The interaction between Plasmodium vivax Duffy binding protein (PvDBP) and Duffy antigen receptor for chemokines (DARC) has been described as critical for the invasion of human reticulocytes, although increasing reports of P. vivax infections in Duffy-negative individuals questions its unique role. To investigate the genetic diversity of the two main protein ligands for reticulocyte invasion, PvDBP and P. vivax Erythrocyte Binding Protein (PvEBP), we analyzed 458 isolates collected in Cambodia and Madagascar from individuals genotyped as Duffy-positive. First, we observed a high proportion of isolates with multiple copies PvEBP from Madagascar (56%) where Duffy negative and positive individuals coexist compared to Cambodia (19%) where Duffy-negative population is virtually absent. Whether the gene amplification observed is responsible for alternate invasion pathways remains to be tested. Second, we found that the PvEBP gene was less diverse than PvDBP gene (12 vs. 33 alleles) but provided evidence for an excess of nonsynonymous mutations with the complete absence of synonymous mutations. This finding reveals that PvEBP is under strong diversifying selection, and confirms the importance of this protein ligand in the invasion process of the human reticulocytes and as a target of acquired immunity. These observations highlight how genomic changes in parasite ligands improve the fitness of P. vivax isolates in the face of immune pressure and receptor polymorphisms.

CC) ¶ these authors contributed equally to this work provide unique insights into the roles of these two key ligands by studying the genetic diversity of P. vivax isolates collected from Cambodia, where all individuals are Duffy positive, and Madagascar where both Duffy-positive and Duffy-negative individuals coexists. Our data suggest that PvEBP may play an important functional role in invasion into Duffy-negative reticulocytes. PvEBP appears to be a target of naturally acquired antibody responses following natural exposure to P.vivax infection and such as a consequence an important vaccine candidate, together with PvDBP.

Background In low-malaria-transmission areas of Madagascar, annual parasite incidence (API) from routine data has been used to target indoor residual spraying at sub-district commune levels. To assess validity of this approach, we conducted school-based serological surveys and health facility (HF) data quality assessments in seven districts to compare API to “gold-standard” commune-level serological measures. Methods At two primary schools in each of 93 communes, 60 students were randomly selected along with parents and teachers. Capillary blood was drawn for rapid diagnostic tests (RDTs) and serology. Multiplex bead-based immunoassays to detect antibodies to five Plasmodium falciparum antigens were conducted, and finite mixture models used to characterize seronegative and seropositive populations. Reversible catalytic models generated commune-level annual seroconversion rates (SCRs). HF register data were abstracted to assess completeness and accuracy. Results RDT positivity from 12,770 samples was 0.5%. Seroprevalence to tested antigens ranged from 17.9% (MSP-1) to 59.7% (PF13). Median commune-level SCR was 0.0108 (range: 0.001, 0.075). Compared to SCRs, API identified 71% (95% CI: 51%, 87%) of the 30% highest-transmission communes; sensitivity declined at lower levels. Routine data accuracy did not substantially affect API performance. Conclusions API performs reasonably well at identifying higher-transmission communes, but sensitivity declined at lower transmission levels.

Background There is a need for rapid non-sputum-based tests to identify and treat patients infected with Mycobacterium tuberculosis (Mtb). In this study, performance of a human plasma protein signature for both TB triage and treatment monitoring has been evaluated. Methods A panel of seven host proteins CLEC3B, SELL, IGFBP3, IP10, CD14, ECM1 and C1Q were measured in the plasma of a prospective patient cohort undergoing anti-tubercular therapy to distinguish confirmed TB patients from control, to define culture slow and fast converters during an antituberculosis treatment and to monitor the treatment. To validate the protein signatures a Luminex xMAP® assay was used to quantify the proteins in unstimulated plasma isolated from the blood collected from HIV-negative pulmonary TB patients (ATB), at baseline and following 6-months of antituberculosis treatment, latently TB-infected individuals (LTBI) and healthy donors (HD). Protein signatures performances were evaluated using CombiROC algorithm and multivariate models. Findings: We measured the proteins in the plasma of 84 participants including 37 ATB, 24 LTBI and 23 HD. The seven plasma host proteins studied showed different levels between the TB clinical groups and when used separately or in combination, have variable performances for ATB triage and for treatment monitoring. Six of the plasma proteins (CLEC3B, SELL, IGFBP3, IP10, CD14 and C1Q) showed significant differences in normalised median fluorescence intensities when comparing ATB vs HD or LTBI while ECM1 revealed a significant association with early sputum culture conversion after 2 months following treatment (OR 0.004, p = 0.018). For both triage and treatment monitoring, a signature combining 4 host proteins markers (CLEC3B-ECM1-IP10-SELL) was identified, allowing to distinguish ATB from HD or LTBI (respectively, sensitivity = 94%, specificity = 92% and sensitivity = 89%, specificity = 91%) as well as the baseline distinction between slow vs fast sputum culture converters after two months of treatment (AUC = 0.87, sensitivity = 83%, specificity = 84%). Conclusion Our data demonstrate that using a combination of host plasma markers can generate a relevant biosignature for both TB triage and treatment monitoring meeting the WHO Target Product Profile for both purposes.

Background Targeted research on residual malaria transmission is important to improve strategies in settings pursuing elimination, where transmission reductions prove challenging. This study aimed to detect and characterize spatial heterogeneity and factors associated with Plasmodium falciparum infections and exposure, P. falciparum apical membrane antigen 1 (PfAMA1) antibody (Ab) response, in the Central Highlands of Madagascar (CHL). Methods From May to July 2014, a cross-sectional school-based survey was carried out in 182 fokontany (villages) within 7 health districts of the CHL. Rapid diagnostic tests (RDTs) and a bead-based immunoassay including PfAMA1 antigen biomarker were used to estimate malaria prevalence and seroprevalence, respectively. Local Moran’s I index was used to detect spatial “hotspots”. Remotely sensed environmental data—temperature, vegetation indices, land covers, and elevation—were used in multivariable mixed-effects logistic regression models to characterize factors associated with malaria infection and cumulative exposure. Results Among 6,293 school-children ages 2–14 years surveyed, RDT prevalence was low at 0.8% (95% CI 0.6–1.1%), while PfAMA1 Ab seroprevalence was 7.0% (95% CI 6.4–7.7%). Hotspots of PfAMA1 Ab seroprevalence were observed in two districts (Ankazobe and Mandoto). Seroprevalence increased for children living > 5 km from a health centre (adjusted odds ratio (OR) = 1.6, 95% CI 1.2–2.2), and for those experiencing a fever episode in the previous 2 weeks (OR 1.7, 95% CI 1.2–2.4), but decreased at higher elevation (for each 100-m increase, OR = 0.7, 95% CI 0.6–0.8). A clear age pattern was observed whereby children 9–10 years old had an OR of 1.8 (95% CI 1.2–2.4), children 11–12 years an OR of 3.7 (95% CI 2.8–5.0), and children 13–14 years an OR of 5.7 (95% CI 4.0–8.0) for seropositivity, compared with younger children (2–8 years). Conclusion The use of serology in this study provided a better understanding of malaria hotspots and associated factors, revealing a pattern of higher transmission linked to geographical barriers in health care access. The integration of antibody-assays into existing surveillance activities could improve exposure assessment, and may help to monitor the effectiveness of malaria control efforts and adapt elimination interventions.