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H P Beck

Publications and source records attributed to H P Beck.

At least 19 recordsLinked to original sources
PubMed2006

[Prevalence, genetic diversity and multiplicity of Plasmodium falciparum infection in school children in central Cote d'Ivoire].

A study was carried out in the village of Taabo, located in the vicinity of a large man-made lake in central Côte d'Ivoire. The objectives were (i) to determine the level of prevalence, genetic diversity and multiplicity of Plasmodiumfakiparum infection in schoolchildren and (ii) to compare the diagnostic performance of light microscopy and polymerase chain reaction (PCR). A total of 424 schoolchildren ranging in age from 5 to 15 years underwent diagnostic testing using both light microscopy of blood smears and PCR. Multiplicity of P. falciparum infection was investigated in 196 children (46.2%). The prevalence of malaria was 54.7% based on light microscopy and 83.9% based on PCR. Genotyping based on polymorphism in the length of the restriction fragment of the gene encoding the merozoite surface protein-2 (msp2) showed that 86.5% of cases involved multiple infection with a geometric mean of 3.87 genotypes per positive child. There was a strong positive correlation between multipcity of infection and parasite density in the 56-year old age group. A total of 50 genotypes including six observed for the first time were identified and classified into families with similar-sized sequence groups: 26 x FC27 (52%) and 24 x 3D7 (48%). In comparison with PCR, the sensitivity and specificity of light microscopy for diagnosis of P. falciparum was 81.3% and 88.2% respectively. Data are discussed in the light of similar studies carried out in sub-Saharan Africa and elsewhere. These findings can serve as a basis for monitoring the longterm effect of major water resource management projects on the prevalence, genetic diversity and multiplicity of P. falciparum infection.

Adolescent↗
PubMed2005

A DNA delivery system targeting dendritic cells for use in immunization against malaria: a rodent model.

DNA-based vaccination has emerged as a promising method of immunisation since the first demonstration of this technology. Improving the antibody responses is desirable for the protective efficacy and hence broad application of these vaccines. We examined the immunogenicity of a Plasmodium-based DNA vaccine that was targeted to antigen presenting cells by fusion to CTLA4. Fusion proteins comprising the extra-cellular domain of CTLA4, the hinge, CH2 and CH3 domains of human IgG1 and MSP-1 gene fragments were expressed in COS-7 cells. Three of the secreted proteins containing the mouse homologue of CTLA4 were shown to bind differently to the human B7-1 molecule expressed on THP-1 cells. Competition binding assays for two fusion proteins showed that binding was specific. When C57BL/6 mice were immunized with plasmids encoding the fusion proteins, antibodies against two denatured and one non-denatured MSP-1 gene fragments were successfully induced. The usefulness of this strategy in future studies of immunisaton against human malaria is discussed.

Animals↗
PubMed2002

Humic colloid-borne natural polyvalent metal ions: dissociation experiment.

The natural association nature of the humic colloid-borne trace elements is investigated. Rare earth elements (REE) Th and U are chosen as naturally occurring representatives and chemical homologues for actinides of different oxidation states present in nuclear waste. Tri- and tetravalent elements in two investigated Gorleben groundwaters (Gohy-532 and -2227) almost exclusively occur as humic or fulvic colloid-borne species. Their desorption behavior from colloids is examined in the unperturbed groundwater (pH approximately 8) under anaerobic conditions (Ar/1% CO2) by addition of a chelating cation exchanger resin. Particularly, the dissociation process of naturally occurring Eu(III) in the groundwater is compared with the Eu(III) desorption from its humate complex prepared with purified Aldrich humic acid in a buffered aqueous solution at pH approximately 8. The Eu(III) dissociation from the groundwater colloids is found to be considerably slower than found for the humate complex synthesized in the laboratory. This suggests that under natural aquatic conditions the Eu(III) binding in colloids is chemically different from the simple humate complexation as observed in the laboratory experiment. The colloid characterization bythe size exclusion chromatography (SEC) and the flow field-flow fractionation (FFFF) indicates that natural colloid-borne trace elements are found predominantly in colloids of larger size (>15 nm in size), while Eu(III) in its humate complex is found mainly in colloids of hydrodynamic diameters <5 nm. The slower desorption kinetics and the larger colloid size suggest that the polyvalent metal ion binding in natural humic colloids is associated to polynucleation with other co-present trace metal ions. Radiotracer experiments reveal that isotopic equilibria with the naturally colloid-borne trace elements are not attained within a period of more than 100 days, indicating irreversible binding of at least a part of colloid-borne polyvalent trace elements. The different kinetic properties of colloid-bound Eu(III) are discussed taking the aqueous speciation based on thermodynamic data into account.

Chromatography, Gel↗
PubMed2000

Genomic distribution and functional characterisation of two distinct and conserved Plasmodium falciparum var gene 5' flanking sequences.

Approximately 50 highly diverse var genes distributed throughout the haploid genome of the malaria parasite Plasmodium falciparum code for PfEMP1 variants located on the surface of infected erythrocytes. PfEMP1 is involved in cytoadherence of parasitised red blood cells and undergoes antigenic variation through differential expression of var genes. Members of the var gene family are located in chromosome-internal positions on chromosomes 4, 7, 8 and 12, and in subtelomeric regions of all chromosomes. Here we show that there are two distinct and conserved types of 5' upstream regions (var17-type and 5B1-type) of var genes, and suggest that most subtelomeric var genes are flanked by a var17-type 5' upstream sequence. In contrast, 5B1-type 5' upstream are localised to chromosomes that have been shown to contain var genes within chromosome-internal regions. Transcriptional analysis using RT-PCR revealed that var genes flanked by either type of 5' upstream sequence are transcribed in in vitro cultured trophozoite stage parasites. In addition, we have shown that the 5' flanking sequences of four different var genes are able to drive transient expression of the cat reporter gene. Our results suggest that at least the minimal regulatory sequences required for transcription of var genes are conserved among both subgroups of the var gene family. Furthermore, these sequences provide new markers for the investigation of the chromosomal organisation of var genes.

5' Untranslated Regions↗
PubMed2000

Analysis of Plasmodium falciparum infections in a village community in Northern Nigeria: determination of msp2 genotypes and parasite-specific IgG responses.

The genetic diversity of P. falciparum and multiplicity of infection has been studied in a village in Northern Nigeria at the end of the rainy season, when transmission is high. We analysed blood samples from 104 individuals aged 5-70 years by polymerase chain reaction (PCR) amplifying the gene for the merozoite surface protein MSP2 followed by genotyping based on restriction fragment length polymorphism (RFLP). 94.2% of all samples were parasite positive by PCR and over 80% of those had multiple infections. The age distribution of the average number of parasite clones present in P. falciparum infections showed an initial increase, then reached a peak multiplicity in children 8-10 years of age, and afterwards decreased significantly with age. Mean multiplicity in those 8-10-year-old children was 5.4 clones per carrier. Peak multiplicity and parasite diversity in Nigerian individuals is compared to findings from other study sites in Africa and PNG. The prevalence of IgG antibodies against the circumsporozoite protein (CSP), an indicator for malaria exposure, was over 85% in all age groups showing a high exposure of villagers to P. falciparum. OD values in ELISA were positively correlated with age. There was no correlation between the level of IgG against CSP and the multiplicity of P. falciparum infections determined by PCR of msp2. These results imply that in highly endemic areas multiplicity of infection is not directly correlated with exposure to P. falciparum.

Adolescent↗
PubMed2000

Detection of nanocolloids with flow-field flow fractionation and laser-induced breakdown detection.

A new nanosize colloid detection method comprised of flow-field flow fractionation (FFFF) with laser-induced breakdown detection (LIBD) is presented, which is capable of characterizing the colloid size distribution as well as determining the number density of each size fraction in very low concentrations. The method facilitates the detection of aquatic colloids particularly in the lower range of nanometer size (< 50 nm) with the sensitivity much higher than a laser light-scattering method (LLS), i.e., the lower ppb range. The method is tested with a mixture of polystyrene colloids in three different nominal sizes, 19, 50, and 102 nm, and the results are compared with those of the LLS method. For colloids of 19-nm diameter, the present method demonstrates the detection sensitivity over 3 orders of magnitude better than that of the LLS method. The limitation of the detection sensitivity arises from the surface bleeding of a ceramic frit overlying the separation channel of the used FFFF instrument.

Chemical Fractionation↗
PubMed2000

Plasmodium falciparum: cloned and expressed CIDR domains of PfEMP1 bind to chondroitin sulfate A.

Adherence of erythrocytes infected with mature asexual Plasmodium falciparum parasites (iRBC) to microvascular endothelial cells contributes to the pathology of P. falciparum malaria. It has been shown that the variant P. falciparum erythrocyte membrane protein 1 (PfEMP1) confers adhesion to a wide range of cell surface receptors. Previously, the cysteine-rich interdomain region (CIDR) of PfEMP1 has been identified as binding site to CD36. We provide evidence that the same region can also mediate binding to chondroitin sulfate A (CSA). CIDR domains of two different parasite strains were expressed in Escherichia coli as a 6xHis-tagged protein. Purified recombinant protein bound to Chinese hamster ovary (CHO) cells which naturally express chondroitin sulfate A. Treatment of wild-type CHO cells with chondroitinase ABC reduced binding up to 94.4%. Competitive binding using soluble CSA inhibited binding to CHO cells by up to 100% at 2 mg/ml and by 62.4% at 0.5 mg/ml, whereas 1 mg/ml heparan sulfate had only a little effect (18.1%). In contrast, a recombinant 6xHis-tagged DBL1 domain showed no binding to wild-type CHO cells. Such an approach of analyzing various domains of PfEMP1 as recombinant proteins may elucidate their functions and may lead to novel anti-adherence therapeutics, especially for maternal malaria infections.

Amino Acid Sequence↗
PubMed2000

Plasmodium falciparum: expression of gametocyte-specific genes in monolayer cultures and malaria-positive blood samples.

In order to facilitate molecular epidemiological studies on the transmission of the malaria parasite Plasmodium falciparum a sensitive assay for gametocyte detection based on RT-PCR was developed. The transcription of the sexual stage-specific genes Pfs16, Pfs48/45, Pfs230, and Pfs25, as well as the sexual stage- and sporozoite-specific S 18S rRNA, was detected by RT-PCR. S 18S rRNA was present in seven of nine P. falciparum-positive blood samples, despite the lack of microscopic detection of gametocytes and a parasitemia below 0.1%. Expression of the other four gametocyte-specific genes was detected less frequently in malaria-positive blood samples. These findings indicate that RT-PCR of S 18S rRNA is a highly sensitive method for gametocyte detection and, furthermore, that gametocytes are present in the peripheral blood of most malaria carriers, even if the parasitemia is below 0.1%. To determinate the expression pattern of sexual stage-specific genes in more detail, RT-PCR was performed at consecutive time points of highly synchronized monolayer cell cultures. Transcripts of all examined genes except Pfs25 were detected directly after invasion of merozoites of the strain NF54 in red blood cells.

Animals↗
PubMed2000

Molecular approaches to epidemiology and clinical aspects of malaria.

Malaria is a problem of global importance, responsible for 1-2 million deaths per year, mainly in African children, as well as considerable morbidity manifested as severe anaemia and encephalopathy in young children. Fundamental to the development of new tools for malaria control in humans is an increased understanding of key features of malaria infection, such as the diversity of outcome in different individuals, the understanding of different manifestations of the disease and of the mechanisms of immunity that allow clinical protection in the face of ongoing low-grade infection (concomitant immunity or premunition). Here, Graham Brown and colleagues review some of the ways in which molecular approaches might be used to increase our understanding of the epidemiology and clinical manifestations of malaria, as discussed at the Molecular Approaches to Malaria conference (MAM2000), Lorne, Australia, 2-5 February 2000.

Animals↗
PubMed2000

Genetic analysis of IgG subclass responses against RESA and MSP2 of Plasmodium falciparum in adults in Papua New Guinea.

Contributions of environmental and genetic factors to IgG subclass responses against Plasmodium falciparum antigens RESA and MSP2 were investigated among adults in a highly endemic area of Papua New Guinea. Heritabilities were estimated using variance component analysis. Familial aggregation of several responses was found, including IgG1, IgG2 and IgG3 responses against RESA, IgG1 and IgG3 responses against the 3D7 form of MSP2 and IgG1, IgG2 responses against the FC27 form of MSP2. Allowance for sharing of houses explained some of the non-genetic variance but not the familial aggregation. The variance of IgG3 responses against RESA and IgG1, IgG2 against MSP2 (FC27) was partly explained by sharing of HLA class II genotypes, although heritability was low. Segregation analyses indicated that any genetic regulation was more complex than governed by a single major gene. Such host genetic variation in responses to specific malaria antigens has implications for immuno-epidemiology and vaccine development.

Adolescent↗
PubMed2000

Evolution of Pacific/Asian populations inferred from HLA class II allele frequency distributions.

The allele frequency distributions for the HLA class II loci, DRB1, DQB1 and DPB1, in eight Pacific/Asian populations: Hawaiian, Samoan, Malay, Papua New Guinea (PNG) Highlands, and two Indonesian and PNG Lowland groups, were determined using high-resolution polymerase chain reaction/sequence-specific oligonucleotide probe (PCR/SSOP) typing methods. The allele frequency distributions for the HLA-DRB1 locus were determined for a third Indonesian population as well as for an additional Filipino population. DRB1 alleles in the DR2 serogroup (or allelic lineage) are very common in this region; in some populations, more than 50% of the alleles belong to this serogroup. The DRB1*1502 allele is frequent in nine of the ten populations studied, reaching a frequency of 0.48 in one Indonesian population and among Filipinos. Extensive DR-DQ haplotype diversity was detected in these populations. Seven different DR2-DQB1 haplotypes were observed in the Indonesian and PNG Lowland populations, eight in the PNG Highlands and ten in Malays and Filipinos. The DRB1*0410 allele, commonly observed in Australia, is observed in the PNG Highlands at a low frequency (f=0.03) and is absent in the other populations. Two additional DRB1 alleles commonly observed in Australia, DRB1*0405 and *1407, are also observed in the PNG Highlands at high frequencies (f=0.132 and 0.126), while they are rare in the PNG Lowlands (f=0.039 and 0.013). These alleles are generally rare or absent in the other populations. The DPB1*0501 allele, common in Chinese and Japanese populations, is most frequent in the Samoan, Hawaiian, Indonesian, and Malay populations, and the *0401 allele is the most frequent DPB1 allele in the PNG Lowlands. Both of these alleles have the same very high frequency (f=0.34) in the PNG Highlands. Analyses of homozygosity (the Ewens-Watterson F statistic) in these and other populations indicate that, while most allele frequency distributions are consistent with balancing selection, values of F for the Indonesian and Javan populations may reflect positive directional selection. Phylogenetic trees constructed using the allele frequencies at the DRB1 locus of the populations reported here, as well as those for additional Pacific, Asian, and Australian populations, indicate that the PNG Highland population is more closely related to Australian populations than to PNG Lowland populations, while the PNG Lowlands are more closely related to other Melanesian populations.

Alleles↗
PubMed1999

Rapid DNA extraction for molecular epidemiological studies of malaria.

DNA isolation from blood samples collected in molecular epidemiological studies is crucial for the quality and reproducibility of data. Blood samples from two malaria endemic sites have been prepared by four different DNA isolation methods with subsequent PCR amplification of the msp2 locus of Plasmodium falciparum. We tested a rapid boiling method; the guanadine isothiocyanate DNA extraction; QIAmp blood kit; and the ISOCODE STIX PCR template preparation dipstick, and analysed the numbers of concurrent infections/sample. The rapid boiling method and the ISOCODE STIX provided overall the best sensitivity combined with ease of handling. The possibility to store and ship the ISOCODE STIX at ambient temperature adds further advantage to this method.

Animals↗
PubMed1999

Heritability and segregation analysis of immune responses to specific malaria antigens in Papua New Guinea.

Familial patterns of inheritance of immune responses to specific Plasmodium falciparum antigens were studied in 214 adults in an area of Papua New Guinea highly endemic for malaria. Preliminary variance component analysis indicated familial aggregation in both humoral and cellular immune responses against the ring-infected erythrocyte surface antigen (RESA) and the FC27 allele of the Merozoite surface antigen 2 (MSA-2). Including a term for sharing houses in the models affected only the antibody response to RESA. Segregation analysis of the antibody responses against RESA indicated inheritance via a multifactorial model and analysis of the proliferation response suggested a possible recessive major gene. The best fitting models for the immune responses against MSA-2 (FC27) postulated dominant major gene inheritance. We found no significant associations between HLA class I or II alleles and these two antigens in this population. Although there was evidence of familial aggregation of antibody responses to MSA-2 (3D7), the segregation analysis failed to identify a mode of inheritance. There was little or no heritability of either humoral or cellular immune responses against the NANP repeats of the Circumsporozoite protein (NANP), the synthetic malaria vaccine SPf66, or a preparation of MSA-2 (3D7) from which the repetitive part was deleted (MSA-2 (d3D7)). Although it is often difficult to separate genetic effects from the effects of living in the same environment, it appears that some immune responses against certain malaria antigens may be partly influenced by genetic factors.

Adult↗
PubMed1999

Genotypes of merozoite surface protein 2 of Plasmodium falciparum in Tanzania.

The merozoite surface protein 2 (MSP2) of Plasmodium falciparum is extremely polymorphic: 82 different msp2 alleles were found in 4 studies of molecular epidemiology conducted in Tanzania. This diversity renders msp2 suitable as a marker gene for the genotyping of P. falciparum infections. Amplification of msp2 by the polymerase chain reaction (PCR), and subsequent restriction digests of the PCR product (PCR-restriction fragment length polymorphism genotyping), has proved to be an informative tool for enumerating multiple concurrent infections in a blood sample, and distinguishing individual alleles. Depending on the specific questions asked in a genotyping study, analytical techniques of different degrees of complexity are employed. The restriction fragments resulting from a single HinfI digest generally allow the enumeration of multiple concurrent infections and the determination of their allelic families. When a restriction pattern is too complex to be resolved, owing to the high number of concurrent infections, or due to the appearance of previously undescribed alleles, one or more additional digests (DdeI, RsaI, ScrfI) may be necessary. To determine individual alleles unequivocally, in particular in longitudinal studies, when several consecutive samples need to be compared with each other, a more detailed analysis involving all 3 additional digests is applied. The methodological experience and results gained in 4 epidemiological field studies involving msp2 genotyping are summarized. We also provide the HinfI restriction patterns and some nucleotide sequences of the alleles found so far in our studies in Tanzania.

Alleles↗
PubMed1999

Age dependence of the multiplicity of Plasmodium falciparum infections and of other malariological indices in an area of high endemicity.

The relationship between age and various malariological indices in the Kilombero valley of Tanzania were examined by compiling data from 6 different community studies carried out between 1989 and 1996. The rate of acquisition of Plasmodium falciparum infection was highest in children 1-5 years of age, while recovery rates were lowest between the first birthday and early adolescence. As a result, peak prevalence was reached in 3-5 years old children. However, the prevalence of clinical malaria (estimated from the excess risk of axillary temperatures > or = 37.5 degrees C attributable to parasitaemia) was highest in children under one year of age. The peak in multiplicity of infection (identified by polymerase chain reaction-restriction fragment length polymorphism of the msp2 locus) occurred in 3-7 years old children. There was a significant correlation between parasite density and multiplicity of infection in infants and young children (1-2 years of age) but not in older individuals.

Adolescent↗
PubMed1999

Multiple Plasmodium falciparum infections in Tanzanian infants.

Paired blood samples from 99 Tanzanian infants were analysed to examine the infection dynamics of Plasmodium falciparum during the first year of life. Infecting parasites were genotyped by polymerase chain reaction amplification of the polymorphic gene for the merozoite surface protein 2 and subsequent analysis according to the resulting restriction fragment length polymorphism pattern. The same samples served as controls in a parallel case-control study for which an additional blood sample was taken from each child during a fever episode. The relationship of the number of concurrent infections (multiplicity) with age and morbidity was analysed and results were compared to those of a similar study on older children between 2 and 7 years of age, carried out in the same village at the same time. The mean of 2 infecting genotypes per positive blood sample from community surveys was low compared to that in older children, and there was no significant age-dependency of multiplicity within the first year of life. Multiplicity of infection in fever cases was also independent of age. In infants, multiplicity was positively associated with parasite density and risk of clinical malaria, in contrast to the situation in older children (> 2 years). The findings help in the understanding of infection dynamics, premunition, and development of semi-immunity in malaria.

Age Factors↗