From solitary swimmers to swarms and back: trypanosomes on their journey through the tsetse fly

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African trypanosomes cause deadly disease in human and cattle. The unicellular blood parasites populate the body fluids of their mammalian hosts, as well as the digestive tract of the disease transmitting insect, the infamous tsetse fly. Trypanosomes are incessant microswimmers, and we have characterized their motion behaviour in human blood and tissue spaces. This project aims at understanding how swimming contributes to the surprisingly long journey of the parasites through the fly, which takes several weeks. We have detailed the cell architectures and swimming performances of eight distinct trypanosome life cycle stages in the tsetse fly and found remarkably different behaviours. While some trypanosome forms are solitary swimmers and actually reveal self-avoidance, others form large swarms and show marked collective behaviour. Some trypanosome stages swim along walls and navigate within the bizarre geometries of the tsetse gut. We have measured the microenvironments the tsetse fly gut and have traced the trypanosomes in living flies using genetic engineering and advanced imaging methods, including light sheet fluorescence microscopy. We now want to challenge our findings by constructing true nature-inspired microfluidics devices that closely mimic the biophysical environments within the tsetse fly, including confinement, flows and viscosities. With this we want to unravel the distinct abilities of different trypanosome stages for near surface swimming, as well as (collective) motion in confinement. The high-resolution data will be interpreted by numerical modelling and computer simulations, and should provide new insights into the low Reynolds number world of flagellate microswimmers.