Diagnosis of Malaria by Magnetic Deposition Microscopy

Abstract

Although malaria contributes to a significant public health burden, malaria diagnosis relies heavily on either non-specific clinical symptoms or blood smear microscopy methods developed in the 1930s. These approaches severely misrepresent the number of infected individuals and the reservoir of parasites in malaria-endemic communities and undermine efforts to control disease. Limitations of conventional microscopy-based diagnosis center on time required to examine slides, time required to attain expertise sufficient to diagnose infection accurately, and attrition from the limited number of existing malaria microscopy experts. Earlier studies described magnetic properties of Plasmodium falciparum but did not refine methods to diagnosis infection by all four human malaria parasite species. Here, following specific technical procedures, we show that it is possible to concentrate all four human malaria parasite species, at least 40-fold, on microscope slides using very inexpensive magnets through an approach termed magnetic deposition microscopy. This approach delivered greater sensitivity than a thick smear preparation while maintaining the clarity of a thin smear to simplify species-specific diagnosis. Because the magnetic force necessary to concentrate parasites on the slide is focused at a precise position relative to the magnet surface, it is possible to examine a specific region of the slide for parasitized cells and avoid the time-consuming process of scanning the entire slide surface. These results provide insight regarding new strategies for performing malaria blood smear microscopy.

Epidemiology and Infectivity of Plasmodium falciparum and Plasmodium vivax Gametocytes in Relation to Malaria Control and Elimination

“…Use of the quantitative buffy coat technique, in which a 55-l blood volume is examined by use of acridine orange-coated capillary tubes (453), increased the prevalence of gametocytes from 4.6% to 19.1% (301). Magnetic deposition microscopy (MDM) is used to concentrate erythrocytic-stage malaria parasites that contain hemozoin by exploiting their paramagnetic characteristics using strong magnetic fields (529). MDM makes it possible to screen a larger blood volume, thereby improving the detection sensitivity compared to that of routine microscopy.…”

Separation of Magnetic Particles Using an Array of Magnets —A Model of a Separation Device for Malaria-Infected Blood Cells

“…One of them is a microfluidic device that is cheap, requires less diagnosis time, uses small amounts of samples, and does not need a skilled technician. (4)(5)(6)(7)(8)(9)(10) Recently, hemozoin, produced by a malaria parasite invading red blood cells, is being considered as an alternative biomarker for malaria diagnosis. Many research studies demonstrated that malaria-infected red blood cells (iRBCs) show magnetic properties distinct from those of healthy red blood cells (hRBCs), as shown in Table 1, and many groups have already utilized this difference for detecting or separating iRBCs in a label-free manner on a high gradient of a magnetic field inside the microfluidic device.…”

“…Many research studies demonstrated that malaria-infected red blood cells (iRBCs) show magnetic properties distinct from those of healthy red blood cells (hRBCs), as shown in Table 1, and many groups have already utilized this difference for detecting or separating iRBCs in a label-free manner on a high gradient of a magnetic field inside the microfluidic device. (4)(5)(6)(7)(8) However, the current design has some limitations, such as being a batch process, having low precision, or causing severe damage to iRBCs. One important issue to be resolved is the significant reduction in the magnitude of the magnetic force with distance from the magnet poles.…”

“…Zimmerman et al demonstrated the new platform utilizing the gap between two different poles of magnets to increase the concentration of infected blood cells, but its operation requires multiple steps. (4) The microfluidic channel combined with a ferromagnetic wire in a microscale, on the other hand, is difficult to operate as well as requiring a highly precise fabrication. (5) To tackle the problem, we employed an array of magnets, as an array can locally generate a high gradient of magnetic field as well as a magnetic force that are comparable to a single magnet pole.…”

Microfluidic Devices for Blood Fractionation

“…For example, several microfluidic devices have been developed for malaria detection, which is one of the severest parasitic blood-borne diseases and most prevalent in the poorer countries. The separation principles are mostly based on intrinsic properties of malaria-infected RBCs (iRBCs) such as dielectric differences [71], paramagnetic affinity [72], and change in stiffness [73,74] to separate or enrich them from blood for diagnostic applications. However, as iRBCs constitute ~0.01-1% in peripheral blood of malaria patients, they are not considered as rare-cell per se and thus excluded in our discussion.…”