Geometrical model for malaria parasite migration in structured environments

Malaria is transmitted to vertebrates via a mosquito bite, during which rodlike and crescent-shaped parasites, called sporozoites, are injected into the skin of the host. Searching for a blood capillary to penetrate, sporozoites move quickly in locally helical trajectories, that are frequently perturbed by interactions with the extracellular environment. Here we present a theoretical analysis of the active motility of sporozoites in a structured environment. The sporozoite is modelled as a self-propelled rod with spontaneous curvature and bending rigidity. It interacts with hard obstacles through collision rules inferred from experimental observation of two-dimensional sporozoite movement in pillar arrays. Our model shows that complex motion patterns arise from the geometrical shape of the parasite and that its mechanical flexibility is crucial for stable migration patterns. Extending the model to three dimensions reveals that a bent and twisted rod can associate to cylindrical obstacles in a manner reminiscent of the association of sporozoites to blood capillaries, supporting the notion of a prominent role of cell shape during malaria transmission.