Non-falciparum malaria infection and IgG seroprevalence among children under 15 years in Nigeria, 2018

Evaluating Malaria Rapid Diagnostic Tests and Microscopy for Detecting Plasmodium Infection and Status of Plasmodium falciparum Histidine-Rich Protein 2/3 Gene Deletions in Southeastern Nigeria

Delays in malaria diagnosis increase treatment failures and deaths. In endemic regions, standard diagnostic methods are microscopy and malaria rapid diagnostic tests (mRDTs) detecting Plasmodium falciparum histidine-rich protein 2/3 (PFHRP2/PFHRP3), but gene deletions can allow certain parasites to remain undetected. We enlisted a cohort comprising 207 symptomatic individuals, encompassing both children and adults, at a hospital in Nnewi, Nigeria. The prevalence of parasites was determined using a highly sensitive, species-specific quantitative polymerase chain reaction (SS-qPCR). Within a subset of 132 participants, we assessed the sensitivity and specificity of microscopy and HRP2-mRDTs in comparison to SS-qPCR for the detection of P. falciparum. We also investigated the prevalence of pfhrp2/pfhrp3 gene deletions. Greater sensitivity was achieved with mRDTs (95%) compared with microscopy (77%). Also, mRDTs exhibited greater specificity (68%) than microscopy (44%). The positive predictive value of mRDTs (89%) surpassed that of microscopy (80%), suggesting a greater probability of accurately indicating the presence of infection. The negative predictive value of mRDTs (82%) was far greater than microscopy (39%). Of the 165 P. falciparum-positive samples screened for pfhrp2/pfhrp3 gene deletions, one gene deletion was detected in one sample. Regarding infection prevalence, 84% were positive for Plasmodium spp. (by reverse transcription [RT]-qPCR), with P. falciparum responsible for the majority (97%) of positive cases. Thus, exclusive reliance on microscopy in endemic areas may impede control efforts resulting from false negatives, underscoring the necessity for enhanced training and advocating for high-throughput molecular testing such as RT-qPCR or qPCR at referral centers to address limitations.

Molecular speciation of Plasmodium and multiplicity of P. falciparum infection in the Central region of Ghana

Malaria is endemic in the Central region of Ghana, however, the ecological and the seasonal variations of Plasmodium population structure and the intensity of malaria transmission in multiple sites in the region have not been explored. In this cross-sectional study, five districts in the region were involved. The districts were Agona Swedru, Assin Central and Gomoa East (representing the forest zone) and Abura-Asebu-Kwamankese and Cape Coast representing the coastal zone. Systematically, blood samples were collected from patients with malaria. The malaria status was screened with a rapid diagnostic test (RDT) kit (CareStart manufactured by Access Bio in Somerset, USA) and the positive ones confirmed microscopically. Approximately, 200 μL of blood was used to prepare four dried blood spots of 50μL from each microscopy positive sample. The Plasmodium genome was sequenced at the Malaria Genome Laboratory (MGL) of Wellcome Sanger Institute (WSI), Hinxton, UK. The single nucleotide polymorphisms (SNPs) in the parasite mitochondria (PfMIT:270) core genome aided the species identification of Plasmodium. Subsequently, the complexity of infection (COI) was determined using the complexity of infection likelihood (COIL) computational analysis. In all, 566 microscopy positive samples were sequenced. Of this number, Plasmodium genome was detected in 522 (92.2%). However, whole genome sequencing was successful in 409/522 (72.3%) samples. In total, 516/522 (98.8%) of the samples contained P. falciparum mono-infection while the rest (1.2%) were either P. falciparum/P. ovale (Pf/Po) (n = 4, 0.8%) or P. falciparum/P. malariae/P. vivax (Pf/Pm/Pv) mixed-infection (n = 2, 0.4%). All the four Pf/Po infections were identified in samples from the Assin Central municipality whilst the two Pf/Pm/Pv triple infections were identified in Abura-Asebu-Kwamankese district and Cape Coast metropolis. Analysis of the 409 successfully sequenced genome yielded between 1-6 P. falciparum clones per individual infection. The overall mean COI was 1.78±0.92 (95% CI: 1.55-2.00). Among the study districts, the differences in the mean COI between ecological zones (p = 0.0681) and seasons (p = 0.8034) were not significant. However, regression analysis indicated that the transmission of malaria was more than twice among study participants aged 15-19 years (OR = 2.16, p = 0.017) and almost twice among participants aged over 60 years (OR = 1.91, p = 0.021) compared to participants between 20-59 years. Between genders, mean COI was similar except in Gomoa East where females recorded higher values. In conclusion, the study reported, for the first time, P. vivax in Ghana. Additionally, intense malaria transmission was found to be higher in the 15-19 and > 60 years, compared to other age groups. Therefore, active surveillance for P. vivax in Ghana and enhanced malaria control measures in the 15-19 year group years and those over 60 years are recommended.

Dynamics of IgG antibody response against Plasmodium antigens among Nigerian infants and young children

Background

Plasmodium falciparum malaria is a leading cause of child mortality in Nigeria. Neonates are born with maternal antibodies from placental transfer which may protect against malaria infection in the first months of life. The IgG dynamics of the transition from passively transferred antimalarial antibodies to actively acquired IgG from natural exposure have not been well elucidated.

Methods

Blood samples collected during a 2018 Nigeria nationwide HIV/AIDS household survey were available for 9,443 children under 5 years of age, with a subset of infants under 2 months of age having maternal samples available (n=41). Samples were assayed for the P. falciparum HRP2 antigen and anti-malarial IgG antibodies. LOESS regression examined the dynamics in IgG response in the first 5 years of life. Correlation with maternal IgG levels was assessed for mother/child pairs.

Results

Consistent decreases were observed in median IgG levels against all Plasmodium spp. antigen targets for the first months of life. At a population level, P. falciparum apical membrane antigen-1 (AMA1) and merozoite surface protein-1 19kD (PfMSP1) IgG decreased during the first 12 months of life before reaching a nadir, whereas IgGs to other targets only declined for the first 4 months of life. Seropositivity showed a similar decline with the lowest seropositivity against AMA1 and PfMSP1 at 10-12 months, though remaining above 50% during the first 2 years of life in higher transmission areas. No protective association was observed between IgG positivity and P. falciparum infection in infants. Maternal antibody levels showed a strong positive correlation with infant antibody levels for all P. falciparum antigens from birth to 2 months of age, but this correlation was lost by 6 months of age.

Discussion

Maternally transferred anti-malarial IgG antibodies rapidly decline during the first 6 months of life, with variations among specific antigens and malaria transmission intensity. From 3-23 months of age, there was a wide range in IgG levels for the blood-stage antigens indicating high individual variation in antibody production as children are infected with malaria. Non-falciparum species-specific antigens showed similar patterns in waning immunity and correlation with paired mother's IgG levels compared to P. falciparum antigens.