Mechanical Evidence of the impossibility of directed motion of Trypanosoma cruzi towards preferred organs in the Human Body, a simulation 2D model within a laminar flow

TL;DR

This work presents a 2D elastic representation of Trypanosoma cruzi embedded in a Dissipative Particle Dynamics fluid to test whether parasite deformation can direct motion toward organs in blood. By coupling a five-discretization triangular mesh parasite to a 2D DPD flow and simulating both deforming and non-deforming states, the authors show self-propulsion in still fluid but a lack of directed transport in moving fluid, with displacement mainly governed by flow drag at high Reynolds numbers. Key findings indicate the parasite cannot achieve tropism through deformation alone in this 2D setup, implying that long-range in vivo displacement is primarily due to blood flow rather than autonomous motility, and highlight the need for 3D modeling and an explicit flagellum to capture more realistic dynamics. The work provides a computationally tractable framework to test hypotheses about parasite motility and offers a foundation for future, more detailed simulations of host–parasite transport.

Abstract

The movement of the infective form of the T. Cruzi parasite within the human blood is not completely understood. Video microscopy observations confirm forward motility of the protozoa and relate it to the deformation of the body, nonetheless there are open questions relating the deformation of the protozoan with its motion in blood, for which a computational model would be very helpful. Hereby we introduce a simple computational 2D model to test whether it is mechanistically possible for the parasite to direct its movement through the blood stream towards preferred organs in the bloodstream. We model the infective form of the T. cruzi, the causative agent of Chagas disease; by means of a network of harmonic springs that represents its body, without explicitly modeling the flagellum. We coupled this with a particle model of a laminar fluid flow, which we implemented using the Dissipative Particles Dynamics method. Our parasite model swims on still fluid, its center of mass displacement being larger than the end to end deformation. Laminar flow dragged the model parasite of the order of 5 $μm$; having minor effects on its structure. The parasite model does not exhibit directed motion in a moving fluid, suggesting that the large-scale displacement of the real parasite is not attributable to its own motility but is instead caused by it being dragged by the flow. We highlight two potential improvements for the model: incorporating the capacity to describe 3D motion and including a specific depiction of the flagellum.

Figures (14)

• Figure 1: Collision stage. Momentum vector pointing out of the structure.
• Figure 2: Collision stage. Group of fluid particles approaching to cell membrane.
• Figure 3: T. Cruzi 2D model: thin straight lines represent internal springs (blue), thick straight lines the surface of the parasite (green), and thick disks the nodes (yellow). Thin disks represent the DPD particles (red). In this case the simulation box has width of $45 \mu m$ and a depth of 12 $\mu m$.
• Figure 4: Center of mass position of the T.Cruzi as a function of time for different values of the random number generator seed: thick continuous (blue), first seed; dashed (yellow), second seed; dash dot (green), third seed; thin continuous (black), fourth seed; dotted (red), fifth seed.(Color online). Distances in $\mu m$.
• Figure 5: Center of mass position of the T. Cruzi as a function of time for different DPD particle densities: thick smooth continuous (blue), $N_{DPD}=900$; dashed (yellow), $N_{DPD}=1800$; dot dashed (green), $N_{DPD}=2700$.(Color online). Distances in $\mu m$.