Spatial Patterns of Plasmodium falciparum Clinical Incidence,Asymptomatic Parasite Carriage and Anopheles Density in Two Villages in Mali

Heterogeneity in malaria exposure is most readily recognized in areas with low-transmission patterns. By comparison, little research has been done on spatial patterns in malaria exposure in high-endemic settings. We determined the spatial clustering of clinical malaria incidence, asymptomatic parasite carriage, and Anopheles density in two villages in Mali exposed to low- and mesoendemic-malaria transmission. In the two study areas that were < 1 km² in size, we observed evidence for spatial clustering of Anopheles densities or malaria parasite carriage during the dry season. Anopheles density and malaria prevalence appeared associated in some of our detected hotspots. However, many households with high parasite prevalence or high Anopheles densities were located outside the identified hotspots. Our findings indicate that within small villages exposed to low- or mesoendemic-malaria transmission, spatial patterns in mosquito densities and parasite carriage are best detected in the dry season. Considering the high prevalence of parasite carriage outside detected hotspots, the suitability of the area for targeting control efforts to households or areas of more intense malaria transmission may be limited.     

Seroreactivity to a Large Panel of Field-Derived Plasmodium falciparum Apical Membrane Antigen 1 and Merozoite Surface Protein 1 Variants Reflects Seasonal and Lifetime Acquired Responses to Malaria

Parasite antigen diversity poses an obstacle to developing an effective malaria vaccine. A protein microarray containing Plasmodium falciparum apical membrane antigen 1 (AMA1, n = 57) and merozoite surface protein 1 19-kD (MSP1₁₉, n = 10) variants prevalent at a malaria vaccine testing site in Bandiagara, Mali, was used to assess changes in seroreactivity caused by seasonal and lifetime exposure to malaria. Malian adults had significantly higher magnitude and breadth of seroreactivity to variants of both antigens than did Malian children. Seroreactivity increased over the course of the malaria season in children and adults, but the difference was more dramatic in children. These results help to validate diversity-covering protein microarrays as a promising tool for measuring the breadth of antibody responses to highly variant proteins, and demonstrate the potential of this new tool to help guide the development of malaria vaccines with strain-transcending efficacy.Plasmodium falciparum uses antigenic variation to evade host immunity, including vaccine-induced immunity.^1,2 The protective immunity against P. falciparum malaria disease that is acquired after years of exposure is believed to reflect, in part, the gradual acquisition of allele-specific immune responses against a repertoire of parasite antigens, and, importantly, against diverse variants of these antigens.³ Apical membrane antigen 1 (AMA1) and merozoite surface protein 1 (MSP1) are immunogenic parasite surface antigens considered vital for erythrocyte attachment and invasion. Antibodies against these proteins are associated with protection against malaria, and several subunit AMA1 and MSP1 vaccines have been developed and tested.^1,4–6 Both AMA1 and MSP1₁₉, the C-terminus portion of the MSP1 protein used in subunit vaccines, are highly variable, with sequence diversity encoded by single nucleotide polymorphisms.^7,8 The highest prevalence of any one of the 440 AMA1 haplotypes observed from sequencing the ama1 gene among more than 1,400 field infections diagnosed during prospective incidence studies and vaccine trials was less than 4%.^1,8,9Although less extreme, MSP1₁₉ also has substantial diversity, with 17 haplotypes detected among more than 1,300 infections.⁷ Because vaccines that include dozens or hundreds of antigen variants are not feasible, malaria vaccine development would be aided by the identification of a manageable number of serodominant, cross-protective haplotypes among AMA1 and MSP1₁₉ variants. Developing such strain-transcending vaccines is hindered by the limited availability of diverse parasite antigens and the low throughput of standard assays such as enzyme-linked immunosorbent assay for measuring antibody responses.Protein microarrays offer the possibility of overcoming these obstacles to enable high throughput evaluations of seroreactivity to large numbers of antigen variants. Plasmodium falciparum proteins expressed in a cell-free Escherichia coli translation system and spotted onto microarrays are recognized by serum antibodies of persons exposed to malaria.^10–12 To date, this platform has been used to measure seroreactivity to large numbers of proteins derived from the genome of the P. falciparum reference strain 3D7.^10,12–14 To examine antibody responses to diverse variants of highly polymorphic P. falciparum antigens, we amplified, expressed and printed dozens of field-derived variants of AMA1 and MSP1₁₉ on a protein microarray.Antigen genes were amplified by polymerase chain reaction from DNA extracted from dried blood spots collected in a cohort study and an AMA1 vaccine trial in Mali, Africa. The resulting amplicons were analyzed by using the BigDye^® Terminator v3.1 Cycle Direct Sequencing Kit (Applied Biosciences, Foster City, CA).^4,8,15 Sequence contigs were compiled by using Sequencher software (Gene Codes, Ann Arbor, MI).^9,16 Sixty of the most prevalent AMA1 ectodomain haplotypes and 10 MSP1₁₉ haplotypes were selected for inclusion on the prototype protein microarray. Microarray construction has been described.¹⁷Serum samples were obtained from 18 adults 18–55 years of age enrolled in the control arm of a phase 1 trial of an AMA1-based vaccine conducted during 2004–2005 in Bandiagara, Mali.¹⁸ Similarly, serum samples were randomly obtained from 24 children 1–6 years of age enrolled in the control arm of a phase 1 trial of an AMA1-based malaria vaccine during 2006–2007 at the same site.^6,19 Bandiagara, Mali has high seasonal malaria transmission coinciding with the June–November rainy season, with entomologic inoculation rates of 50–150 infected bites/person/season.⁸ For each participant, paired serum samples from two time points corresponding to the pre-malaria (May–June) and post-malaria (December–January) seasons were probed in random order to eliminate batch and slide effects.Two microliters of serum from individual participant samples was diluted 1:200 with 10% E. coli lysate in blocking buffer and hybridized onto separate protein arrays overnight. Arrays were stained, washed, and scanned by using a Perkin-Elmer (Waltham, MA) ScanArray Express HT microarray scanner. Probing protocols have been described.^10,12,17 Fluorescence was quantified by using the ScanArray Express Suite (Perkin-Elmer). Median fluorescent intensities (MFIs) were calculated by using an adaptive capture feature to account for varying spot size, and the per-spot local background was subtracted.Raw MFIs were asinh-transformed to convert the MFI values to a Gaussian (normal) distribution, and biological variance contributed by seroreactivity to the E. coli components included in the translation protocol was subtracted by taking the average of eight empty vector, translated, negative controls (i.e., the no DNA controls). Residual non-biological variance between slides, batches, and individual arrays was corrected by using robust linear modeling (RLM) with respect to the negative and positive controls.²⁰ Asinh-transformed, RLM-scaled data were reverted to fluorescent intensities by sinh reverse-transformation and plotted on a heat map to show global trends (Figure 1).Open in a separate windowFigure 1.Heat map of seroreactivity to Plasmodium falciparum apical membrane antigen 1 (AMA1) and merozoite surface protein 1–19 (MSP1₁₉) variants. Each column represents serum from an individual Malian child or adult, or a malaria-naive North American adult, and each row represents an antigen variant. Gray, black, and red indicate low, moderate and high seroreactivity, respectively, to probed antigens. Four serial dilutions of IgG peptide were printed and probed as positive probing controls and used as a standardization parameter for robust linear model scaling as a measurement of total IgG. MFI = median fluorescent intensity.Parametric statistical hypotheses were tested on asinh-transformed, RLM-scaled data by using BioconductR (http://www.bioconductor.org/index.html, Excel (Microsoft, Redmond, WA), and SAS/STAT software (SAS Institute, Cary, NC). The magnitude of seroreactivity was measured by mean MFI using matched pair Student''s t tests (

P. falciparum malaria prevalence among blood donors in Bamako,Mali

Aim

Malaria parasite is usually transmitted to humans by Anopheles mosquitoes but it can also be transmitted through blood transfusion. Usually malaria transmission is low in African urban settings. In West Africa where the P. falciparum is the most predominant malaria species, there are limited measures to reduce the risk of blood transfusion malaria. The aim of this study was to evaluate the prevalence of P. falciparum malaria carriage among blood donors in the National Blood Center of Bamako, capital city of Mali.

The etiology of severe anemia in a village and a periurban area in Mali

Severe anemia is one of the major complications of malaria in Africa. We studied 2 populations, one in a village and the second in a periurban area in Mali, to understand the preventable factors in the disease. The 2 correlates of disease were parasitemia above 100 000 parasitized red blood cells per microliter (0.1 x 10(12)/L) and a low baseline hemoglobin level. All cases of moderate to severe anemia occurred in children under 3.2 years of age. Raising the baseline hemoglobin level and lowering peak parasitemia in infants and young children may reduce the incidence of severe anemia resulting from malarial infection.     

Malaria incidence in relation to rice cultivation in the irrigated Sahel of Mali

Seven repeated cross-sectional parasitological surveys, collecting a total of 13,912 blood samples, were carried out from September 1995 to February 1998 in three irrigated rice growing villages and three villages without irrigated agriculture in the area surrounding Niono, Mali. Parasite prevalence varied according to season and agricultural zone, but showed similar patterns for villages within the same zone. Overall, malaria prevalence was 47% in the villages without irrigated agriculture and 34% in the irrigated rice growing villages. In a village in the irrigated zone, and a village in the non-irrigated zone, 1067 and 608 children up to the age of 14 years, respectively, were followed in a passive malariological study for the period of 13 months. Fevers were attributed to malaria using a statistical method, taking into account the parasitaemia in afebrile controls from the cross-sectional surveys. The incidence of malaria fevers differed markedly between the two zones and over time. In the village in the irrigated zone, the incidence of malaria fevers was fairly constant over the year at 0.7 per 1000 children per day. In the village without irrigated agriculture, incidence was low during the dry season (at 0.6 per 1000 children per day), whereas it was high during the rainy season (at 3.2 per 1000 children per day). These results correspond well to the malaria transmission observed in a concurrent entomological survey. Rice cultivation in the semi-arid sub-Saharan environment altered the transmission pattern from seasonal to perennial, but reduced annual incidence more than two-fold.     

Clinical study using novel endoscopic system for measuring size of gastrointestinal lesion

AIM:To verify the performance of a lesion size measurement system through a clinical study.METHODS:Our proposed system,which consists of a conventional endoscope,an optical device,an optical probe,and a personal computer,generates a grid scale to measure the lesion size from an endoscopic image.The width of the grid scale is constantly adjusted according to the distance between the tip of the endoscope and lesion because the lesion size on an endoscopic image changes according to the distance.The shape of the grid scale was corrected to match the distortion of the endoscopic image.The distance was calculated using the amount of laser light reflected from the lesion through an optical probe inserted into the instrument channel of the endoscope.The endoscopist can thus measure the lesion size without contact by comparing the lesion with the size of the grid scale on the endoscopic image.(1)A basic test was performed to verify the relationship between the measurement error eM and the tilt angle of the endoscope;and(2)The sizes of three colon polyps were measured using our system during endoscopy.These sizes were immediately measured by scale after their removal.RESULTS:There was no error atα=0°.In addition,the values of eM(mean±SD)were 0.24±0.11 mm(α=10°),0.90±0.58 mm(α=20°)and 2.31±1.41mm(α=30°).According to these results,our system has been confirmed to measure accurately when the tilt angle is less than 20°.The measurement error was approximately 1 mm in the clinical study.Therefore,it was concluded that our proposed measurement system was also effective in clinical examinations.CONCLUSION:By combining simple optical equipment with a conventional endoscope,a quick and accurate system for measuring lesion size was established.     

Fc gamma Receptor IIa‐H131R Polymorphism and Malaria Susceptibility in Sympatric Ethnic Groups,Fulani and Dogon of Mali

It has been previously shown that there are some interethnic differences in susceptibility to malaria between two sympatric ethnic groups of Mali, the Fulani and the Dogon. The lower susceptibility to Plasmodium falciparum malaria seen in the Fulani has not been fully explained by genetic polymorphisms previously known to be associated with malaria resistance, including haemoglobin S (HbS), haemoglobin C (HbC), alpha‐thalassaemia and glucose‐6‐phosphate dehydrogenase (G6PD) deficiency. Given the observed differences in the distribution of FcγRIIa allotypes among different ethnic groups and with malaria susceptibility that have been reported, we analysed the rs1801274‐R131H polymorphism in the FcγRIIa gene in a study of Dogon and Fulani in Mali (n = 939). We confirm that the Fulani have less parasite densities, less parasite prevalence, more spleen enlargement and higher levels of total IgG antibodies (anti‐CSP, anti‐AMA1, anti‐MSP1 and anti‐MSP2) and more total IgE (P < 0.05) compared with the Dogon ethnic group. Furthermore, the Fulani exhibit higher frequencies of the blood group O (56.5%) compared with the Dogon (43.5%) (P < 0.001). With regard to the FcγRIIa polymorphism and allele frequency, the Fulani group have a higher frequency of the H allele (Fulani 0.474, Dogon 0.341, P < 0.0001), which was associated with greater total IgE production (P = 0.004). Our findings show that the FcγRIIa polymorphism might have an implication in the relative protection seen in the Fulani tribe, with confirmatory studies required in other malaria endemic settings.     

Plasmodium falciparum–specific IgM B cells dominate in children,expand with malaria,and produce functional IgM

IgG antibodies play a role in malaria immunity, but whether and how IgM protects from malaria and the biology of Plasmodium falciparum (Pf)–specific IgM B cells is unclear. In a Mali cohort spanning infants to adults, we conducted longitudinal analyses of Pf- and influenza-specific B cells. We found that Pf-specific memory B cells (MBCs) are disproportionally IgM⁺ and only gradually shift to IgG⁺ with age, in contrast to influenza-specific MBCs that are predominantly IgG⁺ from infancy to adulthood. B cell receptor analysis showed Pf-specific IgM MBCs are somatically hypermutated at levels comparable to influenza-specific IgG B cells. During acute malaria, Pf-specific IgM B cells expand and upregulate activation/costimulatory markers. Finally, plasma IgM was comparable to IgG in inhibiting Pf growth and enhancing phagocytosis of Pf by monocytes in vitro. Thus, somatically hypermutated Pf-specific IgM MBCs dominate in children, expand and activate during malaria, and produce IgM that inhibits Pf through neutralization and opsonic phagocytosis.     

Prévalence de Plasmodium falciparum, de l’anémie et des marqueurs moléculaires de la résistance à la chloroquine et à la sulfadoxine-pyrim éthamine chez les femmes accouchées à Fana, Mali

The aim of this study was to describe the malaria morbidity and the frequencies of molecular markers of resistance to chloroquine and sulfadoxine-pyrimethamine in pregnant women at delivery in Mali. Two hundred pregnant women have been included at the delivery clinic in Fana. The age group of 14–19 years was predominant. Fifty two per cent (52.3%: 104/200) were malaria slides positive in their peripheral blood and 15% (30/200) of the women carried parasite in their placenta. The prevalence rate of anemia was 44.5% (89/200). PCR technique was successfully performed on 16 paired samples. The frequency of the Pfcrt K76T mutants in Plasmodium falciparum infections in peripheral blood was 68.8% (11/16) and 100 % (16/16) in the placenta (p = 0.004). The frequency in peripheral blood of the DHFR N51I mutation was 12.5% (2/16) and 18.8% (3/16) in the placenta (p=0.12). The frequencies of the DHPS A437G mutants were similar in both sites 25% (4/16). No DHPS K540E and DHFR 164L mutations were found in the Fana pregnancy women samples.