Genomic investigation of atypical malaria cases in Kanel, northern Senegal.

BACKGROUND: The diagnosis of malaria cases in regions where the malaria burden has decreased significantly and prevalence is very low is more challenging, in part because of reduced clinical presumption of malaria. The appearance of a cluster of malaria cases with atypical symptoms in Mbounguiel, a village in northern Senegal where malaria transmission is low, in September 2018 exemplifies this scenario. The collaboration between the National Malaria Control Programme (NMCP) at the Senegal Ministry of Health and the Laboratory of Parasitology and Mycology at Cheikh Anta Diop University worked together to evaluate this cluster of malaria cases using molecular and serological tools. METHODS: Malaria cases were diagnosed primarily by rapid diagnostic test (RDT), and confirmed by photo-induced electron transfer-polymerase chain reaction (PET-PCR). 24 single nucleotide polymorphisms (SNPs) barcoding was used for Plasmodium falciparum genotyping. Unbiased metagenomic sequencing and Luminex-based multi-pathogen antibody and antigen profiling were used to assess exposure to other pathogens. RESULTS: Nine patients, of 15 suspected cases, were evaluated, and all nine samples were found to be positive for P. falciparum only. The 24 SNPs molecular barcode showed the predominance of polygenomic infections, with identifiable strains being different from one another. All patients tested positive for the P. falciparum antigens. No other pathogenic infection was detected by either the serological panel or metagenomic sequencing. CONCLUSIONS: This work, undertaken locally within Senegal as a collaboration between the NMCP and a research laboratory at University of Cheikh Anta Diop (UCAD) revealed that a cluster of malaria cases were caused by different strains of P. falciparum. The public health response in real time demonstrates the value of local molecular and genomics capacity in affected countries for disease control and elimination.

Genetic evidence for imported malaria and local transmission in Richard Toll, Senegal.

BACKGROUND: Malaria elimination efforts can be undermined by imported malaria infections. Imported infections are classified based on travel history. METHODS: A genetic strategy was applied to better understand the contribution of imported infections and to test for local transmission in the very low prevalence region of Richard Toll, Senegal. RESULTS: Genetic relatedness analysis, based upon molecular barcode genotyping data derived from diagnostic material, provided evidence for both imported infections and ongoing local transmission in Richard Toll. Evidence for imported malaria included finding that a large proportion of Richard Toll parasites were genetically related to parasites from Thiès, Senegal, a region of moderate transmission with extensive available genotyping data. Evidence for ongoing local transmission included finding parasites of identical genotype that persisted across multiple transmission seasons as well as enrichment of highly related infections within the households of non-travellers compared to travellers. CONCLUSIONS: These data indicate that, while a large number of infections may have been imported, there remains ongoing local malaria transmission in Richard Toll. These proof-of-concept findings underscore the value of genetic data to identify parasite relatedness and patterns of transmission to inform optimal intervention selection and placement.

An innovative diagnostic technology for the codon mutation C580Y in kelch13 of Plasmodium falciparum with MinION nanopore sequencer.

BACKGROUND: The recent spread of artemisinin (ART)-resistant Plasmodium falciparum represents an emerging global threat to public health. In Southeast Asia, the C580Y mutation of kelch13 (k13) is the dominant mutation of ART-resistant P. falciparum. Therefore, a simple method for the detection of C580Y mutation is urgently needed to enable widespread routine surveillance in the field. The aim of this study is to develop a new diagnostic procedure for the C580Y mutation using loop-mediated isothermal amplification (LAMP) combined with the MinION nanopore sequencer. RESULTS: A LAMP assay for the k13 gene of P. falciparum to detect the C580Y mutation was successfully developed. The detection limit of this procedure was 10 copies of the reference plasmid harboring the k13 gene within 60 min. Thereafter, amplicon sequencing of the LAMP products using the MinION nanopore sequencer was performed to clarify the nucleotide sequences of the gene. The C580Y mutation was identified based on the sequence data collected from MinION reads 30 min after the start of sequencing. Further, clinical evaluation of the LAMP assay in 34 human blood samples collected from patients with P. falciparum malaria in Indonesia revealed a positive detection rate of 100%. All LAMP amplicons of up to 12 specimens were simultaneously sequenced using MinION. The results of sequencing were consistent with those of the conventional PCR and Sanger sequencing protocol. All procedures from DNA extraction to variant calling were completed within 3 h. The C580Y mutation was not found among these 34 P. falciparum isolates in Indonesia. CONCLUSIONS: An innovative method combining LAMP and MinION will enable simple, rapid, and high-sensitivity detection of the C580Y mutation of P. falciparum, even in resource-limited situations in developing countries.

Use of a Dual-Antigen Rapid Diagnostic Test to Screen Children for Severe Plasmodium falciparum Malaria in a High-Transmission, Resource-Limited Setting.

BACKGROUND: In rural areas, many patients with malaria seek care at peripheral health facilities or community case management programs. While this strategy is effective for the management of uncomplicated malaria, severe malaria necessitates prompt detection and referral to facilities with adequate resources. METHODS: In this prospective, observational cohort study, we assessed the accuracy of a dual-band (histidine-rich protein-2/pan-lactate dehydrogenase [HRP2/pLDH]) rapid diagnostic test (RDT) to differentiate uncomplicated from severe malaria. We included children aged <12 years who presented to a rural clinic in western Uganda with a positive HRP2 or HRP2/pLDH RDT. We estimated the test characteristics of a dual-antigen (HRP2+/pLDH+) band positive RDT compared to World Health Organization-defined clinical and laboratory criteria to detect severe malaria. RESULTS: A total of 2678 children underwent testing for malaria with an RDT, and 83 (9.0%) satisfied criteria for severe malaria. The sensitivity and specificity of a HRP2+/pLDH+ result for severe malaria was 97.6% (95% confidence interval [CI], 90.8%-99.6%) and 75.6% (95% CI, 73.8%-77.4%), respectively. An HRP2+/pLDH+ result was significantly more sensitive (97.6% vs 68.7%, P < .001) for the detection of severe malaria compared to algorithms that incorporate screening for danger signs. CONCLUSIONS: A positive dual-antigen (HRP2/pLDH) RDT has higher sensitivity than the use of clinical manifestations to detect severe malaria, making it a promising tool in the triage of children with malaria in low-resource settings. Additional work is needed to operationalize diagnostic and treatment algorithms that include dual-antigen RDTs to avoid over referral.

Multigenomic Delineation of Plasmodium Species of the Laverania Subgenus Infecting Wild-Living Chimpanzees and Gorillas.

Plasmodium falciparum, the major cause of malaria morbidity and mortality worldwide, is only distantly related to other human malaria parasites and has thus been placed in a separate subgenus, termed Laverania Parasites morphologically similar to P. falciparum have been identified in African apes, but only one other Laverania species, Plasmodium reichenowi from chimpanzees, has been formally described. Although recent studies have pointed to the existence of additional Laverania species, their precise number and host associations remain uncertain, primarily because of limited sampling and a paucity of parasite sequences other than from mitochondrial DNA. To address this, we used limiting dilution polymerase chain reaction to amplify additional parasite sequences from a large number of chimpanzee and gorilla blood and fecal samples collected at two sanctuaries and 30 field sites across equatorial Africa. Phylogenetic analyses of more than 2,000 new sequences derived from the mitochondrial, nuclear, and apicoplast genomes revealed six divergent and well-supported clades within the Laverania parasite group. Although two of these clades exhibited deep subdivisions in phylogenies estimated from organelle gene sequences, these sublineages were geographically defined and not present in trees from four unlinked nuclear loci. This greatly expanded sequence data set thus confirms six, and not seven or more, ape Laverania species, of which P. reichenowi, Plasmodium gaboni, and Plasmodium billcollinsi only infect chimpanzees, whereas Plasmodium praefalciparum, Plasmodium adleri, and Pladmodium blacklocki only infect gorillas. The new sequence data also confirm the P. praefalciparum origin of human P. falciparum.

Changing Trends in P. falciparum Burden, Immunity, and Disease in Pregnancy.

BACKGROUND: Prevention of reinfection and resurgence is an integral component of the goal to eradicate malaria. However, the adverse effects of malaria resurgences are not known. METHODS: We assessed the prevalence of Plasmodium falciparum infection among 1819 Mozambican women who delivered infants between 2003 and 2012. We used microscopic and histologic examination and a quantitative polymerase-chain-reaction (qPCR) assay, as well as flow-cytometric analysis of IgG antibody responses against two parasite lines. RESULTS: Positive qPCR tests for P. falciparum decreased from 33% in 2003 to 2% in 2010 and increased to 6% in 2012, with antimalarial IgG antibody responses mirroring these trends. Parasite densities in peripheral blood on qPCR assay were higher in 2010-2012 (geometric mean [±SD], 409±1569 genomes per microliter) than in 2003-2005 (44±169 genomes per microliter, P=0.02), as were parasite densities in placental blood on histologic assessment (50±39% of infected erythrocytes vs. 4±6%, P<0.001). The malaria-associated reduction in maternal hemoglobin levels was larger in 2010-2012 (10.1±1.8 g per deciliter in infected women vs. 10.9±1.7 g per deciliter in uninfected women; mean difference, -0.82 g per deciliter; 95% confidence interval [CI], -1.39 to -0.25) than in 2003-2005 (10.5±1.1 g per deciliter vs. 10.6±1.5 g per deciliter; difference, -0.12 g per deciliter; 95% CI, -0.67 to 0.43), as was the reduction in birth weight (2863±440 g in women with past or chronic infections vs. 3070±482 g in uninfected women in 2010-2012; mean difference, -164.5 g; 95% CI, -289.7 to -39.4; and 2994±487 g vs. 3117±455 g in 2003-2005; difference, -44.8 g; 95% CI, -139.1 to 49.5). CONCLUSIONS: Antimalarial antibodies were reduced and the adverse consequences of P. falciparum infections were increased in pregnant women after 5 years of a decline in the prevalence of malaria. (Funded by Malaria Eradication Scientific Alliance and others.).

Parasite burden and severity of malaria in Tanzanian children.

BACKGROUND: Severe Plasmodium falciparum malaria is a major cause of death in children. The contribution of the parasite burden to the pathogenesis of severe malaria has been controversial. METHODS: We documented P. falciparum infection and disease in Tanzanian children followed from birth for an average of 2 years and for as long as 4 years. RESULTS: Of the 882 children in our study, 102 had severe malaria, but only 3 had more than two episodes. More than half of first episodes of severe malaria occurred after a second infection. Although parasite levels were higher on average when children had severe rather than mild disease, most children (67 of 102) had high-density infection (>2500 parasites per 200 white cells) with only mild symptoms before severe malaria, after severe malaria, or both. The incidence of severe malaria decreased considerably after infancy, whereas the incidence of high-density infection was similar among all age groups. Infections before and after episodes of severe malaria were associated with similar parasite densities. Nonuse of bed nets, placental malaria at the time of a woman's second or subsequent delivery, high-transmission season, and absence of the sickle cell trait increased severe-malaria risk and parasite density during infections. CONCLUSIONS: Resistance to severe malaria was not acquired after one or two mild infections. Although the parasite burden was higher on average during episodes of severe malaria, a high parasite burden was often insufficient to cause severe malaria even in children who later were susceptible. The diverging rates of severe disease and high-density infection after infancy, as well as the similar parasite burdens before and after severe malaria, indicate that naturally acquired resistance to severe malaria is not explained by improved control of parasite density. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Effect of supplementation with zinc and other micronutrients on malaria in Tanzanian children: a randomised trial.

BACKGROUND: It is uncertain to what extent oral supplementation with zinc can reduce episodes of malaria in endemic areas. Protection may depend on other nutrients. We measured the effect of supplementation with zinc and other nutrients on malaria rates. METHODS AND FINDINGS: In a 2×2 factorial trial, 612 rural Tanzanian children aged 6-60 months in an area with intense malaria transmission and with height-for-age z-score≤-1.5 SD were randomized to receive daily oral supplementation with either zinc alone (10 mg), multi-nutrients without zinc, multi-nutrients with zinc, or placebo. Intervention group was indicated by colour code, but neither participants, researchers, nor field staff knew who received what intervention. Those with Plasmodium infection at baseline were treated with artemether-lumefantrine. The primary outcome, an episode of malaria, was assessed among children reported sick at a primary care clinic, and pre-defined as current Plasmodium infection with an inflammatory response, shown by axillary temperature ≥37.5°C or whole blood C-reactive protein concentration ≥ 8 mg/L. Nutritional indicators were assessed at baseline and at 251 days (median; 95% reference range: 191-296 days). In the primary intention-to-treat analysis, we adjusted for pre-specified baseline factors, using Cox regression models that accounted for multiple episodes per child. 592 children completed the study. The primary analysis included 1,572 malaria episodes during 526 child-years of observation (median follow-up: 331 days). Malaria incidence in groups receiving zinc, multi-nutrients without zinc, multi-nutrients with zinc and placebo was 2.89/child-year, 2.95/child-year, 3.26/child-year, and 2.87/child-year, respectively. There was no evidence that multi-nutrients influenced the effect of zinc (or vice versa). Neither zinc nor multi-nutrients influenced malaria rates (marginal analysis; adjusted HR, 95% CI: 1.04, 0.93-1.18 and 1.10, 0.97-1.24 respectively). The prevalence of zinc deficiency (plasma zinc concentration <9.9 µmol/L) was high at baseline (67% overall; 60% in those without inflammation) and strongly reduced by zinc supplementation. CONCLUSIONS: We found no evidence from this trial that zinc supplementation protected against malaria. TRIAL REGISTRATION: ClinicalTrials.gov NCT00623857

Considerations on the use of adjunct red blood cell exchange transfusion in the treatment of severe Plasmodium falciparum malaria.

BACKGROUND: Travelers returning to the United States from malaria-endemic areas are at increased risk of a potentially fatal infection from Plasmodium falciparum, which requires prompt and aggressive treatment. STUDY DESIGN AND METHODS: Described is a case of a 7-year-old boy who was infected by P. falciparum while in Africa and developed features of severe infection, including hyperparasitemia, altered neurologic status, and malarial hepatitis. RESULTS: A single automated erythrocytapheresis procedure reduced parasitemia from 14% to less than 1%. Along with intravenous quinidine, this reduced parasite level was maintained throughout the hospitalization and the patient recovered. CONCLUSION: Exchange transfusion (ET) is an effective adjunct therapy to reduce the parasite load in cases of severe P. falciparum malaria. When performed in certain defined settings, the benefits can outweigh the risks of the procedure. Discussed are the medical and technical considerations on the use of adjunctive ET for severe P. falciparum infection and a review of the literature of the use of adjunct ET in the treatment of severe P. falciparum malaria.

In-hospital risk estimation in children with malaria--early predictors of morbidity and mortality.

BACKGROUND: Rapid diagnosis and adequate therapy are crucial to prevent development of severe disease and death in children suffering from malaria. A reliable but easy system for disease severity assessment would help to fast track seriously ill children and provide suitable therapies for different patient groups. OBJECTIVES: To examine risk factors and appropriate scoring systems in children suffering from malaria for outcome in terms of morbidity and mortality. METHODS: A prospective, consecutive study in children admitted to the Muhimbili Medical Centre in Dar es Salaam was conducted to evaluate risk factors and test appropriate scoring systems. The simplified Multi-Organ Dysfunction Score (sMODS), a severity of disease classification consisting mainly of clinical data, was applied. Chosen outcome parameters were morbidity and mortality. Results were compared to those obtained from the World Health Organisation (WHO) classification of severe malaria, the Blantyre Coma Scale (BCS) and selected single clinical parameters. RESULTS: Seventy-five children were recruited into the study. Mean age was 28 months ranging from 6 months to 8 years. 'Severe Malaria', according to WHO criteria was evident in 57 patients (76%). Mean sMODS on admission was 15.6 +/- 2. Seven patients (9%) died. Among single symptoms, impaired consciousness and respiratory distress predicted both, fatal outcome and morbidity. In terms of scoring systems, the sMODS correlated with both outcome parameters. In comparison, the WHO criteria did not correlate with any of the two parameters, the BCS correlated with mortality only. CONCLUSION: In our study, sMODS has been shown to represent a useful quantitative approach towards disease severity classification in resource poor settings and can be used for risk estimation in children suffering from malaria in terms of both morbidity and mortality.

[Polymorphisms of the pfmdr1 gene in field samples of Plasmodium falciparum and their association with therapeutic response to antimalarial drugs and severe malaria in Colombia]. / Polimorfismos del gen pfmdr1 en muestras clínicas de Plasmodium falciparum y su relación con la respuesta terapéutica a antipalúdicos y paludismo grave en Colombia.

INTRODUCTION: The pfmdr1 gene of Plasmodium falciparum has been described as a gene conferring resistance to several antimalarial drugs. In particular, polymorphisms on specific codons have been associated with resistance and treatment failure with cloroquine, amodiaquine and mefloquine. However, the role of these polymorphisms in treatment response to antimalarials remains unexplored in Colombia. Furthermore, the relationship of these polymorphisms to severe malaria is unknown. OBJECTIVE: This work studied the association of the Asn 86Tyr and Asp1246Tyr pfmdr1 polymorphisms with response to cloroquine, amodiaquine and mefloquine treatment in three municipalities of Antioquia, and severe malaria cases from the municipality Tumaco. MATERIALS AND METHODS: The polymorphisms were assessed by nucleic acid amplification followed by restriction length polymorphism analysis. RESULTS: The wild-type codon Asn 86 was detected in 97% of the clinical samples from the treatment response study. No association was detected between this polymorphism and treatment failure to the three antimalarials administered. The 1246Tyr polymorphism was detected with a higher frequency in the samples from Antioquia 92% (130/141) than in those from Tumaco 22% (20/89). However, again, no association was found between the presence of a specific polymorphism and the presence of severe malaria in the municipality of Tumaco. CONCLUSIONS: The 86Tyr and 1246Tyr polymorphisms of the pfmdr1 gene are not useful as predictors of treatment failure or severe malaria in the municipalities studied. In addition, we report for the first time, the presence of the mutant codon 86Tyr in field samples in South America.

Changes in var gene mRNA levels during erythrocytic development in two phenotypically distinct Plasmodium falciparum parasites.

BACKGROUND: The var multigene family encodes PfEMP1, which are expressed on the surface of infected erythrocytes and bind to various host endothelial receptors. Antigenic variation of PfEMP1 plays a key role in malaria pathogenesis, a process partially controlled at the level of var gene transcription. Transcriptional levels, throughout the intra-erythrocytic cycle, of 59 var genes of the NF54 clone were measured simultaneously by quantitative real-time PCR. The timing of var transcript abundance, the number of genes transcribed and whether transcripts were correctly spliced for protein expression were determined. Two parasite populations were studied; an unselected population of NF54 and a selected population, NF54VAR2CSA, to compare both the transcription of var2csa and the expression pattern of the corresponding protein. METHODS: Synchronized parasites were harvested at different time points along the 48 hours intra-erythrocytic cycle for extraction of RNA and for analysis of expression of variant surface antigens by flow cytometry. Total RNA from each parasite sample was extracted and cDNA synthesized. Quantitative real-time PCR was performed using gene-specific primers for all var genes. Samples for flow cytometry were labelled with rabbit IgG targeting DBL5epsilon of VAR2CSA and serum IgG from malaria-exposed men and pregnant women. RESULTS: var transcripts were detected at all time points of the intra-erythrocytic cycle by quantitative real-time PCR, although transcription peaked in ring-stage parasites. There was no difference in the timing of appearance of group A, B or C transcripts, and dominant and subdominant var transcripts appeared to be correctly spliced at all time points. VAR2CSA appeared on the surface of infected erythrocytes 16 hours after invasion, consistent with previous studies of other PfEMP1. Transcription of the pseudogene var1csa could not be detected in NF54VAR2CSA cells. CONCLUSION: The optimal sampling point for analysis of var transcripts using quantitative real-time PCR is the ring-stage, which is encouraging for the analysis of fresh clinical isolates. The data presented here indicate that there is no promiscuous transcription of var genes at the individual cell level and that it is possible to correlate dominant transcripts with adhesion phenotype and clinical markers of malaria severity.

Relative levels of IL4 and IFN-gamma in complicated malaria: association with IL4 polymorphism and peripheral parasitemia.

Functional IL4-590 C/T polymorphisms and the relative amounts of IL4 and IFN-gamma were investigated in relation to severity of malaria in 110 and 169 Thai patients with complicated and uncomplicated malaria, respectively. The plasma IL4 and IFN-gamma levels were determined by ELISA and the IL4-590 C/T polymorphisms were genotyped. The IFN-gamma levels were significantly elevated in patients with complicated malaria in the initial stage of the disease before treatment compared to the levels found with uncomplicated malaria (231pg/ml versus 150pg/ml, p=0.0029), while the IL4 levels were significantly elevated 7 days after treatment (167pg/ml versus 81pg/ml, p=0.0003). Our study did not reveal any association between the IL4-590 C/T transition and the severity of malaria. However, a significant difference in the IL4 to IFN-gamma ratio between patients with complicated and uncomplicated malaria was observed only in patients with IL4-590 T allele homozygosity (geometric mean: 0.321 versus 0.613, p=0.0087 for TT allele). A significant inverse correlation between IL4 to IFN-gamma ratio and peripheral parasitemia was observed only in complicated malaria patients carrying TT genotype (r=-0.283, p=0.046). These results suggest that the IL4-590 C/T polymorphism may play a role in the balance between IL4 and IFN-gamma, as well as in the control of parasitemia, which in turn may alter the severity of malaria.

Differences in presentation of severe malaria in urban and rural Gabon.

There are rare comparative studies of the clinical and laboratory features of severe and moderate malaria, including predictors of poor outcome, in rural and urban areas for regions of high malaria transmission. We therefore studied 2,235 children hospitalized for malaria in a rural (Lambaréné) and an urban (Libreville) area in Gabon between January 2001 and December 2002. From children screened, 33% and 48% were hospitalized for malaria in Libreville and Lambaréné, respectively (P < 0.001). Two malaria clinical groups were identified according to the World Health Organization 2000 classification of severe malaria. In both areas, severe malaria was characterized by a high proportion of severe anemia. The case fatality rate was 5-fold lower in Lambaréné than in Libreville (1% versus 5%; P < 0.0001). In both sites, cerebral malaria associated with respiratory distress was the most important predictor of fatal malaria (odds ratio = 10.7, 95% confidence interval = 4.8-23.8 P < 0.0001).

No variation in the prevalence of point mutations in the Pfcrt and Pfmdr1 genes in isolates from Gabonese patients with uncomplicated or severe Plasmodium falciparum malaria.

In Lambaréné (Gabon), where a high level of Plasmodium falciparum resistance to chloroquine has been reported, we assessed the relationship between polymorphisms in the P. falciparum chloroquine resistance transporter (Pfcrt) and multidrug resistance-1 (Pfmdr1) genes and the clinical severity of malaria. Ninety-one and 60 P. falciparum isolates from children with uncomplicated or severe malaria were collected in 1996 and 2002, respectively. Single nucleotide mutations at codon 76 in the Pfcrt gene and at codons 86, 184, 1034, 1042, and 1246 in the Pfmdr1 gene were assessed by PCR-RFLP. All P. falciparum isolates presented the Pfcrt K76T mutation, whatever the clinical status. A high prevalence (>80%) of the Pfmdr1 86Tyr and 184Phe mutations was detected at both time points and in both clinical groups. We did not identify any specific mutation in the Pfmdr1 gene associated with the severity of disease, and the multiplicity of P. falciparum infection was also similar in both groups. Our results showed no change in the polymorphism of Pfcrt and Pfmdr1 genes in P. falciparum isolates collected in 1996 and 2002, and the severity of the disease was not associated with specific mutations neither in the Pfcrt nor in the Pfmdr1 genes in the study site.

Validation of microsatellite markers for use in genotyping polyclonal Plasmodium falciparum infections.

Genotyping methods for Plasmodium falciparum drug efficacy trials have not been standardized and may fail to accurately distinguish recrudescence from new infection, especially in high transmission areas where polyclonal infections are common. We developed a simple method for genotyping using previously identified microsatellites and capillary electrophoresis, validated this method using mixtures of laboratory clones, and applied the method to field samples. Two microsatellite markers produced accurate results for single-clone but not polyclonal samples. Four other microsatellite markers were as sensitive as, and more specific than, commonly used genotyping techniques based on merozoite surface proteins 1 and 2. When applied to samples from 15 patients in Burkina Faso with recurrent parasitemia after treatment with sulphadoxine-pyrimethamine, the addition of these four microsatellite markers to msp1 and msp2 genotyping resulted in a reclassification of outcomes that strengthened the association between dhfr 59R, an anti-folate resistance mutation, and recrudescence (P = 0.31 versus P = 0.03). Four microsatellite markers performed well on polyclonal samples and may provide a valuable addition to genotyping for clinical drug efficacy studies in high transmission areas.

[Malaria in mangrove areas of the Saloum delta (Senegal)]. / Le paludisme en zone de mangrove du delta du Saloum (Sénégal).

This study of malaria biodiversity in Senegal used an entomological approach that combined parasite surveys and clinical investigations in the mangrove area of the Saloum delta from 1996 to 1998. The parasitologic studies took place in two of the six villages in the coastal area of Palmarin (Djifère and Diakhanor) during three distinct periods: at the end of the dry season, in the middle of the rainy season, and at the end of the rainy season. The clinical investigations at the Palmarin health station took place from July 1996 through February 1998. A malaria attack was defined as the presence of malaria symptoms (including fever, headaches, sweating, and shivering) associated with plasmodic parasitemia > 3,000 trophozoites/microL of blood. All the positive thick smears were infected with Plasmodium falciparum, one also with P. falciparum, and none with P. ovale. The average plasmodic index (5.6%) classifies the delta of Saloum as a hypoendemic area. The average parasite load was estimated at 2,239 trophozoites (95% CI: 1,660-3,020) of P. falciparum per microliter of blood, and 86.9% of patients with symptoms of a malaria attack were febrile. Malaria attacks accounted for 1.9% of the total consultations, 12.2% of the presumed malaria cases, and 14.0% of the febrile subjects. The finding that malaria attacks affected all age groups confirms the weakness of anti-malaria immunity among the population of the Saloum delta. Malaria cases were more frequent at the end of the rainy season and the beginning of the dry season, periods when parasite loads were highest. In this area, which is increasingly attractive to tourists and has a quite superficial fresh water table, man-made environmental changes favor mosquito breeding sites that promote the development of An. arabiensis and An. gambiae spp, both known to be major malaria vectors. In view of the population's weak anti-malaria immunity, this situation may increase malaria transmission and could be followed by epidemics. It is therefore important to set up a functional system of epidemiological monitoring to detect any malaria outbreaks.

Duration of protection with RTS,S/AS02A malaria vaccine in prevention of Plasmodium falciparum disease in Mozambican children: single-blind extended follow-up of a randomised controlled trial.

BACKGROUND: RTS,S/AS02A is a pre-erythrocytic stage malaria vaccine that provides partial protection against infection in malaria-naive adult volunteers and hyperimmune adults. A previous report showed that this vaccine reduced risk of clinical malaria, delayed time to new infection, and reduced episodes of severe malaria over 6 months in African children. An important remaining issue is the durability of protection against clinical disease in these children. METHODS: We did a randomised, controlled, phase IIb trial of RTS,S/AS02A given at 0, 1, and 2 months in 2022 Mozambican children aged 1-4 years. We previously determined vaccine efficacy (VE) against clinical malaria in a double-blind phase that included study months 2.5-8.5 (VE(2.5-8.5)). We now report VE in a single-blind phase up to month 21 (VE(8.5-21)). The primary endpoint was time to first or only clinical episode of Plasmodium falciparum malaria (axillary temperature 37.5 degrees C and P falciparum asexual parasitaemia >2500 per microL) detected through a passive case detection system. We also determined VE for other case definitions and for episodes of severe malaria. This study is registered with the ClinicalTrials.gov identifier NCT00197041. FINDINGS: During the single-blind phase, VE(8.5-21) was 28.9% (95% CI 8.4-44.8; p=0.008). At month 21, prevalence of P falciparum infection was 29% lower in the RTS,S/AS02A group than in the control (p=0.017). Considering the entire study period, VE(2.5-21) was 35.3% (95% CI 21.6-46.6; p<0.0001) and VE(2.5-21) for severe malaria was 48.6% (95% CI 12.3-71.0; p=0.02). INTERPRETATION: These results show that RTS,S/AS02A confers partial protection in African children aged 1-4 years living in rural endemic areas against a range of clinical disease caused by P falciparum for at least 18 months, and confirm the potential of malaria vaccines to become credible control tools for public-health use.

Genetic diversity of the msp-1 locus and symptomatic malaria in south-west Nigeria.

Genetic characteristics of Plasmodium falciparum may play a role in the clinical severity of malaria infection. We have studied the association between diversity at the merozoite surface protein-1 (msp-1) locus and the severity of disease in childhood malaria in Ibadan, south-west Nigeria. Two hundred and twenty-three children (median age of 34.5 months) presenting with malaria were enrolled into the study. They comprised 53 children with asymptomatic malaria (ASM), 101 with acute uncomplicated malaria (UM) and 69 with severe malaria (SM). Genotyping of the msp-1 locus was by polymerase chain reaction. The distribution of msp-1 alleles was significantly different between the three groups. Asymptomatic malaria samples had a higher median number of alleles than the other two groups. The type of msp-1 allele detected was significantly associated with the clinical category of malaria. The absence of K1 alleles was associated with a three-fold increase risk of UM and a four-fold increased risk of SM when compared with asymptomatic malaria. The absence of MAD20 alleles was associated with a five-fold increase risk of UM and an eight-fold increase of SM. We have found an association between the msp-1 locus of P. falciparum and clinical severity of malaria in a sample of Nigerian children. Our findings show that the presence of the K1 and MAD20 alleles was significantly associated with ASM and consequently a reduced risk of developing the symptomatic disease.

Naturally acquired immunity to Plasmodium falciparum malaria in Africa.

Infection by Plasmodium falciparum parasites can lead to substantial protective immunity to malaria, and available evidence suggest that acquisition of protection against some severe malaria syndromes can be fairly rapid. Although these facts have raised hopes that the development of effective vaccines against this major cause of human misery is a realistic goal, the uncertainty regarding the antigenic targets of naturally acquired protective immunity and the immunological mechanisms involved remain major vaccine development obstacles. Nevertheless, a coherent theoretical framework of how protective immunity to P. falciparum malaria is acquired following natural exposure to the parasites is beginning to emerge, not least thanks to studies that have combined clinical and epidemiological data with basic immunological research. This framework involves IgG with specificity for clonally variant antigens on the surface of the infected erythrocytes, can explain some of the difficulties in relating particular immune responses with specificity for well-defined antigenic targets to clinical protection, and suggests a radically new approach to controlling malaria-related morbidity and mortality by immunological means.