migration of procyclic (insect midgut) forms on agarose surfaces, has provided insights into how the parasites both condition and sense their environment. In addition to explaining the self-organising properties of trypanosome communities on plates, we have shown that the same sensors, which are components of the cyclic AMP signalling pathway, are required for efficient colonisation of the tsetse midgut and penetration of the peritrophic matrix.