Total parasite biomass but not peripheral parasitaemia is associated with endothelial and haematological perturbations in Plasmodium vivax patients.

João L Silva-Filho,João Ck Dos-Santos,Marcus Vg Lacerda,Carla Judice,Stefanie Cp Lopes,Kannan Venugopal,Diogenes Lima,Matthias Marti,Dario Beraldi,Erich V De Paula,Helder I Nakaya,Fabio Tm Costa

doi:10.7554/elife.71351

Abstract

Plasmodium vivax is the major cause of human malaria in the Americas. How P. vivax infection can lead to poor clinical outcomes, despite low peripheral parasitaemia, remains a matter of intense debate. Estimation of total P. vivax biomass based on circulating markers indicates existence of a predominant parasite population outside of circulation. In this study, we investigate associations between both peripheral and total parasite biomass and host response in vivax malaria. We analysed parasite and host signatures in a cohort of uncomplicated vivax malaria patients from Manaus, Brazil, combining clinical and parasite parameters, multiplexed analysis of host responses, and ex vivo assays. Patterns of clinical features, parasite burden, and host signatures measured in plasma across the patient cohort were highly heterogenous. Further data deconvolution revealed two patient clusters, here termed Vivaxlow and Vivaxhigh. These patient subgroups were defined based on differences in total parasite biomass but not peripheral parasitaemia. Overall Vivaxlow patients clustered with healthy donors and Vivaxhigh patients showed more profound alterations in haematological parameters, endothelial cell (EC) activation, and glycocalyx breakdown and levels of cytokines regulating different haematopoiesis pathways compared to Vivaxlow. Vivaxhigh patients presented more severe thrombocytopenia and lymphopenia, along with enrichment of neutrophils in the peripheral blood and increased neutrophil-to-lymphocyte ratio (NLCR). When patients' signatures were combined, high association of total parasite biomass with a subset of markers of EC activation, thrombocytopenia, and lymphopenia severity was observed. Finally, machine learning models defined a combination of host parameters measured in the circulation that could predict the extent of parasite infection outside of circulation. Altogether, our data show that total parasite biomass is a better predictor of perturbations in host homeostasis in P. vivax patients than peripheral parasitaemia. This supports the emerging paradigm of a P. vivax tissue reservoir, particularly in the haematopoietic niche of bone marrow and spleen.

Highlights

Malaria remains a heavy burden across endemic regions worldwide
Our analysis revealed an association between alterations in host homeostasis, including endothelial cell (EC) activation, damage and haematological disturbances, such as thrombocytopenia, lymphopenia and increased neutrophils turnover, with total parasite biomass but not peripheral parasitaemia
Blood was collected at enrolment for determination of haematological parameters, peripheral parasitaemia by Giemsa staining of blood smears and PCR to determine genome copy numbers

Summary

Introduction

Malaria remains a heavy burden across endemic regions worldwide. In 2018 P. vivax infection accounted for 41% of all malaria cases outside of Sub-Saharan Africa, with a total of 6.5 million cases and more than 2 billion people in 90 countries at risk 1. There are concerns that P. vivax elimination will be significantly more difficult than P. falciparum, as the current measures for malaria control are less effective for P. vivax than for P. falciparum, with the elimination of the former presenting a major challenge in areas that successfully reduced P. falciparum burden This persistence is due to some unique biological features complicating treatment and elimination, including low peripheral parasitaemia and presence of dormant liver stages (hypnozoites) which relapse weeks or months after blood infection has been cleared. Our analysis revealed an association between alterations in host homeostasis, including EC activation, damage and haematological disturbances, such as thrombocytopenia, lymphopenia and increased neutrophils turnover, with total parasite biomass but not peripheral parasitaemia These findings are in line with the emerging paradigm of a clinically relevant parasite reservoir outside of circulation and merit systematic investigations of this reservoir in vivax malaria

Results

336 Discussion

Materials and Methods

805 References