Patterns of selection onPlasmodium falciparumerythrocyte-binding antigens after the colonization of the New World

Genetic polymorphism and natural selection of the erythrocyte binding antigen 175 region II in Plasmodium falciparum populations from Myanmar and Vietnam

Plasmodium falciparum erythrocyte binding antigen 175 (PfEBA-175) plays essential role in erythrocyte invasion by the parasite and is a leading vaccine candidate. However, its genetic diversity in global isolates is a concern in developing an universal vaccine incorporating this protein. This study aimed to investigate genetic polymorphisms and natural selection of pfeba-175 region II (RII) in Myanmar and Vietnam P. falciparum isolates. Vietnam pfeba-175 RII displayed a low genetic polymorphism, while Myanmar pfeba-175 RII showed high levels of genetic diversity across the region. Point mutations, deletion, and recombinations were main factors contributing to genetic diversities in P. falciparum populations. Global pfeba-175 RII revealed similar, but not identical, genetic polymorphisms and natural selection profiles. Despite profiles of amino acid substitutions differed among populations, five major amino acid changes (K279E, E403K, K481I, Q584K, and R664) were commonly detected in global pfeba-175 RII populations. Haplotype network and genetic differentiation analyses of global pfeba-175 RII populations demonstrated no geographical relationships. Non-neglectable level of genetic diversity was observed in global pfeba-175 RII populations, emphasizing the need to consider this when designing an effective vaccine based on this protein. This study underscores the importance of the continuous monitoring of genetic diversity of pfeba-175 RII in the global P. falciparum populations.

The Effects of HIV Infection on the Immune Response to Malaria Among Pregnant Women in Kumba, Southwest Cameroon: Protocol for a Cross-sectional Study

BACKGROUND

Malaria and HIV, 2 of the world's deadliest diseases, share a lot of territory in sub-Saharan Africa.

OBJECTIVE

This study seeks to investigate the effect of HIV on the immune response to malaria infection among pregnant women in Kumba in the southwest region (SWR) of Cameroon. The study aims to determine the prevalence of malaria infection, assess the occurrence of Plasmodium falciparum genetic diversity, and evaluate the antibody (immunoglobulin [Ig]G and IgM: apical membrane antigen-1 [AMA1], merozoite surface protein [MSP]1, MSP2, MSP3, and erythrocyte-binding antigen [EBA]175) and cytokine (interleukin [IL]-10, tumor necrosis factor alpha [TNF-α], and interferon gamma [IFNγ]) response to malaria infection among pregnant women with and without HIV in Kumba.

METHODS

The study will be a hospital-based cross-sectional design that will run from March 2022 to February 2023. It will recruit pregnant women with and without HIV who are in their third trimester of pregnancy. The study will be carried out in 5 health institutions in Kumba: General Hospital Kumba, Presbyterian Hospital Kumba, District Hospital Kumba-town, Kossala Integrated Health Center Kumba, and Catholic Hospital Kumba. About 3 mL of the mother's venous blood, placental blood, and baby cord blood will be collected from each pregnant women at the point of delivery. Microscopy, rapid diagnostic tests (RDTs), and nested polymerase chain reaction (PCR) will be performed to identify the malaria parasite in all the samples, and nested PCR targeting the different genetic diversity markers for P. falciparum will also be performed. Furthermore, sequencing will be performed to study the nucleotide sequence of different alleles, and the genetic diversity of the alleles responsible for malaria infection among pregnant women will be assessed. A multiplex assay will be conducted to analyze the peripheral blood plasma and cord blood plasma for the cytokine and total antibody response to malaria infection among pregnant women with and without HIV. The questionnaire for data collection will be pretested at the Kumba District Hospital, and ethical clearance will be obtained from the University of Buea and the Regional Delegation of Public Health for the SWR. Data will be analyzed using SPSS Statistics and STATA. All P values <.05 will be considered statistically significant. BioEdit 7.0.0 software will be used to align the nucleotide sequences of different genes after sequencing. Phylogenetic tree searching will be conducted using the maximum-likelihood (ML) method in MEGA V6.0.

RESULTS

The project started in March 2022 and will end in February 2023. Presently, three-fourth of the project funding has been disbursed to date. A total of 218 participants have been enrolled: 193 (88.5%) women without HIV and 25 (11.5%) women with HIV. Between February 2023 and March 2024, the following results will be ready for publication: maternal-neonatal malaria prevalence among pregnant women and babies in Kumba, the effect of HIV on (1) P. falciparum genetic diversity among pregnant women in Kumba, (2) the maternal and neonatal immune response to MSP1, MSP2, and EBA175 IgG antibody response to P. falciparum-caused malaria infection among pregnant women, and (3) the maternal and neonatal pro-inflammatory and anti-inflammatory cytokine response to malaria infection.

CONCLUSIONS

HIV infection increases the prevalence of malaria infection among pregnant women and also influences the genetic diversity of P. falciparum, with MSP1 alleles being the most prevalent. HIV infection also reduces the antibody response to malaria infection, as well as altering the level of pro-inflammatory and anti-inflammatory responses to malaria infection.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/38213.

A population genetic perspective on the origin, spread and adaptation of the human malaria agents Plasmodium falciparum and Plasmodium vivax

Malaria is considered one of the most important scourges that humanity has faced during its history, being responsible every year for numerous deaths worldwide. The disease is caused by protozoan parasites, among which two species are responsible of the majority of the burden, Plasmodium falciparum and Plasmodium vivax. For these two parasite species, the questions of their origin (how and when they appeared in humans), of their spread throughout the world, as well as how they have adapted to humans have long been of interest to the scientific community. Here, we review the current knowledge that has accumulated on these different questions, thanks in particular to the analysis of the genetic and genomic variability of these parasites and comparison with related Plasmodium species infecting other host species (like non-human primates). In this paper we review the existing body of knowledge, including current research dealing with these questions, focusing particularly on genetic analysis and genomic variability of these parasites and comparison with related Plasmodium species infecting other species of host (such as non-human primates).

Genetic structure of two erythrocyte binding antigens of Plasmodium falciparum reveals a contrasting pattern of selection

Erythrocyte binding antigens 175 (EBA-175) and 140 (EBA-140) play key roles in erythrocyte invasion by binding to glycophorin A (GPA) and C (GPC) respectively in human malaria. Since antigenic variation in malaria endemic region is a major barrier to development of effective vaccine, we explore the nature and pattern of sequence diversity of these two vaccine candidates in Kolkata, India. Population genetic parameters based on parasite sequences representing region II of Pfeba-175 and Pfeba-140 genes were estimated using DnaSP V.5.10 and MEGA version 6.0. A novel molecular docking approach was implemented to assess the binding affinities of Kolkata Pfeba-175 variants with GPA. P. falciparum Kolkata isolates experienced a recent population expansion as documented by negative Tajima's D, Fu & Li's statistics, unimodal mismatch distribution and star-like median-joining network for both loci. Positive selection seemed to play a major role in shaping the diversity of Pfeba-175 (d_N/d_S=2.45, and McDonald-Kreitman P-value=0.04) with successive accumulation of Q584K/E, E592A and R664S deriving high frequency haplotypes designated here as F2KH3 and F2KH1. In silico molecular docking demonstrated that polypeptides encoded by F2KH1 and F2KH3 were capable of engaging the parasite ligand into energetically favorable interaction with GPA. Our data demonstrated emergence of Pfeba-175 sequences harboring selectively advantageous nonsynonymous substitutions on Pf3D7 sequence background in the Kolkata parasite isolates. A contrasting pattern of Pf3D7-centric expansion of parasite sequences was noted for Pfeba-140. Together, this study provides a firm genetic and biological support favoring a dominant role of EBA-175 in erythrocyte invasion.

Antigenic Variation in Plasmodium falciparum

Plasmodium falciparum is the protozoan parasite that causes most malaria-associated morbidity and mortality in humans with over 500,000 deaths annually. The disease symptoms are associated with repeated cycles of invasion and asexual multiplication inside red blood cells of the parasite. Partial, non-sterile immunity to P. falciparum malaria develops only after repeated infections and continuous exposure. The successful evasion of the human immune system relies on the large repertoire of antigenically diverse parasite proteins displayed on the red blood cell surface and on the merozoite membrane where they are exposed to the human immune system. Expression switching of these polymorphic proteins between asexual parasite generations provides an efficient mechanism to adapt to the changing environment in the host and to maintain chronic infection. This chapter discusses antigenic diversity and variation in the malaria parasite and our current understanding of the molecular mechanisms that direct the expression of these proteins.