Infectious diseases other than COVID-19 caused by viruses, bacteria, fungi and parasites kill over 17 million people a year, and this burden is aggravated by asymptomatic transmission. Parasitic diseases are a major public health threat for billions of people worldwide. About 400 parasite species are estimated to infect humans, of which around 90 are responsible for significant morbidity and mortality. Unfortunately, they are mainly endemic to poor regions and are largely neglected.

Plasmodium vivax, with the majority of cases being in Asia and the Americas, and accounting for 7 million annual clinical cases, with over 2.5 billion people living under risk of infection and an estimated global economic burden of 1-4€ billion.

Of relevance, in low-endemic countries that have been targeting vivax malaria for elimination, an increasing number of asymptomatic infections capable of transmitting to mosquitoes are being reported. In fact, during chronic infections, it has been estimated that nearly 70-90% of P. vivax infections are sub-microscopic and asymptomatic. Thus, the global burden of this species is certainly underestimated.

Moreover, experts agree that P. vivax will be the last human malaria parasite species to be eliminated due to its distinctive biology, including:

• Presently undetectable dormant parasites in the liver, called hypnozoites, which upon reactivation cause clinical relapses maintaining transmission.
• A predominant if not exclusive tropism for reticulocytes which has hampered the development of a continuous in vitro culture system.
• Appearance of gametocytes before the onset of clinical symptoms, thus transmitting to mosquitoes before treatment.
• Up-to 98% of the total parasite biomass during chronic asymptomatic infections are cryptic and predominantly found in the spleen with a small percentage also found in the bone marrow.

The severity of vivax malaria is now well recognized despite low peripheral blood parasitemia. However, the underlying pathogenic mechanisms of vivax malaria remain largely unresolved. Thus, elimination of P. vivax needs renewed emphasis on understanding the biology and pathogenesis of this neglected infectious disease.

The importance of exosomes in vivax malaria

Extracellular vesicles are key players implicated in intercellular communication without direct cellular contact. EVs are small membrane-bound vesicles that are generally classified as two major types, exosomes and microvesicles, based on their size, biogenesis and composition. Exosomes are 30-120 nm EVs of endocytic origin secreted by all cells and are present in virtually all-biological fluids. These nanovesicles initially described from reticulocytes, the host cell of P. vivax, are currently recognized by their remarkable role in intercellular communication in normal and pathological conditions, including parasitic diseases.

However, a direct link of circulating EVs from natural human malaria parasite infections and mechanistic insights into pathology had yet to be realized. While researching the physiological roles of EVs in vivo, we isolated and characterized EVs directly from plasma of P. vivax patients and demonstrated that they specifically signaled human spleen fibroblasts, facilitating parasite cytoadherence. With these discoveries in hand, next, we need to define precise and accurate information on the cells, ligand receptors and signaling pathways inside the complex in vivo environment of the host tissues during natural infection.

The overarching hypothesis of our laboratory is to demonstrate that EVs, specifically reticulocyte-derived exosomes, from P. vivax infections mediate bone marrow defects on erythropoiesis and spleen extramedullary erythropoiesis facilitating cryptic infections likely responsible for asymptomatic transmission. Moreover, that EVs will discover new antigens for vaccination and biomarkers of asymptomatic infections in parasitic diseases.

Goals

The Plasmodium vivax and Exosome Research Group is dedicated to the studies of the human malaria caused by Plasmodium vivax and of Extracellular Vesicles as new intercellular communicators, vaccines and diagnostics tools in malaria and other neglected tropical diseases.

Our research focuses on both fundamental and translational aspects to understand host-parasite interactions with the ultimate goal of contributing to the control and eventual elimination of poverty-related diseases.

Lines of Research

• Circulating extracellular vesicles from natural infections as new intercellular communicators in malaria.
• Role of the spleen and the bone marrow during vivax infections.
• Use of OMICs approaches and implementation of P. knowlesi, humanized mouse models and organs-on-a-chip to study P. vivax.
• Discovery of new biomarkers of asymptomatic infections in parasitic diseases associated with circulating EVs and development of POC devices for their validation.

Recent Publications

• Guidelines for the purification and characterization of extracellular vesicles of parasites Fernandez-Becerra C, Xander P,  Alfandari D, Dong G, Aparici-Herraiz I, et al., 2023, "Guidelines for the purification and characterization of extracellular vesicles of parasites", Journal of Extracellular biology, 2, 10. https://doi.org/10.1002/jex2.117
• Gualdrón-López M, Díaz-Varela M, Zanghi G, Aparici-Herraiz I, Steel RWJ, et al., 2022. Mass Spectrometry Identification of Biomarkers in Extracellular Vesicles From Plasmodium vivax Liver Hypnozoite Infections. Mol Cell Proteomics. 21 (10):100406. doi: 10.1016/j.mcpro.2022.100406.
• Aparici Herraiz I, Caires HR, Castillo-Fernández Ó, Sima N, Méndez-Mora L, et al.,  2022. Advancing Key Gaps in the Knowledge of Plasmodium vivax Cryptic Infections Using Humanized Mouse Models and Organs-on-Chips. Front Cell Infect Microbiol. 12:920204. doi: 10.3389/fcimb.2022.920204
• Brito MAM, Baro B, Raiol TC, Ayllon-Hermida A, Safe IP, et al., 2022. Morphological and Transcriptional Changes in Human Bone Marrow During Natural Plasmodium vivax Malaria Infections. J Infect Dis. 225(7):1274-1283. doi: 10.1093/infdis/jiaa177.
• Kho S, Qotrunnada L, Leonardo L, Andries B, Wardani PAI, et al., 2021. Evaluation of splenic accumulation and colocalization of immature reticulocytes and Plasmodium vivax in asymptomatic malaria: A prospective human splenectomy study. PLoS Med. 18(5):e1003632. doi: 10.1371/journal.pmed.1003632.
• Toda H, Diaz-Varela M, Segui-Barber J, Roobsoong W, Baro B, et al., 2020. Plasma-derived extracellular vesicles from Plasmodium vivax patients signal spleen fibroblasts via NF-kB facilitating parasite cytoadherence. Nat Commun. 11(1):2761. doi:10.1038/s41467-020-16337-y
• Fernandez-Becerra C, Bernabeu M, Castellanos A, Correa BR, Obadia T, et al., 2020. Plasmodium vivax spleen-dependent genes encode antigens associated with cytoadhesion and clinical protection. Proc Natl Acad Sci U S A. 2020;117(23):13056-13065. doi:10.1073/pnas.1920596117

See the full list of publications

NTA ZetaView® Service

Thanks to the support of ISGlobal and the Institute for Health Science Research Germans Trias i Pujol (IGTP), the Plasmodium vivax and Exosomes Research Group, led by Carmen Fernández Becerra and Hernando A. del Portillo, PvREX, has acquired a new Particle Metrix (ZetaView®) equipment for their studies on Extracellular Vesicles (EVs).

Nanoparticle Tracking Analysis (NTA) is a technique used to characterize nanoparticles (EVs, liposomes, VLPs) in suspension ranging between 10 and 2000 nm. This equipment, compared to more conventional ones, allows real-time visualization of particles in suspension, thus calculating their size, dispersion, and fluorescence simultaneously. One of the new improvements we have with the ZetaView® is the addition of the Zeta Potential, which enables the characterization of the surface charge of nanoparticles.

The PvREX group, located at the IGTP, in Badalona, offers the use of this equipment as a laboratory-based service to all groups working on EVs and nanoparticles. This service will have a specialized technician responsible for performing the requested services.

Through the website ZetaView-ISGlobal, all relevant service requests can be made and all available prices can be consulted.