Boundary behaviours of Leishmania mexicana: a hydrodynamic simulation study*

The cause of a neglected human tropical disease, the microswimmer Leishmania mexicana exhibits complex surface interactions with the sandfly vector midgut. Previously unstudied, the hydrodynamics of this large-bodied monoflagellate puller may not be deduced from previous studies of low-Reynolds number swimming using the time-reversibility of Stokes flow. Thus we aim to elucidate the boundary behaviours of such a swimmer, and begin by identifying a planar mode of the beating flagellum from digital videomicroscopy. Swimmer behaviour is then studied in detail via the boundary element method, utilising time-averaged phase plane analysis to study virtual Leishmania promastigotes in the presence of a planar boundary. From this analysis we identify a remarkable morphology-dependent mechanism of boundary approach, a potential mechanism driving tip-first epithelial attachment seen in L. mexicana in vivo.