Plasmodium vivax From Duffy-Negative and Duffy-Positive Individuals Share Similar Gene Pools in East Africa

Origin of the human malaria parasite Plasmodium vivax

The geographic origin of Plasmodium vivax, a leading cause of human malaria, has been the subject of much speculation. Here we review the evolutionary history of P. vivax and P. vivax-like parasites in humans and non-human primates on three continents, providing overwhelming evidence for an African origin. This conclusion is consistent with recent reports showing that Duffy-negative humans in Africa are, in fact, susceptible to P. vivax, with parasites invading Duffy-antigen-expressing erythroid precursors. Thus, the African origin of P. vivax not only explains the distribution of the Duffy-negative genotype but also provides new insight into the history and status of P. vivax malaria in Africa and efforts geared toward its eradication.

Prevalence and Characteristics of Plasmodium vivax Gametocytes in Duffy-Positive and Duffy-Negative Populations across Ethiopia

Plasmodium parasites replicate asexually in human hosts. The proportion of infections that carries gametocytes is a proxy for human-to-mosquito transmissibility. It is unclear which proportion of Plasmodium vivax infections in Duffy-negative populations carries gametocytes. We determined the prevalence and characteristics of P. vivax gametocytes in Duffy-positive and -negative populations across broad regions of Ethiopia. Finger-prick blood samples were collected for microscopic and molecular screening of Plasmodium parasites and Duffy status of individuals. Molecular screening of Plasmodium species and Duffy blood group genotyping was done using SYBR green and the Taqman quantitative polymerase chain reaction method. Of the 447 febrile patients who were shown to be P. vivax smear positive, 414 (92.6%) were confirmed by molecular screening as P. vivax and 16 (3.9%) of them were from Duffy-negative individuals. Of these, 5 of 16 (31.3%) Duffy-negative P. vivax-infected samples were detected with gametocytes. Of the 398 Duffy-positive P. vivax-infected samples, 150 (37.7%) were detected with gametocytes, slightly greater than that in Duffy-negative samples. This study highlights the presence of P. vivax gametocytes in Duffy-negative infections, suggestive of human-to-mosquito transmissibility. Although P. vivax infections in Duffy-negative individuals were commonly associated with low parasitemia, some of these infections were shown to have relatively high parasitemia and may represent a prominent erythrocyte invasion capability of P. vivax, and hidden reservoirs that can contribute to transmission. A better understanding of P. vivax transmission biology and gametocyte function particularly in Duffy-negative populations would aid future treatment and management of P. vivax malaria in Africa.

Comparative transcriptomics reveal differential gene expression among Plasmodium vivax geographical isolates and implications on erythrocyte invasion mechanisms

The documentation of Plasmodium vivax malaria across Africa especially in regions where Duffy negatives are dominant suggests possibly alternative erythrocyte invasion mechanisms. While the transcriptomes of the Southeast Asian and South American P. vivax are well documented, the gene expression profile of P. vivax in Africa is unclear. In this study, we examined the expression of 4,404 gene transcripts belong to 12 functional groups and 43 erythrocyte binding gene candidates in Ethiopian isolates and compared them with the Cambodian and Brazilian P. vivax transcriptomes. Overall, there were 10-26% differences in the gene expression profile amongst geographical isolates, with the Ethiopian and Cambodian P. vivax being most similar. Majority of the gene transcripts involved in protein transportation, housekeeping, and host interaction were highly transcribed in the Ethiopian isolates. Members of the reticulocyte binding protein PvRBP2a and PvRBP3 expressed six-fold higher than Duffy binding protein PvDBP1 and 60-fold higher than PvEBP/DBP2 in the Ethiopian isolates. Other genes including PvMSP3.8, PvMSP3.9, PvTRAG2, PvTRAG14, and PvTRAG22 also showed relatively high expression. Differential expression patterns were observed among geographical isolates, e.g., PvDBP1 and PvEBP/DBP2 were highly expressed in the Cambodian but not the Brazilian and Ethiopian isolates, whereas PvRBP2a and PvRBP2b showed higher expression in the Ethiopian and Cambodian than the Brazilian isolates. Compared to Pvs25, gametocyte genes including PvAP2-G, PvGAP (female gametocytes), and Pvs47 (male gametocytes) were highly expressed across geographical samples.

Prevalence and characteristics of Plasmodium vivax Gametocytes in Duffy-positive and Duffy-negative populations across Ethiopia

Plasmodium parasites replicate asexually in the human host. The proportion of infections that carries gametocytes is a proxy for human-to-mosquito transmissibility. It is unclear what proportion of P. vivax infections in Duffy-negatives carries gametocytes. This study aims to determine the prevalence of P. vivax in Duffy-negatives across broad regions of Ethiopia and characterize parasite stages. Finger-prick blood samples were collected for microscopic and molecular screening of Plasmodium parasites and Duffy status of individuals. Molecular screening of plasmodium species and Duffy blood group genotyping was done using SYBR green and Taqman qPCR method. Among the total 447 samples, 414 (92.6%) were P. vivax confirmed and, 16 (3.9%) of them were from Duffy-negatives. Of these, 5/16 (31.3%) Duffy-negative P. vivax-infected samples were detected with gametocytes. Of the 398 Duffy-positive P. vivax-infected samples, 150 (37.7%) were detected with gametocytes, slightly higher than that in Duffy-negatives. This study highlights the presence of P. vivax gametocytes in Duffy-negative infections, suggestive of human-to-mosquito transmissibility. Although P. vivax infections in Duffy-negatives are commonly associated with low parasitemia, some of these infections were shown with relatively high parasitemia and may represent better erythrocyte invasion capability of P. vivax and hidden reservoirs that can contribute to transmission. A better understanding of P. vivax transmission biology and gametocyte function particularly in Duffy-negative populations would aid future treatment and management of vivax malaria in Africa.

Determination of Plasmodium vivax and Plasmodium falciparum Malaria Exposure in Two Ethiopian Communities and Its Relationship to Duffy Expression

Despite historical dogma that Duffy blood group negativity of human erythrocytes confers resistance to Plasmodium vivax blood stage infection, cases of P. vivax malaria and asymptomatic blood stage infection (subclinical malaria) have recently been well documented in Duffy-negative individuals throughout Africa. However, the impact of Duffy negativity on the development of naturally acquired immunity to P. vivax remains poorly understood. We examined antibody reactivity to P. vivax and P. falciparum antigens at two field sites in Ethiopia and assessed Duffy gene expression by polymerase chain reaction amplification and sequencing of the GATA-1 transcription factor-binding site of the Duffy antigen receptor for chemokines (DARC) gene promotor region that is associated with silencing of erythroid cell transcription and absent protein expression. Antibodies to three of the four P. vivax blood stage antigens examined, RBP2b, EBP2, and DBPIISal-1, were significantly lower (P < 0.001) in Duffy-negative individuals relative to Duffy-positive individuals. In stark contrast, no clear pattern was found across Duffy-negative and Duffy-positive genotypes for P. falciparum antibodies. We conclude that lack of erythroid Duffy expression is associated with reduced serologic responses, indicative of less naturally acquired immunity and less cumulative exposure to blood stage P. vivax parasites relative to Duffy positive individuals living in the same communities.

Relationship between Duffy Genotype/Phenotype and Prevalence of Plasmodium vivax Infection: A Systematic Review

The Duffy protein, a transmembrane molecule, functions as a receptor for various chemokines and facilitates attachment between the reticulocyte and the Plasmodium Duffy antigen-binding protein. Duffy expression correlates with the Duffy receptor gene for the chemokine, located on chromosome 1, and exhibits geographical variability worldwide. Traditionally, researchers have described the Duffy negative genotype as a protective factor against Plasmodium vivax infection. However, recent studies suggest that this microorganism's evolution could potentially diminish this protective effect. Nevertheless, there is currently insufficient global data to demonstrate this phenomenon. This study aimed to evaluate the relationship between the Duffy genotype/phenotype and the prevalence of P. vivax infection. The protocol for the systematic review was registered in PROSPERO as CRD42022353427 and involved reviewing published studies from 2012 to 2022. The Medline/PubMed, Web of Science, Scopus, and SciELO databases were consulted. Assessments of study quality were conducted using the STROBE and GRADE tools. A total of 34 studies were included, with Africa accounting for the majority of recorded studies. The results varied significantly regarding the relationship between the Duffy genotype/phenotype and P. vivax invasion. Some studies predominantly featured the negative Duffy genotype yet reported no malaria cases. Other studies identified minor percentages of infections. Conversely, certain studies observed a higher prevalence (99%) of Duffy-negative individuals infected with P. vivax. In conclusion, this systematic review found that the homozygous Duffy genotype positive for the A allele (FY*A/*A) is associated with a higher incidence of P. vivax infection. Furthermore, the negative Duffy genotype does not confer protection against vivax malaria.

Implementing landscape genetics in molecular epidemiology to determine drivers of vector-borne disease: A malaria case study

This study employs landscape genetics to investigate the environmental drivers of a deadly vector-borne disease, malaria caused by Plasmodium falciparum, in a more spatially comprehensive manner than any previous work. With 1804 samples from 44 sites collected in western Kenya in 2012 and 2013, we performed resistance surface analysis to show that Lake Victoria acts as a barrier to transmission between areas north and south of the Winam Gulf. In addition, Mantel correlograms clearly showed significant correlations between genetic and geographic distance over short distances (less than 70 km). In both cases, we used an identity-by-state measure of relatedness tailored to find highly related individual parasites in order to focus on recent gene flow that is more relevant to disease transmission. To supplement these results, we performed conventional population genetics analyses, including Bayesian clustering methods and spatial ordination techniques. These analyses revealed some differentiation on the basis of geography and elevation and a cluster of genetic similarity in the lowlands north of the Winam Gulf of Lake Victoria. Taken as a whole, these results indicate low overall genetic differentiation in the Lake Victoria region, but with some separation of parasite populations north and south of the Winam Gulf that is explained by the presence of the lake as a geographic barrier to gene flow. We recommend similar landscape genetics analyses in future molecular epidemiology studies of vector-borne diseases to extend and contextualize the results of traditional population genetics.

Comparative transcriptomics reveal differential gene expression in Plasmodium vivax geographical isolates and implications on erythrocyte invasion mechanisms

Plasmodium vivax uses Duffy binding protein (PvDBP1) to bind to the Duffy Antigen-Chemokine Receptor (DARC) to invade human erythrocytes. Individuals who lack DARC expression (Duffy-negative) are thought to be resistance to P. vivax. In recent years, P. vivax malaria is becoming more prevalent in Africa with a portion of these cases detected in Duffy-negatives. Apart from DBP1, members of the reticulocyte binding protein (RBP) and tryptophan-rich antigen (TRAg) families may also play a role in erythrocyte invasion. While the transcriptomes of the Southeast Asian and South American P. vivax are well documented, the gene expression profile of P. vivax in Africa and more specifically the expression level of several erythrocyte binding gene candidates as compared to DBP1 are largely unknown. This paper characterized the first P. vivax transcriptome in Africa and compared with those from the Southeast Asian and South American isolates. The expression of 4,404 gene transcripts belong to 12 functional groups including 43 specific erythrocyte binding gene candidates were examined. Overall, there were 10-26% differences in the gene expression profile amongst the geographical isolates, with the Ethiopian and Cambodian P. vivax being most similar. Majority of the gene transcripts involved in protein transportation, housekeeping, and host interaction were highly transcribed in the Ethiopian P. vivax. Erythrocyte binding genes including PvRBP2a and PvRBP3 expressed six-fold higher than PvDBP1and 60-fold higher than PvEBP/DBP2. Other genes including PvRBP1a, PvMSP3.8, PvMSP3.9, PvTRAG2, PvTRAG14, and PvTRAG22 also showed relatively high expression. Differential expression was observed among geographical isolates, e.g., PvDBP1 and PvEBP/DBP2 were highly expressed in the Cambodian but not the Brazilian and Ethiopian isolates, whereas PvRBP2a and PvRBP2b showed higher expression in the Ethiopian and Cambodian than the Brazilian isolates. Compared to Pvs25, the standard biomarker for detecting female gametocytes, PvAP2-G (PVP01_1440800), GAP (PVP01_1403000), and Pvs47 (PVP01_1208000) were highly expressed across geographical samples. These findings provide an important baseline for future comparisons of P. vivax transcriptomes from Duffy-negative infections and highlight potential biomarkers for improved gametocyte detection.

The Black Box of Cellular and Molecular Events of Plasmodium vivax Merozoite Invasion into Reticulocytes

Plasmodium vivax is the most widely distributed malaria parasite affecting humans worldwide, causing ~5 million cases yearly. Despite the disease's extensive burden, there are gaps in the knowledge of the pathophysiological mechanisms by which P. vivax invades reticulocytes. In contrast, this crucial step is better understood for P. falciparum, the less widely distributed but more often fatal malaria parasite. This discrepancy is due to the difficulty of studying P. vivax's exclusive invasion of reticulocytes, which represent 1-2% of circulating cells. Its accurate targeting mechanism has not yet been clarified, hindering the establishment of long-term continuous in vitro culture systems. So far, only three reticulocyte invasion pathways have been characterised based on parasite interactions with DARC, TfR1 and CD98 host proteins. However, exposing the parasite's alternative invasion mechanisms is currently being considered, opening up a large field for exploring the entry receptors used by P. vivax for invading host cells. New methods must be developed to ensure better understanding of the parasite to control malarial transmission and to eradicate the disease. Here, we review the current state of knowledge on cellular and molecular mechanisms of P. vivax's merozoite invasion to contribute to a better understanding of the parasite's biology, pathogenesis and epidemiology.

Population genomics in neglected malaria parasites

Malaria elimination includes neglected human malaria parasites Plasmodium vivax, Plasmodium ovale spp., and Plasmodium malariae. Biological features such as association with low-density infection and the formation of hypnozoites responsible for relapse make their elimination challenging. Studies on these parasites rely primarily on clinical samples due to the lack of long-term culture techniques. With improved methods to enrich parasite DNA from clinical samples, whole-genome sequencing of the neglected malaria parasites has gained increasing popularity. Population genomics of more than 2200 P. vivax global isolates has improved our knowledge of parasite biology and host-parasite interactions, identified vaccine targets and potential drug resistance markers, and provided a new way to track parasite migration and introduction and monitor the evolutionary response of local populations to elimination efforts. Here, we review advances in population genomics for neglected malaria parasites, discuss how the rich genomic information is being used to understand parasite biology and epidemiology, and explore opportunities for the applications of malaria genomic data in malaria elimination practice.

African Plasmodium vivax malaria improbably rare or benign

The overwhelming dominance of Duffy blood group negativity among most people living in sub-Saharan Africa has been considered the basis of their protection from endemic Plasmodium vivax malaria. New evidence demonstrates widespread transmission of P. vivax in Duffy-negative Africa, though currently of unknown distribution, magnitude, or consequences. Other new evidence from outside of Africa demonstrates marked tropisms of P. vivax for extravascular tissues of bone marrow and spleen. Those establish states of proliferative infection with low-grade or undetectable parasitemia of peripheral blood causing acute and chronic disease. This review examines the plausibility of those infectious processes also operating in Duffy-negative Africans and causing harm of unrecognized origin.

Gene Polymorphisms Among Plasmodium vivax Geographical Isolates and the Potential as New Biomarkers for Gametocyte Detection

The unique biological features of Plasmodium vivax not only make it difficult to control but also to eliminate. For the transmission of the malaria parasite from infected human to the vector, gametocytes play a major role. The transmission potential of a malarial infection is inferred based on microscopic detection of gametocytes and molecular screening of genes in the female gametocytes. Microscopy-based detection methods could grossly underestimate the reservoirs of infection as gametocytes may occur as submicroscopic or as micro- or macro-gametocytes. The identification of genes that are highly expressed and polymorphic in male and female gametocytes is critical for monitoring changes not only in their relative proportions but also the composition of gametocyte clones contributing to transmission over time. Recent transcriptomic study revealed two distinct clusters of highly correlated genes expressed in the P. vivax gametocytes, indicating that the male and female terminal gametocytogeneses are independently regulated. However, the detective power of these genes is unclear. In this study, we compared genetic variations of 15 and 11 genes expressed, respectively, in the female and male gametocytes among P. vivax isolates from Southeast Asia, Africa, and South America. Further, we constructed phylogenetic trees to determine the resolution power and clustering patterns of gametocyte clones. As expected, Pvs25 (PVP01_0616100) and Pvs16 (PVP01_0305600) expressed in the female gametocytes were highly conserved in all geographical isolates. In contrast, genes including 6-cysteine protein Pvs230 (PVP01_0415800) and upregulated in late gametocytes ULG8 (PVP01_1452800) expressed in the female gametocytes, as well as two CPW-WPC family proteins (PVP01_1215900 and PVP01_1320100) expressed in the male gametocytes indicated considerably high nucleotide and haplotype diversity among isolates. Parasite samples expressed in male and female gametocyte genes were observed in separate phylogenetic clusters and likely represented distinct gametocyte clones. Compared to Pvs25, Pvs230 (PVP01_0415800) and a CPW-WPC family protein (PVP01_0904300) showed higher expression in a subset of Ethiopian P. vivax samples. Thus, Pvs230, ULG8, and CPW-WPC family proteins including PVP01_0904300, PVP01_1215900, and PVP01_1320100 could potentially be used as novel biomarkers for detecting both sexes of P. vivax gametocytes in low-density infections and estimating transmission reservoirs.

Prevalence and risk of Plasmodium vivax infection among Duffy-negative individuals: a systematic review and meta-analysis

A better understanding of the occurrence and risk of Plasmodium vivax infection among Duffy-negative individuals is required to guide further research on these infections across Africa. To address this, we used a meta-analysis approach to investigate the prevalence of P. vivax infection among Duffy-negative individuals and assessed the risk of infection in these individuals when compared with Duffy-positive individuals. This study was registered with The International Prospective Register of Systematic Reviews website (ID: CRD42021240202) and followed Preferred Reporting Items for Systematic review and Meta-Analyses guidelines. Literature searches were conducted using medical subject headings to retrieve relevant studies in Medline, Web of Science, and Scopus, from February 22, 2021 to January 31, 2022. Selected studies were methodologically evaluated using the Joanna Briggs Institute (JBI) Critical Appraisal Tools to assess the quality of cross-sectional, case–control, and cohort studies. The pooled prevalence of P. vivax infection among Duffy-negative individuals and the odds ratio (OR) of infection among these individuals when compared with Duffy-positive individuals was estimated using a random-effects model. Results from individual studies were represented in forest plots. Heterogeneity among studies was assessed using Cochrane Q and I² statistics. We also performed subgroup analysis of patient demographics and other relevant variables. Publication bias among studies was assessed using funnel plot asymmetry and the Egger’s test. Of 1593 retrieved articles, 27 met eligibility criteria and were included for analysis. Of these, 24 (88.9%) reported P. vivax infection among Duffy-negative individuals in Africa, including Cameroon, Ethiopia, Sudan, Botswana, Nigeria, Madagascar, Angola, Benin, Kenya, Mali, Mauritania, Democratic Republic of the Congo, and Senegal; while three reported occurrences in South America (Brazil) and Asia (Iran). Among studies, 11 reported that all P. vivax infection cases occurred in Duffy-negative individuals (100%). Also, a meta-analysis on 14 studies showed that the pooled prevalence of P. vivax infection among Duffy-negative individuals was 25% (95% confidence interval (CI) − 3%–53%, I² = 99.96%). A meta-analysis of 11 studies demonstrated a decreased odds of P. vivax infection among Duffy-negative individuals (p = 0.009, pooled OR 0.46, 95% CI 0.26–0.82, I² = 80.8%). We confirmed that P. vivax infected Duffy-negative individuals over a wide prevalence range from 0 to 100% depending on geographical area. Future investigations on P. vivax infection in these individuals must determine if Duffy-negativity remains a protective factor for P. vivax infection.