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Mehra S, Taylor PG, McCaw JM, Flegg JA. A hybrid transmission model for Plasmodium vivax accounting for superinfection, immunity and the hypnozoite reservoir. J Math Biol 2024; 89:7. [PMID: 38772937 PMCID: PMC11108905 DOI: 10.1007/s00285-024-02088-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 10/12/2023] [Accepted: 03/25/2024] [Indexed: 05/23/2024]
Abstract
Malaria is a vector-borne disease that exacts a grave toll in the Global South. The epidemiology of Plasmodium vivax, the most geographically expansive agent of human malaria, is characterised by the accrual of a reservoir of dormant parasites known as hypnozoites. Relapses, arising from hypnozoite activation events, comprise the majority of the blood-stage infection burden, with implications for the acquisition of immunity and the distribution of superinfection. Here, we construct a novel model for the transmission of P. vivax that concurrently accounts for the accrual of the hypnozoite reservoir, (blood-stage) superinfection and the acquisition of immunity. We begin by using an infinite-server queueing network model to characterise the within-host dynamics as a function of mosquito-to-human transmission intensity, extending our previous model to capture a discretised immunity level. To model transmission-blocking and antidisease immunity, we allow for geometric decay in the respective probabilities of successful human-to-mosquito transmission and symptomatic blood-stage infection as a function of this immunity level. Under a hybrid approximation-whereby probabilistic within-host distributions are cast as expected population-level proportions-we couple host and vector dynamics to recover a deterministic compartmental model in line with Ross-Macdonald theory. We then perform a steady-state analysis for this compartmental model, informed by the (analytic) distributions derived at the within-host level. To characterise transient dynamics, we derive a reduced system of integrodifferential equations, likewise informed by our within-host queueing network, allowing us to recover population-level distributions for various quantities of epidemiological interest. In capturing the interplay between hypnozoite accrual, superinfection and acquired immunity-and providing, to the best of our knowledge, the most complete population-level distributions for a range of epidemiological values-our model provides insights into important, but poorly understood, epidemiological features of P. vivax.
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Affiliation(s)
- Somya Mehra
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.
| | - Peter G Taylor
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - James M McCaw
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia
- Peter Doherty Institute for Infection and Immunity, The Royal Melbourne Hospital and The University of Melbourne, Parkville, Australia
| | - Jennifer A Flegg
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
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Anwar MN, Smith L, Devine A, Mehra S, Walker CR, Ivory E, Conway E, Mueller I, McCaw JM, Flegg JA, Hickson RI. Mathematical models of Plasmodium vivax transmission: A scoping review. PLoS Comput Biol 2024; 20:e1011931. [PMID: 38483975 DOI: 10.1371/journal.pcbi.1011931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 03/26/2024] [Accepted: 02/19/2024] [Indexed: 03/27/2024] Open
Abstract
Plasmodium vivax is one of the most geographically widespread malaria parasites in the world, primarily found across South-East Asia, Latin America, and parts of Africa. One of the significant characteristics of the P. vivax parasite is its ability to remain dormant in the human liver as hypnozoites and subsequently reactivate after the initial infection (i.e. relapse infections). Mathematical modelling approaches have been widely applied to understand P. vivax dynamics and predict the impact of intervention outcomes. Models that capture P. vivax dynamics differ from those that capture P. falciparum dynamics, as they must account for relapses caused by the activation of hypnozoites. In this article, we provide a scoping review of mathematical models that capture P. vivax transmission dynamics published between January 1988 and May 2023. The primary objective of this work is to provide a comprehensive summary of the mathematical models and techniques used to model P. vivax dynamics. In doing so, we aim to assist researchers working on mathematical epidemiology, disease transmission, and other aspects of P. vivax malaria by highlighting best practices in currently published models and highlighting where further model development is required. We categorise P. vivax models according to whether a deterministic or agent-based approach was used. We provide an overview of the different strategies used to incorporate the parasite's biology, use of multiple scales (within-host and population-level), superinfection, immunity, and treatment interventions. In most of the published literature, the rationale for different modelling approaches was driven by the research question at hand. Some models focus on the parasites' complicated biology, while others incorporate simplified assumptions to avoid model complexity. Overall, the existing literature on mathematical models for P. vivax encompasses various aspects of the parasite's dynamics. We recommend that future research should focus on refining how key aspects of P. vivax dynamics are modelled, including spatial heterogeneity in exposure risk and heterogeneity in susceptibility to infection, the accumulation of hypnozoite variation, the interaction between P. falciparum and P. vivax, acquisition of immunity, and recovery under superinfection.
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Affiliation(s)
- Md Nurul Anwar
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Department of Mathematics, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj, Bangladesh
| | - Lauren Smith
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
| | - Angela Devine
- Division of Global and Tropical Health, Menzies School of Health Research, Charles Darwin University, Darwin, Australia
- Health Economics Unit, Centre for Health Policy, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia
| | - Somya Mehra
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - Camelia R Walker
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - Elizabeth Ivory
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - Eamon Conway
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
| | - Ivo Mueller
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
| | - James M McCaw
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia
| | - Jennifer A Flegg
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - Roslyn I Hickson
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, Australia
- Commonwealth Scientific and Industrial Research Organisation, Townsville, Australia
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Champagne C, Gerhards M, Lana JT, Le Menach A, Pothin E. Quantifying the impact of interventions against Plasmodium vivax: A model for country-specific use. Epidemics 2024; 46:100747. [PMID: 38330786 PMCID: PMC10944169 DOI: 10.1016/j.epidem.2024.100747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 11/03/2023] [Accepted: 01/23/2024] [Indexed: 02/10/2024] Open
Abstract
In order to evaluate the impact of various intervention strategies on Plasmodium vivax dynamics in low endemicity settings without significant seasonal pattern, we introduce a simple mathematical model that can be easily adapted to reported case numbers similar to that collected by surveillance systems in various countries. The model includes case management, vector control, mass drug administration and reactive case detection interventions and is implemented in both deterministic and stochastic frameworks. It is available as an R package to enable users to calibrate and simulate it with their own data. Although we only illustrate its use on fictitious data, by simulating and comparing the impact of various intervention combinations on malaria risk and burden, this model could be a useful tool for strategic planning, implementation and resource mobilization.
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Affiliation(s)
- C Champagne
- Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
| | - M Gerhards
- Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland
| | - J T Lana
- Clinton Health Access Initiative, Boston, USA
| | - A Le Menach
- Clinton Health Access Initiative, Boston, USA
| | - E Pothin
- Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland; Clinton Health Access Initiative, Boston, USA
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Mehra S, McCaw JM, Taylor PG. Superinfection and the hypnozoite reservoir for Plasmodium vivax: a general framework. J Math Biol 2023; 88:7. [PMID: 38040981 PMCID: PMC10692056 DOI: 10.1007/s00285-023-02014-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 10/03/2023] [Accepted: 10/11/2023] [Indexed: 12/03/2023]
Abstract
A characteristic of malaria in all its forms is the potential for superinfection (that is, multiple concurrent blood-stage infections). An additional characteristic of Plasmodium vivax malaria is a reservoir of latent parasites (hypnozoites) within the host liver, which activate to cause (blood-stage) relapses. Here, we present a model of hypnozoite accrual and superinfection for P. vivax. To couple host and vector dynamics for a homogeneously-mixing population, we construct a density-dependent Markov population process with countably many types, for which disease extinction is shown to occur almost surely. We also establish a functional law of large numbers, taking the form of an infinite-dimensional system of ordinary differential equations that can also be recovered by coupling expected host and vector dynamics (i.e. a hybrid approximation) or through a standard compartment modelling approach. Recognising that the subset of these equations that model the infection status of the human hosts has precisely the same form as the Kolmogorov forward equations for a Markovian network of infinite server queues with an inhomogeneous batch arrival process, we use physical insight into the evolution of the latter process to write down a time-dependent multivariate generating function for the solution. We use this characterisation to collapse the infinite-compartment model into a single integrodifferential equation (IDE) governing the intensity of mosquito-to-human transmission. Through a steady state analysis, we recover a threshold phenomenon for this IDE in terms of a parameter [Formula: see text] expressible in terms of the primitives of the model, with the disease-free equilibrium shown to be uniformly asymptotically stable if [Formula: see text] and an endemic equilibrium solution emerging if [Formula: see text]. Our work provides a theoretical basis to explore the epidemiology of P. vivax, and introduces a strategy for constructing tractable population-level models of malarial superinfection that can be generalised to allow for greater biological realism in a number of directions.
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Affiliation(s)
- Somya Mehra
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.
| | - James M McCaw
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia
| | - Peter G Taylor
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
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Nguyen TS, Park JH, Nguyen TK, Nguyen TV, Lee SK, Na SH, Han JH, Park WS, Chun W, Lu F, Han ET. Plasmodium vivax merozoite-specific thrombospondin-related anonymous protein (PvMTRAP) interacts with human CD36, suggesting a novel ligand-receptor interaction for reticulocyte invasion. Parasit Vectors 2023; 16:426. [PMID: 37981686 PMCID: PMC10658926 DOI: 10.1186/s13071-023-06031-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Accepted: 10/24/2023] [Indexed: 11/21/2023] Open
Abstract
BACKGROUND The Plasmodium vivax merozoite restrictively invades immature erythrocytes, suggesting that its ligand(s) might interact with corresponding receptor(s) that are selectively abundant on reticulocytes to complete the invasion. Finding the ligand‒receptor interaction involved in P. vivax invasion is critical to vivax malaria management; nevertheless, it remains to be unraveled. METHODS A library of reticulocyte receptors and P. vivax ligands were expressed by a HEK293E mammalian cell expression system and were then used to screen the interaction using enzyme-linked immunosorbent assay (ELISA). A flow cytometry-based erythrocyte binding assay and bio-layer interferometry experiment were further utilized to cellularly and quantitatively identify the ligand‒receptor interaction, respectively. RESULTS Plasmodium vivax merozoite-specific thrombospondin-related anonymous protein (PvMTRAP) was found to interact with human CD36 using systematic screening. This interaction was specific at a molecular level from in vitro analysis and comparable to that of P. vivax Duffy binding protein (PvDBP) and Duffy antigen receptor for chemokines (DARC) (KD: 37.0 ± 1.4 nM and 7.7 ± 0.5 nM, respectively). Flow cytometry indicated that PvMTRAP preferentially binds to reticulocytes, on which CD36 is selectively present. CONCLUSIONS Human CD36 is selectively abundant on reticulocytes and is able to interact specifically with PvMTRAP, suggesting that it may function as a ligand and receptor during the invasion of reticulocytes by P. vivax.
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Affiliation(s)
- Thau Sy Nguyen
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Ji-Hoon Park
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
- Host-Parasite Research Laboratory, Institut Pasteur Korea, Seongnam-Si, 13488, Republic of Korea
| | - Tuyet-Kha Nguyen
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Truong Van Nguyen
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Seong-Kyun Lee
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Sung-Hun Na
- Department of Obstetrics and Gynecology, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Jin-Hee Han
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Won-Sun Park
- Department of Physiology, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Wanjoo Chun
- Department of Pharmacology, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea
| | - Feng Lu
- Department of Pathogen Biology and Immunology, School of Medicine, Yangzhou University, Yangzhou, China
| | - Eun-Taek Han
- Department of Medical Environmental Biology and Tropical Medicine, School of Medicine, Kangwon National University, Chuncheon, Gangwon-Do, 24341, Republic of Korea.
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Anwar MN, Hickson RI, Mehra S, Price DJ, McCaw JM, Flegg MB, Flegg JA. Optimal Interruption of P. vivax Malaria Transmission Using Mass Drug Administration. Bull Math Biol 2023; 85:43. [PMID: 37076740 PMCID: PMC10115738 DOI: 10.1007/s11538-023-01153-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 03/30/2023] [Indexed: 04/21/2023]
Abstract
Plasmodium vivax is the most geographically widespread malaria-causing parasite resulting in significant associated global morbidity and mortality. One of the factors driving this widespread phenomenon is the ability of the parasites to remain dormant in the liver. Known as 'hypnozoites', they reside in the liver following an initial exposure, before activating later to cause further infections, referred to as 'relapses'. As around 79-96% of infections are attributed to relapses from activating hypnozoites, we expect it will be highly impactful to apply treatment to target the hypnozoite reservoir (i.e. the collection of dormant parasites) to eliminate P. vivax. Treatment with radical cure, for example tafenoquine or primaquine, to target the hypnozoite reservoir is a potential tool to control and/or eliminate P. vivax. We have developed a deterministic multiscale mathematical model as a system of integro-differential equations that captures the complex dynamics of P. vivax hypnozoites and the effect of hypnozoite relapse on disease transmission. Here, we use our multiscale model to study the anticipated effect of radical cure treatment administered via a mass drug administration (MDA) program. We implement multiple rounds of MDA with a fixed interval between rounds, starting from different steady-state disease prevalences. We then construct an optimisation model with three different objective functions motivated on a public health basis to obtain the optimal MDA interval. We also incorporate mosquito seasonality in our model to study its effect on the optimal treatment regime. We find that the effect of MDA interventions is temporary and depends on the pre-intervention disease prevalence (and choice of model parameters) as well as the number of MDA rounds under consideration. The optimal interval between MDA rounds also depends on the objective (combinations of expected intervention outcomes). We find radical cure alone may not be enough to lead to P. vivax elimination under our mathematical model (and choice of model parameters) since the prevalence of infection eventually returns to pre-MDA levels.
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Affiliation(s)
- Md Nurul Anwar
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Department of Mathematics, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj, 8100, Bangladesh
| | - Roslyn I Hickson
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Australian Institute of Tropical Health and Medicine, and College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Australia
- CSIRO, Townsville, Australia
| | - Somya Mehra
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - David J Price
- Department of Infectious Diseases, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, Australia
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia
| | - James M McCaw
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia
| | - Mark B Flegg
- School of Mathematics, Monash University, Melbourne, Australia
| | - Jennifer A Flegg
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.
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Anwar MN, Hickson RI, Mehra S, McCaw JM, Flegg JA. A Multiscale Mathematical Model of Plasmodium Vivax Transmission. Bull Math Biol 2022; 84:81. [PMID: 35778540 PMCID: PMC9249727 DOI: 10.1007/s11538-022-01036-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2021] [Accepted: 05/26/2022] [Indexed: 11/29/2022]
Abstract
Malaria is caused by Plasmodium parasites which are transmitted to humans by the bite of an infected Anopheles mosquito. Plasmodium vivax is distinct from other malaria species in its ability to remain dormant in the liver (as hypnozoites) and activate later to cause further infections (referred to as relapses). Mathematical models to describe the transmission dynamics of P. vivax have been developed, but most of them fail to capture realistic dynamics of hypnozoites. Models that do capture the complexity tend to involve many governing equations, making them difficult to extend to incorporate other important factors for P. vivax, such as treatment status, age and pregnancy. In this paper, we have developed a multiscale model (a system of integro-differential equations) that involves a minimal set of equations at the population scale, with an embedded within-host model that can capture the dynamics of the hypnozoite reservoir. In this way, we can gain key insights into dynamics of P. vivax transmission with a minimum number of equations at the population scale, making this framework readily scalable to incorporate more complexity. We performed a sensitivity analysis of our multiscale model over key parameters and found that prevalence of P. vivax blood-stage infection increases with both bite rate and number of mosquitoes but decreases with hypnozoite death rate. Since our mathematical model captures the complex dynamics of P. vivax and the hypnozoite reservoir, it has the potential to become a key tool to inform elimination strategies for P. vivax.
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Affiliation(s)
- Md Nurul Anwar
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.,Department of Mathematics, Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj, 8100, Bangladesh
| | - Roslyn I Hickson
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.,Australian Institute of Tropical Health and Medicine, and College of Public Health, Medical & Veterinary Sciences, James Cook University, Townsville, Australia.,Health and Biosecurity, CSIRO, Townsville, Australia
| | - Somya Mehra
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia
| | - James M McCaw
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.,Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Parkville, Australia.,Peter Doherty Institute for Infection and Immunity, The Royal Melbourne Hospital and The University of Melbourne, Parkville, Australia
| | - Jennifer A Flegg
- School of Mathematics and Statistics, The University of Melbourne, Parkville, Australia.
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Chahine Z, Le Roch KG. Decrypting the complexity of the human malaria parasite biology through systems biology approaches. FRONTIERS IN SYSTEMS BIOLOGY 2022; 2:940321. [PMID: 37200864 PMCID: PMC10191146 DOI: 10.3389/fsysb.2022.940321] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The human malaria parasite, Plasmodium falciparum, is a unicellular protozoan responsible for over half a million deaths annually. With a complex life cycle alternating between human and invertebrate hosts, this apicomplexan is notoriously adept at evading host immune responses and developing resistance to all clinically administered treatments. Advances in omics-based technologies, increased sensitivity of sequencing platforms and enhanced CRISPR based gene editing tools, have given researchers access to more in-depth and untapped information about this enigmatic micro-organism, a feat thought to be infeasible in the past decade. Here we discuss some of the most important scientific achievements made over the past few years with a focus on novel technologies and platforms that set the stage for subsequent discoveries. We also describe some of the systems-based methods applied to uncover gaps of knowledge left through single-omics applications with the hope that we will soon be able to overcome the spread of this life-threatening disease.
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