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Assessing the prevalence of toxoplasmosis in pregnant women and the associated risk factors is the first step in defining policy for the prevention of congenital toxoplasmosis in a given population. An epidemiological study was conducted during prenatal consultations at the CHU-MEL of Cotonou (Benin) between September 2018 and April 2021 and recruited 549 pregnant women to determine the seroprevalence and potential factors associated with Toxoplasma gondii infection. Toxoplasma gondii IgG/IgM antibodies were detected using an enzyme-linked fluorescence assay (ELFA) technique, an IgG avidity test and an IgG/IgM comparative Western blot to diagnose the maternal toxoplasmosis serological status, the possibility of an infection acquired during pregnancy and congenital infection, respectively. Concomitantly, the participants answered a questionnaire investigating potential risk factors. Toxoplasmosis seroprevalence was estimated at 44.4% (95% CI 40.3–48.6) and the factors significantly associated with T. gondii seropositivity were: age over 30 years, multigravid women and contact with cats. The possibility of an infection acquired during the periconceptional period or the first trimester of pregnancy concerned six women [1.1% (95% CI 0.5–2.0)]. However, due to the low rate of serological controls in seronegative women, a significant proportion of women first tested during the 3rd trimester of pregnancy, and an insufficient sample size, the incidence of primary infection during pregnancy could not be determined. No cases of congenital transmission occurred in the newborns from the suspected cases of primary infection.

Abstract Background Pregnancy-associated malaria (PAM) is a serious consequence of Plasmodium falciparum-infected erythrocytes sequestration in the placenta through the adhesion to the placental receptor chondroitin sulfate A (CSA). Although women become resistant to PAM as they acquire transcending inhibitory immunity against CSA-binding parasites, hundreds of thousands of lives could be saved if a prophylactic vaccine targeting the surface proteins of placental parasites could be designed. Recent works point to the variant protein var2CSA as the key target for the development of a pregnancy-associated malaria vaccine. However, designing such a prophylactic vaccine has been hindered by the difficulty in identifying regions of var2CSA that could elicit broadly neutralizing and adhesion-blocking antibodies. Methods Var2CSA is a very large protein with an estimated molecular weight of 350 kDa, and can be divided into six cysteine rich Duffy binding-like domains (DBL). The human embryonic kidney 293 cell line (HEK293) was used to produce secreted soluble recombinant forms of var2CSA DBL domains. The Escherichia coli expression system was also assessed for the domains not expressed or expressed in low amount in the HEK293 system. To investigate whether var2CSA binding DBL domains can induce biologically active antibodies recognizing the native var2CSA and blocking the interaction, mice were immunized with the refolded DBL3-X or the HEK293 secreted DBL6-ε domains. Results Using the HEK293 expression system, DBL1-X, DBL4-ε and DBL6-ε were produced at relatively high levels in the culture supernatant, while DBL3-X and DBL5-ε were produced at much lower levels. DBL2-X and DBL3-X domains were obtained after refolding of the inclusion bodies produced in E. coli. Importantly, mice antisera raised against the recombinant DBL6-ε domain, specifically reacted against the surface of CSA-binding parasites and revealed adhesion blocking activity. Conclusion This is the first report showing inhibitory binding antibodies obtained through a var2CSA recombinant DBL domain immunization protocol. These results support the current strategies using var2CSA as immunogen in the aim of blocking placental sequestration of malaria parasites. This work is a step towards the development of a var2CSA based vaccine that will prevent pregnancy-associated malaria and improve pregnancy outcomes.

Apicomplexa phylum includes numerous obligate intracellular protozoan parasites that are life threatening for humans and animals. In this context, Plasmodium falciparum and Toxoplasma gondii are of particular interest, as they are responsible for malaria and toxoplasmosis, respectively, for which efficient vaccines are presently lacking and therapies need to be improved. Apicomplexan parasites have a highly polarized morphology, with their apical end containing specific secretory organelles named rhoptries and micronemes, which depend on the unique receptor and transporter sortilin TgSORT for their biogenesis. In the present study, we took advantage of the subcellular polarity of the parasite to engineer a clonal transgenic Toxoplasma line that expresses simultaneously the green fluorescent protein TgSORT-GFP in the post-Golgi-endosome-like compartment and the red fluorescent protein rhoptry ROP1-mCherry near the apical end. We utilized this fluorescent transgenic T. gondii to develop a miniaturized image-based phenotype assay coupled to an automated image analysis. By applying this methodology to 1,120 compounds, we identified 12 that are capable of disrupting the T. gondii morphology and inhibiting intracellular replication. Analysis of the selected compounds confirmed that all 12 are kinase inhibitors and intramembrane pumps, with some exhibiting potent activity against Plasmodium falciparum. Our findings highlight the advantage of comparative and targeted phenotypic analysis involving two related parasite species as a means of identifying molecules with a conserved mode of action.

Abstract Background Immunoglobulin G (IgG) antibodies are thought to play important roles in the protection against Plasmodium falciparum (P. falciparum) malaria. A longitudinal cohort study performed in the Southern part of Benin, identified a group of infants who were able to control asymptomatic malaria infections (CAIG). Methods IgG antibodies against distinct merozoite antigens were quantified in plasma from Beninese infants. Functionality of these antibodies was assessed by the merozoite-phagocytosis assay using THP-1 cells and primary neutrophils as effector cells. Gm allotypes were determined by a serological method of haemagglutination inhibition. Results Purified IgG from infants in CAIG promoted higher levels of merozoite-phagocytosis than did IgG from children who were unable to control asymptomatic infections (Ologit multivariate regression model, Coef. = 0.06, 95% CI 0.02;0.10, P = 0.002). High level of merozoite-phagocytosis activity was significantly associated with high levels of IgG against AMA1 (Coef. = 1.76, 95% CI 0.39;3.14, P = 0.012) and GLURP-R2 (Coef. = 12.24, 95% CI 1.35;23.12, P = 0.028). Moreover, infants of the G3m5,6,10,11,13,14,24 phenotype showed higher merozoite-phagocytosis activity (Generalized linear model multivariate regression, Coef. = 7.46, 95% CI 0.31;14.61, P = 0.041) than those presenting other G3m phenotypes. Conclusion The results of the present study confirm the importance of antibodies to merozoite surface antigens in the control of asymptomatic malaria infection in Beninese infants. The study also demonstrated that G3m phenotypes impact the functional activity of IgG. This last point could have a considerable impact in the research of candidate vaccines against malaria parasites or other pathogens.

Introduction: Recently, efforts to eliminate malaria have shifted focus from symptomatic cases alone to include asymptomatic carriers, who are now recognized as significant contributors to the disease's transmission and control. This study examines the relationship between asymptomatic malaria infection and hemoglobin levels in Benin. Methods: A cohort in Benin was enrolled and categorized into three age groups (under 5 years, 5–15 years, and over 15 years) for follow-up from August to November 2021. Participants were monitored over two months and assessed for malaria infection through microscopy and polymerase chain reaction (PCR) during their three visits. A questionnaire was employed to gather general and clinical characteristics. Multivariate models were utilized to analyze the associations between asymptomatic infection, anemia, and hemoglobin levels. Results: Among 393 participants, 58.2% were diagnosed at enrolment with malaria via PCR, and 30.5% through microscopy. Anemia, defined as hemoglobin levels < 11 g/dL, was observed in 40.5% of the cohort. The risk of anemia declined with increasing age (OR for ages 5–15: 0.64, 95% CI [0.37; 1.09]; OR for over 15 years: 0.34, 95% CI [0.20; 0.59]) compared to children under 5. Individuals with both microscopic and submicroscopic infections exhibited higher odds of anemia (respectively OR = 4.15, 95% CI [2.41; 7.13] and OR = 2.09 [1.22; 3.57]) relative to those uninfected. Hemoglobin levels were consistently lower in participants with microscopic malaria across all age groups (β = -2.73, 95% CI [-3.41; -2.05] for those under 5, β = -1.35, 95% CI [-1.89; -0.82] for ages 5–15, and β = -0.72, 95% CI [-1.34; -0.07]) compared to non-infected individuals. Discussion: Our findings suggest that asymptomatic malaria infections, including submicroscopic cases, are associated with anemia and decreased hemoglobin levels. This underscores the importance of employing ultrasensitive diagnostic methods for such infections and acknowledging their potential health implications. [ABSTRACT FROM AUTHOR]

Introduction: Asymptomatic malaria infection is now recognized as a potential threat to malaria control. However, its prevalence and its dynamics are poorly documented especially in a perennial context of high seasonal transmission. A longitudinal study was conducted in southern Benin to investigate the dynamics of asymptomatic malaria infection and to identify factors influencing it. Methods: A cohort of 377 participants was recruited, stratified into three age groups (under 5 years, between 5 and 15 years, over 15 years). After inclusion, two visits were made one-month apart between August and November 2021. Malaria infection was diagnosed by microscopy and PCR and questionnaires were administered to the participants. The dynamics of malaria infection, both submicroscopic (positive PCR / negative blood smear) and microscopic (positive blood smear), and related factors were determined using a mixed ordinal polytomous regression model and a multistate Markov model. Results: The human infectious reservoir consisted primarily of asymptomatic submicroscopic infections (289/512 (56.4%)), followed by asymptomatic microscopic infections (182/512 (35.5%)) and symptomatic infections (41/512 (8%)). The prevalence of asymptomatic infection was highly related to age-group (5–15 years: OR: 4.12 [2.55–6.67] and > 15 years OR: 2.80 [1.73–4.54] compared to the under 5 years old group). The children under 15 years with asymptomatic infection had the highest risk of becoming symptomatic. The mean duration of asymptomatic infections in 5–15-year-olds was the longest (76.7 days (53.8–109.1)). Conclusion: This study revealed a persistent asymptomatic malaria reservoir over the follow-up period, with substantial variations between age-groups. These findings are important elements to consider for an optimal deployment of malaria control interventions. [ABSTRACT FROM AUTHOR]

BackgroundPlacental malaria (PM) is associated with a higher susceptibility of infants to Plasmodium falciparum (Pf) malaria. A hypothesis of immune tolerance has been suggested but no clear explanation has been provided so far. Our goal was to investigate the involvement of inhibitory receptors LILRB1 and LILRB2, known to drive immune evasion upon ligation with pathogen and/or host ligands, in PM-induced immune tolerance.MethodInfants of women with or without PM were enrolled in Allada, southern Benin, and followed-up for 24 months. Antibodies with specificity for five blood stage parasite antigens were quantified by ELISA, and the frequency of immune cell subsets was quantified by flow cytometry. LILRB1 or LILRB2 expression was assessed on cells collected at 18 and 24 months of age.FindingsInfants born to women with PM had a higher risk of developing symptomatic malaria than those born to women without PM (IRR=1.53, p=0.040), and such infants displayed a lower frequency of non-classical monocytes (OR=0.74, p=0.01) that overexpressed LILRB2 (OR=1.36, p=0.002). Moreover, infants born to women with PM had lower levels of cytophilic IgG and higher levels of IL-10 during active infection.InterpretationModulation of IgG and IL-10 levels could impair monocyte functions (opsonisation/phagocytosis) in infants born to women with PM, possibly contributing to their higher susceptibility to malaria. The long-lasting effect of PM on infants’ monocytes was notable, raising questions about the capacity of ligands such as Rifins or HLA-I molecules to bind to LILRB1 and LILRB2 and to modulate immune responses, and about the reprogramming of neonatal monocytes/macrophages.

This article, titled "Editorial: Immune tolerance and human malaria," explores the relationship between immune tolerance and malaria. The authors discuss how exposure to malaria parasites can affect susceptibility to malaria and other pathogens. They also examine the mechanisms underlying immune tolerance to blood-stage infection and the role of immunoregulatory cells in limiting immunopathology. The article highlights the potential impact of malaria-induced immune tolerance on vaccine efficacy and suggests strategies to overcome immune tolerance to improve vaccine effectiveness. The authors present several studies that investigate the modulation of immune responses during malaria infection and its implications for host protection and vaccine development. [Extracted from the article]