A Two-Dimensional Numerical Investigation of Transport of Malaria-Infected Red Blood Cells in Stenotic Microchannels

A Lab-On-chip Tool for Rapid, Quantitative, and Stage-selective Diagnosis of Malaria

Malaria remains the most important mosquito-borne infectious disease worldwide, with 229 million new cases and 409.000 deaths in 2019. The infection is caused by a protozoan parasite which attacks red blood cells by feeding on hemoglobin and transforming it into hemozoin. Despite the WHO recommendation of prompt malaria diagnosis, the quality of microscopy-based diagnosis is frequently inadequate while rapid diagnostic tests based on antigens are not quantitative and still affected by non-negligible false negative/positive results. PCR-based methods are highly performant but still not widely used in endemic areas. Here, a diagnostic tool (TMek), based on the paramagnetic properties of hemozoin nanocrystals in infected red blood cells (i-RBCs), is reported on. Exploiting the competition between gravity and magnetic forces, i-RBCs in a whole blood specimen are sorted and electrically detected in a microchip. The amplitude and time evolution of the electrical signal allow for the quantification of i-RBCs (in the range 10-105 i-RBC µL-1) and the distinction of the infection stage. A preliminary validation study on 75 patients with clinical suspect of malaria shows on-field operability, without false negative and a few false positive results. These findings indicate the potential of TMek as a quantitative, stage-selective, rapid test for malaria.

Hemozoin is a potential threat in cerebral malaria pathology through the induction of RBC-EC cytoadherence

Cerebral malaria is an outcome of multifaceted and complicated condition. Cytoadherence is one critical factor in cerebral malaria pathology as high order cytoadherence complexes result in vascular congestion and cell apoptosis. Morphological abnormalities in uninfected RBCs can be a contributing factor to aggravate cytoadherence. Malaria pigment hemozoin is a potential bioactive molecule and the role of this pigment in cerebral malaria pathology is not completely understood. To understand this, primarily we investigated the impact of hemozoin pigment on uninfected RBCs. Secondarily, we investigated the role of this pigment in formation of endothelial cells-RBCs (EC-RBC) cytoadherence complex. We first observed that a dose dependent hemozoin exposure to uninfected RBCs induced structural abnormalities. Differential counting of these abnormal RBCs indicated population of acanthocytes, spherocytes and microcytes. The formation of abnormal RBCs was observed with phosphatidylserine externalization. Lipid peroxidation, reduced glutathione and reactive oxygen species (ROS) levels indicated an increase in hemozoin exposure mediated oxidative stress. Our in-vitro cytoadherence assay indicated formation of endothelial EC-RBC cytoadherence complex. The dose dependent hemozoin exposure to uninfected RBCs resulted in oxidative stress mediated high order cytoadherence complex formation. This effect was reversed in presence of antioxidant molecules. The inhibitory effect of antioxidant molecules indicates that oxidative stress can be a regulatory factor to control cerebral malaria pathology. Being the first report to highlight the impact of malaria pigment hemozoin on uninfected RBCs, this study brings attention to the role of abnormal RBCs in worsening of cerebral malaria pathology.

Local Hematocrit Fluctuation Induced by Malaria-Infected Red Blood Cells and Its Effect on Microflow

We investigate numerically the microscale blood flow in which red blood cells (RBCs) are partially infected by Plasmodium falciparum, the malaria parasite. The infected RBCs are modeled as more rigid cells with less deformability than healthy ones. Our study illustrates that, in a 10 μm microvessel in low-hematocrit conditions (18% and 27%), the Plasmodium falciparum-infected red blood cells (Pf-IRBCs) and healthy ones first form a train of cells. Because of the slow moving of the Pf-IRBCs, the local hematocrit (H_ct) near the Pf-IRBCs is then increased, to approximately 40% or even higher values. This increase of the local hematocrit is temporary and is kept for a longer length of time because of the long RBC train formed in 27%-H_ct condition. Similar hematocrit elevation at the downstream region with 45%-H_ct in the same 10 μm microvessel is also observed with the cells randomly located. In 20 μm microvessels with 45%-H_ct, the Pf-IRBCs slow down the velocity of the healthy red blood cells (HRBCs) around them and then locally elevate the volume fraction and result in the accumulation of the RBCs at the center of the vessels, thus leaving a thicker cell free layer (CFL) near the vessel wall than normal. Variation of wall shear stress (WSS) is caused by the fluctuation of local H_ct and the distance between the wall and the RBCs. Moreover, in high-hematocrit condition (45%), malaria-infected cells have a tendency to migrate to the edge of the aggregates which is due to the uninterrupted hydrodynamic interaction between the HRBCs and Pf-IRBC. Our results suggest that the existence of Pf-IRBCs is a nonnegligible factor for the fluctuation of hematocrit and WSS and also contributes to the increase of CFL of pathological blood flow in microvessels. The numerical approach presented has the potential to be utilized to RBC disorders and other hematologic diseases.

Numerical Simulations of the Motion and Deformation of Three RBCs during Poiseuille Flow through a Constricted Vessel Using IB-LBM

The immersed boundary-lattice Boltzmann method (IB-LBM) was used to examine the motion and deformation of three elastic red blood cells (RBCs) during Poiseuille flow through constricted microchannels. The objective was to determine the effects of the degree of constriction and the Reynolds (Re) number of the flow on the physical characteristics of the RBCs. It was found that, with decreasing constriction ratio, the RBCs experienced greater forced deformation as they squeezed through the constriction area compared to at other parts of the microchannel. It was also observed that a longer time was required for the RBCs to squeeze through a narrower constriction. The RBCs subsequently regained a stable shape and gradually migrated toward the centerline of the flow beyond the constriction area. However, a sick RBC was observed to be incapable of passing through a constricted vessel with a constriction ratio ≤1/3 for Re numbers below 0.40.