A Way Forward for Culturing Plasmodium vivax

Abstract

Trager and Jensen established a method for culturing Plasmodium falciparum, a breakthrough for malaria research worldwide. Since then, multiple attempts to establish Plasmodium vivax in continuous culture have failed. Unlike P. falciparum, which can invade all aged erythrocytes, P. vivax is restricted to reticulocytes. Thus, a constant supply of reticulocytes is considered critical for continuous P. vivax growth in vitro. A critical question remains why P. vivax selectively invades reticulocytes? What do reticulocytes offer to P. vivax that is not present in mature erythrocytes? One possibility is protection from oxidative stress by glucose-6-phosphate dehydrogenase (G6PD). Here, we also suggest supplements to the media and procedures that may reduce oxidative stress and, as a result, establish a system for the continuous culture of P. vivax.

Keywords: Plasmodium vivax; in vitro; oxidative stress; reticulocytes.

Figure 1:. Schuffner’s dots in P. vivax and P. cynomolgi infected erythrocytes.

A. Illustration shows the P. vivax infected reticulocytes in a ring form with Schuffner’s dots in red as in Geimsa-stained films. Electron microscopy images (B and C) represent P. vivax and P. cynomolgi infected erythrocytes, respectively, showing caveola-vesical complexes (indicated by arrows) which are Schuffner’s dots specific to these two species. Figures in panel B and C are adapted from Aikawa et al. [23] with permission.

Figure 2:. Hypoxia conditions to combat oxidative stress in P. vivax and reticulocytes.

Panel A shows the P. vivax culture maintenance (medium change) in the hood where P. vivax and reticulocytes are exposed to ambient air. The parasites develop from rings, trophozoites to schizonts but fail to invade uninfected fresh reticulocytes and the cycle stops. Panel B shows a hypothetical experiment in which P. vivax culture maintenance (medium change) and growth occurs in a hypoxia chamber at 37°C and low oxygen concentration between 1 to 5 % throughout. The parasites undergo healthy development from rings, trophozoites to schizonts then invade the healthy reticulocytes and the cycle continues.