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Background    Plasmodium vivax  can cause severe malaria. The total parasite biomass during infections is correlated with the severity of disease but not necessarily quantified accurately by microscopy. This finding has raised the question whether there could be sub-populations of parasites that are not observed in peripheral blood smears but continue to contribute to the increase in parasite numbers that drive pathogenesis. Non-human primate infection models utilizing the closely related simian malaria parasite  Plasmodium cynomolgi  hold the potential for quantifying the magnitude of possibly unobserved infected red blood cell (iRBC) populations and determining how the presence of this hidden reservoir correlates with disease severity.    Methods  Time series data tracking the longitudinal development of parasitaemia in five  Macaca mulatta  infected with  P. cynomolgi  were used to design a computational model quantifying iRBCs that circulate in the blood versus those that are not detectable and are termed here as ‘concealed’. This terminology is proposed to distinguish such observations from the deep vascular and widespread ‘sequestration’ of  Plasmodium falciparum  iRBCs, which is governed by distinctly different molecular mechanisms.    Results  The computational model presented here clearly demonstrates that the observed growth data of iRBC populations are not consistent with the known biology and blood-stage cycle of  P. cynomolgi . However, the discrepancies can be resolved when a sub-population of concealed iRBCs is taken into account. The model suggests that the early growth of a hidden parasite sub-population has the potential to drive disease. As an alternative, the data could be explained by the sequential release of merozoites from the liver over a number of days, but this scenario seems less likely.    Conclusions  Concealment of a non-circulating iRBC sub-population during  P. cynomolgi  infection of  M. mulatta  is an important aspect of this successful host–pathogen relationship. The data also support the likelihood that a sub-population of iRBCs of  P. vivax  has a comparable means to become withdrawn from the peripheral circulation. This inference has implications for understanding vivax biology and pathogenesis and stresses the importance of considering a concealed parasite reservoir with regard to vivax epidemiology and the quantification and treatment of  P. vivax  infections.    Electronic supplementary material  The online version of this article (doi:10.1186/s12936-017-2008-4) contains supplementary material, which is available to authorized users.

A model of Plasmodium vivax concealment based on Plasmodium cynomolgi infections in Macaca mulatta