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. 2016 Dec 28;95(6 Suppl):4-14.
doi: 10.4269/ajtmh.16-0160. Epub 2016 Oct 31.

Implications of Plasmodium vivax Biology for Control, Elimination, and Research

Affiliations

Implications of Plasmodium vivax Biology for Control, Elimination, and Research

Piero L Olliaro et al. Am J Trop Med Hyg. .

Abstract

This paper summarizes our current understanding of the biology of Plasmodium vivax, how it differs from Plasmodium falciparum, and how these differences explain the need for P. vivax-tailored interventions. The article further pinpoints knowledge gaps where investments in research are needed to help identify and develop such specific interventions. The principal obstacles to reduce and eventually eliminate P. vivax reside in 1) its higher vectorial capacity compared with P. falciparum due to its ability to develop at lower temperature and over a shorter sporogonic cycle in the vector, allowing transmission in temperate zones and making it less sensitive to vector control measures that are otherwise effective on P. falciparum; 2) the presence of dormant liver forms (hypnozoites), sustaining multiple relapsing episodes from a single infectious bite that cannot be diagnosed and are not susceptible to any available antimalarial except primaquine, with routine deployment restricted by toxicity; 3) low parasite densities, which are difficult to detect with current diagnostics leading to missed diagnoses and delayed treatments (and protracted transmission), coupled with 4) transmission stages (gametocytes) occurring early in acute infections, before infection is diagnosed.

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Figures

Figure 1.
Figure 1.
Plasmodium vivax cycle and main biological characteristics.
Figure 2.
Figure 2.
Patterns of primary attack and relapse of the principal Plasmodium vivax strains.
Figure 3.
Figure 3.
Schematic representation of the course of a blood infection with time in Plasmodium falciparum (A) and Plasmodium vivax (B). The vertical axis is parasite densities (sexual and asexual forms) in the blood; the horizontal axis is time since infection; both are arbitrary and there are no units. In the absence of treatment, asexual blood parasitaemia is depicted in solid red line and gametocytemia in solid green lines. The bars represent infectivity of gametocytes to mosquitoes. The clinical threshold parasitaemia is shown below the gray area; symptoms tend to occur at lower parasitemias in a P. vivax compared with P. falciparum infection. In P. vivax gametocyte counts are generally one-tenth of the asexual parasite counts. When effective treatment is administered at the point indicated by the vertical arrow, the parasitemia declines as depicted by the broken red lines preventing further gametocytemia. Thus early and effective treatment will, in P. falciparum, abolish gametocytes and infectivity to mosquitoes, whereas in P. vivax transmission has already occurred by the time treatment is administered.

References

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