Clinical evaluation of commercial SARS-CoV-2 serological assays in a malaria endemic setting.

The levels of immune response to SARS-CoV-2 infection or vaccination are poorly understood in African populations and is complicated by cross-reactivity to endemic pathogens as well as differences in host responsiveness. To begin to determine the best approach to minimize false positive antibody levels to SARS-CoV-2 in an African population, we evaluated three commercial assays, namely Bio-Rad Platelia SARS-CoV-2 Total Antibody (Platelia), Quanterix Simoa Semi-Quantitative SARS-CoV-2 IgG Antibody Test (anti-Spike), and the GenScript cPass™ SARS-CoV-2 Neutralization Antibody Detection Kit (cPass) using samples collected in Mali in West Africa prior to the emergence of SARS-CoV-2. A total of one hundred samples were assayed. The samples were categorized in two groups based on the presence or absence of clinical malaria. Overall, thirteen out of one hundred (13/100) samples were false positives with the Bio-Rad Platelia assay and one of the same one hundred (1/100) was a false positive with the anti-Spike IgG Quanterix assay. None of the samples tested with the GenScript cPass assay were positive. False positives were more common in the clinical malaria group, 10/50 (20%) vs. the non-malaria group 3/50 (6%); p = 0.0374 using the Bio-Rad Platelia assay. Association between false positive results and parasitemia by Bio-Rad remained evident, after adjusting for age and sex in multivariate analyses. In summary, the impact of clinical malaria on assay performance appears to depend on the assay and/or antigen being used. A careful evaluation of any given assay in the local context is a prerequisite for reliable serological assessment of anti-SARS-CoV-2 humoral immunity.

Ex-vivo Sensitivity of Plasmodium falciparum to Common Anti-malarial Drugs: The Case of Kéniéroba, a Malaria Endemic Village in Mali.

BACKGROUND: In 2006, the National Malaria Control Program in Mali recommended artemisinin-based combination therapy as the first-line treatment for uncomplicated malaria. Since the introduction of artemisinin-based combination therapy, few reports are available on the level of resistance of Plasmodium falciparum to the most common anti-malarial drugs in Mali. METHODS: From 2016 to 2017, we assessed the ex-vivo drug sensitivity of P. falciparum isolates in Kéniéroba, a village located in a rural area of southern Mali. We collected P. falciparum isolates from malaria-infected children living in Kéniéroba. The isolates were tested for ex-vivo sensitivity to commonly used anti-malarial drugs, namely chloroquine, quinine, amodiaquine, mefloquine, lumefantrine, dihydroartermisinin, and piperaquine. We used the 50% inhibitory concentration determination method, which is based on the incorporation of SYBR® Green into the parasite's genetic material. RESULTS: Plasmodium falciparum isolates were found to have a reduced ex-vivo sensitivity to quinine (25.7%), chloroquine (12.2%), amodiaquine (2.7%), and mefloquine (1.3%). In contrast, the isolates were 100% sensitive to lumefantrine, dihydroartermisinin, and piperaquine. A statistically significant correlation was found between 50% inhibitory concentration values of quinine and amodiaquine (r = 0.80; p < 0.0001). CONCLUSIONS: Plasmodium falciparum isolates were highly sensitive to dihydroartermisinin, lumefantrine, and piperaquine and less sensitive to amodiaquine (n = 2), mefloquine (n = 1), and quinine (n = 19). Therefore, our data support the previously reported increasing trend in chloroquine sensitivity in Mali.

A comprehensive analysis of drug resistance molecular markers and Plasmodium falciparum genetic diversity in two malaria endemic sites in Mali.

BACKGROUND: Drug resistance is one of the greatest challenges of malaria control programme in Mali. Recent advances in next-generation sequencing (NGS) technologies provide new and effective ways of tracking drug-resistant malaria parasites in Africa. The diversity and the prevalence of Plasmodium falciparum drug-resistance molecular markers were assessed in Dangassa and Nioro-du-Sahel in Mali, two sites with distinct malaria transmission patterns. Dangassa has an intense seasonal malaria transmission, whereas Nioro-du-Sahel has an unstable and short seasonal malaria transmission. METHODS: Up to 270 dried blood spot samples (214 in Dangassa and 56 in Nioro-du-Sahel) were collected from P. falciparum positive patients in 2016. Samples were analysed on the Agena MassARRAY® iPLEX platform. Specific codons were targeted in Pfcrt, Pfmdr1, Pfdhfr, and Pfdhps, Pfarps10, Pfferredoxin, Pfexonuclease and Pfmdr2 genes. The Sanger's 101-SNPs-barcode method was used to assess the genetic diversity of P. falciparum and to determine the parasite species. RESULTS: The Pfcrt_76T chloroquine-resistance genotype was found at a rate of 64.4% in Dangassa and 45.2% in Nioro-du-Sahel (p = 0.025). The Pfdhfr_51I-59R-108N pyrimethamine-resistance genotype was 14.1% and 19.6%, respectively in Dangassa and Nioro-du-Sahel. Mutations in the Pfdhps_S436-A437-K540-A581-613A sulfadoxine-resistance gene was significantly more prevalent in Dangassa as compared to Nioro-du-Sahel (p = 0.035). Up to 17.8% of the isolates from Dangassa vs 7% from Nioro-du-Sahel harboured at least two codon substitutions in this haplotype. The amodiaquine-resistance Pfmdr1_N86Y mutation was identified in only three samples (two in Dangassa and one in Nioro-du-Sahel). The lumefantrine-reduced susceptibility Pfmdr1_Y184F mutation was found in 39.9% and 48.2% of samples in Dangassa and Nioro-du-Sahel, respectively. One piperaquine-resistance Exo_E415G mutation was found in Dangassa, while no artemisinin resistance genetic-background were identified. A high P. falciparum diversity was observed, but no clear genetic aggregation was found at either study sites. Higher multiplicity of infection was observed in Dangassa with both COIL (p = 0.04) and Real McCOIL (p = 0.02) methods relative to Nioro-du-Sahel. CONCLUSIONS: This study reveals high prevalence of chloroquine and pyrimethamine-resistance markers as well as high codon substitution rate in the sulfadoxine-resistance gene. High genetic diversity of P. falciparum was observed. These observations suggest that the use of artemisinins is relevant in both Dangassa and Nioro-du-Sahel.

Plasmodium falciparum clearance rates in response to artesunate in Malian children with malaria: effect of acquired immunity.

BACKGROUND: Artemisinin resistance, a long parasite clearance half-life in response to artemisinin, has been described in patients with Plasmodium falciparum malaria in southeast Asia. Few baseline half-lives have been reported from Africa, where artemisinins were recently introduced. METHODS: We treated P. falciparum malaria in 215 Malian children aged 0.5-15 years with artesunate (0, 24, 48 hours) and amodiaquine (72, 96, 120 hours). We estimated half-life by measuring parasite density every 6 hours until undetectable and evaluated the effects of age, sex, ethnicity, and red blood cell (RBC) polymorphisms on half-life. We quantified the proportion of parasitized RBCs recognized by autologous immunoglobulin G (IgG). RESULTS: The geometric mean half-life was 1.9 hours (95% confidence interval, 1.8-2.0) and did not correlate with parasite ex vivo susceptibility to artemisinins. In a linear model accounting for host factors, half-life decreased by 4.1 minutes for every 1-year increase in age. The proportion of parasitized RBCs recognized by IgG correlated inversely with half-life (r = -0.475; P = .0006). CONCLUSIONS: Parasite clearance in response to artesunate is faster in Mali than in southeast Asia. IgG responses to parasitized RBCs shorten half-life and may influence this parameter in areas where age is not an adequate surrogate of immunity and correlates of parasite-clearing immunity have not been identified. CLINICAL TRIALS REGISTRATION: NCT00669084.

[Prevalence of maternal and placental malaria and of neonatal low birth weight in a semi-urban area of Bamako (Mali)]. / Prévalence du paludisme maternel, placentaire et du petit poids de naissance au cours du travail d'accouchement et en post-partum en milieu périurbain à Bamako (Mali).

In 2006, the Malian government established a program for free insecticide-treated net (ITNs) distribution during antenatal care visit (ANC) and intermittent preventive treatment during pregnancy with sulfadoxine-pyrimethamine (IPTp-SP) for pregnant women. In March to November of 2009, we conducted a cross-sectional study in peri-urban areas of Bamako, Mali to determine the malaria prevalence among pregnant women and their newborn children in the context of this policy. We included 379 pregnant women aged 15 to 45 years. At delivery, malaria was diagnosed using peripheral thick smears in mothers and newborns, as well as umbilical cord blood and placental blood. The prevalence of Plasmodium falciparum malaria was 2.4, 1.6 and 0.5% respectively in mother, placenta and cord samples; we observed a low birth weight rate of 12.1%. Approximately 77% of our parturient were housewives. The illiteracy rate among this group was 72.3%. Of the 379 women, 73% had at least three prenatal visits, 83% had received at least one free ITNs and 72% had received IPTp-SP during antenatal visit. Among them, 81% claimed to have complied with IPTp-SP. No congenital malaria was found. The prevalence of malaria in both mother and newborn has show a significant decrease in Bamako, compared with previous studies before the implementation of IPTp-SP policy in Mali. A high rate of coverage and use of IPTp-SP and ITNs correlate with lower malaria prevalence in pregnant women.