1 LSTM, UK
DiscussionThe tsetse peritrophic matrix (PM) is a chitinous structure that surrounds the bloodmeal and forms a physical barrier for ingested pathogens, like trypanosomes. To establish an infection and avoid harmful factors present in the bloodmeal, sub-species of Trypanosoma brucei colonise the tsetse ectoperitrophic space (ES), which is located between the PM and the gut epithelium. Although unproven, and despite the fact that T. brucei parasites do not express chitinases, it is generally accepted that after stumpy trypanosomes differentiate into early procyclic cells within the anterior midgut, the parasites reach the tsetse ES by direct penetration of the PM. Here we re-visited this event by employing several microscopy techniques, including confocal and serial block face-scanning electron microscopy that allowed 3D-reconstructions of trypanosome-infected tissues. We found no evidence supporting direct crossing of the tsetse PM by procyclic trypanosomes. Instead, early procyclic trypanosomes first colonise the proventriculus (place of PM synthesis), where they can either reach the ES or become trapped in pockets between PM layers, which move along the entire gut as the PM gets remodeled.