Search PubMed⌕ Search

Biomedical subjects

Richard Carter

Publications and source records attributed to Richard Carter.

At least 19 recordsLinked to original sources
PubMed2006

The phylogeny of rodent malaria parasites: simultaneous analysis across three genomes.

Species of Plasmodium that naturally infect wild rodents but can also be maintained in laboratory mice have long been used as model systems in which to study the biology of malaria parasites. Several of these rodent parasites are now providing useful genomic comparisons to those species that cause malaria in humans. Here we examined the phylogenetic relationships of 19 strains of rodent malaria parasites including four species native to African thicket rats (Plasmodium berghei, Plasmodium chabaudi, Plasmodium vinckei, and Plasmodium yoelii) and one from a porcupine (Plasmodium atheruri) using DNA sequence data collected from seven genes from each of the three parasite genomes. These included the nuclear dihydrofolate reductase gene and a cysteine protease gene, mitochondrial cytochrome b and cytochrome oxidase I genes, and the elongation factor tufA, caseinolytic protease C, and "open reading frame 470" genes from the apicoplast genome, for a combined total of 5049 nucleotides. Using simultaneous analysis, a method of combining each of the gene partitions into a super-matrix, two equally parsimonious trees were recovered. Bayesian analysis of the dataset produced the same topology. The basic species groups were well supported, with the exception of the placement of P. atheruri within the P. vinckei clade. Named subspecies showed a wide array of genetic differentiation, but fell into monophyletic groups.

Animals↗
PubMed2006

Mixed strain infections and strain-specific protective immunity in the rodent malaria parasite Plasmodium chabaudi chabaudi in mice.

Important to malaria vaccine design is the phenomenon of "strain-specific" immunity. Using an accurate and sensitive assay of parasite genotype, real-time quantitative PCR, we have investigated protective immunity against mixed infections of genetically distinct cloned "strains" of the rodent malaria parasite Plasmodium chabaudi chabaudi in mice. Four strains of P. c. chabaudi, AS, AJ, AQ, and CB, were studied. One round of blood infection and drug cure with a single strain resulted in a partial reduction in parasitemia, compared with levels for naïve mice, in challenge infections with mixed inocula of the immunizing (homologous) strain and a heterologous strain. In all cases, the numbers of blood-stage parasites of each genotype were reduced to similar degrees. After a second, homologous round of infection and drug cure followed by challenge with homologous and heterologous strains, the parasitemias were reduced even further. In these circumstances, moreover, the homologous strain was reduced much faster than the heterologous strain in all of the combinations tested. That the immunity induced by a single infection did not show "strain specificity," while the immunity following a second, homologous infection did, suggests that the "strain-specific" component of protective immunity in malaria may be dependent upon immune memory. The results show that strong, protective immunity induced by and effective against malaria parasites from a single parasite species has a significant "strain-specific" component and that this immunity operates differentially against genetically distinct parasites within the same infection.

Animals↗
PubMed2006

Oliver St John Gogarty, MD (1878-1957): quintessential Irish Literary Renaissance figure.

Oliver St John Gogarty (1878-1957) was a quintessential figure of the Irish literary renaissance. He was a successful surgeon, accomplished lyric poet, a man of letters, a senator in the first Irish Free State and a celebrated wit. While pursuing a successful career in ear, nose, and throat (ENT) surgery, Gogarty served a brief, nearly lethal term in politics. He devoted the last several years of his life to a remarkably versatile literary career, the spectrum of his creativity including elegant lyric poetry, autobiographies, biographies, essays, novels and parodies.

Famous Persons↗
PubMed2006

Measuring malaria.

Explore the source record for details and available documents.

Epidemiologic Methods↗
PubMed2006

A randomized, double-blind, placebo-controlled, clinical trial of the impact of malaria prevention on the educational attainment of school children.

A double-blind, placebo-controlled trial of nine months duration was carried out to investigate the impact of malaria and its prevention on the educational attainment of school children in a malaria-endemic area in southern Sri Lanka where both Plasmodium falciparum and P. vivax infections are prevalent. A total of 587 children attending grades 1-5 in four schools and resident in the area were randomly allocated to chloroquine (n = 295) and placebo (n = 292) arms. Language and mathematics scores of end-of-term school examinations for 1998 and 1999 and number of days absent and reasons for absenteeism during seven months pre-intervention and nine months of the intervention were recorded. The results indicate that there were no differences in language (95% confidence interval [CI] = 48.44-53.78 in chloroquine group and 50.43-55.81 in placebo group) and mathematics (95% CI = 49.24-54.38 in chloroquine group and 51.12-56.38 in placebo group) scores between the two groups prior to the intervention. During the intervention, the malaria incidence rate decreased by 55% (95% CI = 49-61%) and school absenteeism due to malaria was reduced by 62.5% (95% CI = 57-68%) in children who received chloroquine compared with the placebo group. Post-intervention, children who received chloroquine scored approximately 26% higher in both language (95% CI = 21-31%) and mathematics (95% CI = 23-33%) than children who received placebo. In a multivariate model, educational attainment was significantly associated with taking chloroquine prophylaxis and absenteeism due to malaria (P < 0.001 for both) but not due to health causes other than malaria or non-health causes. Language scores were associated with number of malaria attacks (P < 0.022). Educational attainment was significantly better among children whose compliance to chloroquine prophylaxis was higher (P < 0.001). The data suggest that malarial attacks have an adverse impact on the educational attainment of the school child and prevention of these attacks significantly improves educational attainment of children living in malaria-endemic areas.

Achievement↗
PubMed2005

Structural models for the protein family characterized by gamete surface protein Pfs230 of Plasmodium falciparum.

Ps230 is the largest representative of a 10-member family of proteins found in all Plasmodium species. The family is defined by partially conserved, cysteine-rich double domains that are approximately 350 aa in length and have one to three predicted disulfide bridges in each half. In Plasmodium falciparum, the most dangerous human malaria, Pf12 is the smallest member of the family, comprising just one double domain. Pfs230, with 7 double domains, and Pfs48/45 and Pfs47, with 1.5 double domains each, are found on the gamete surfaces and are thus potential candidates for a transmission-blocking vaccine. Fold prediction analyses of the double domains in Pfs230 reveal structural resemblance to SAG1 (surface antigen 1), a surface protein with a double beta-sandwich structure from another apicomplexan parasite, Toxoplasma gondii. Template-directed modeling onto SAG1 clearly establishes the structural link between SAG1 and Pfs230 and produces positions for the cysteines that accord with the disulfide-bonding arrangement predicted for the Pfs230 family in earlier work. A highly clustered region of polymorphisms within the second double domain in Pfs230 maps to one side of the sandwich surface. This observation suggests that this region may be functional and reinforces the validity of these molecular models for the core domains of the Pfs230 family of proteins.

Animals↗
PubMed2005

An AFLP-based genetic linkage map of Plasmodium chabaudi chabaudi.

BACKGROUND: Plasmodium chabaudi chabaudi can be considered as a rodent model of human malaria parasites in the genetic analysis of important characters such as drug resistance and immunity. Despite the availability of some genome sequence data, an extensive genetic linkage map is needed for mapping the genes involved in certain traits. METHODS: The inheritance of 672 Amplified Fragment Length Polymorphism (AFLP) markers from two parental clones (AS and AJ) of P. c. chabaudi was determined in 28 independent recombinant progeny clones. These, AFLP markers and 42 previously mapped Restriction Fragment Length Polymorphism (RFLP) markers (used as chromosomal anchors) were organized into linkage groups using Map Manager software. RESULTS: 614 AFLP markers formed linkage groups assigned to 10 of 14 chromosomes, and 12 other linkage groups not assigned to known chromosomes. The genetic length of the genome was estimated to be about 1676 centiMorgans (cM). The mean map unit size was estimated to be 13.7 kb/cM. This was slightly less then previous estimates for the human malaria parasite, Plasmodium falciparum CONCLUSION: The P. c. chabaudi genetic linkage map presented here is the most extensive and highly resolved so far available for this species. It can be used in conjunction with the genome databases of P. c chabaudi, P. falciparum and Plasmodium yoelii to identify genes underlying important phenotypes such as drug resistance and strain-specific immunity.

Alleles↗
PubMed2005

A genetic approach to the de novo identification of targets of strain-specific immunity in malaria parasites.

Vaccine research in malaria has a high priority. However, identification of specific antigens as candidates for vaccines against asexual blood stages of malaria parasites has been based on largely circumstantial evidence. We describe here how genes encoding target antigens of strain-specific immunity in malaria can be directly located in the parasite's genome without prior information concerning their identity, by the method we call linkage group selection. Two genetically distinct clones of the rodent malaria parasite Plasmodium chabaudi chabaudi, each of which induces an immunity in laboratory mice that is more protective against challenge with itself than with the heterologous strain, were genetically crossed, and the uncloned cross progeny selected in mice that had been made partially immune by infection and drug cure with one or the other parental strain. Proportions of parental alleles in the selected and unselected cross progeny were compared by using quantitative genome-wide molecular markers. A small number, including groups of linked markers forming so-called selection valleys, were markedly reduced under strain-specific immune pressure. A very prominent selection valley was found to contain the gene for merozoite surface protein-1, a major candidate antigen for malaria vaccine development, at the locus at which the strongest reduction under strain-specific immune selection was detected. Closely linked to the merozoite surface protein-1 gene was a gene containing the signature motif of the ring-infected erythrocyte surface antigen family. Another affected locus, unlinked to this selection valley, contained a member of the serine repeat antigen gene family.

Animals↗
PubMed2005

Estimating SNP proportions in populations of malaria parasites by sequencing: validation and applications.

We have developed a rapid and simple method for determining accurately the proportions of alleles or individual malaria clones in a mixed infection. The technique uses a nested PCR reaction to amplify, from parasite mixtures, alleles of genes differing by single nucleotide polymorphisms, simultaneously, using common primers to non-polymorphic sequences. The mixed products are sequenced, and the heights of fluorescence peaks associated with different nucleotides at the polymorphic site used to quantitate the proportions of each allele in the mixture. We have confirmed the accuracy and precision of the method using a set of well-validated mixtures of genetically different malaria parasites. This technique can be used in the mapping of genetic loci underlying phenotypic traits and in the evaluation of the effects of different alleles upon the reproductive success (fitness) of parasites.

Animals↗
PubMed2005

Linkage group selection: rapid gene discovery in malaria parasites.

The identification of parasite genes controlling phenotypes such as drug resistance, virulence, immunogenicity, and transmission is vital to malaria research. Classical genetic methods have achieved these goals only rarely and with difficulty. We describe here a novel genetic method, Linkage Group Selection (LGS), which achieves rapid de novo location of genes encoding selectable phenotypes of malaria parasites. A phenotype-specific selection pressure is applied to the uncloned progeny of a genetic cross between two malaria parasites that differ in the relevant phenotype. Selected and unselected progeny are analyzed using genome-wide quantitative genetic markers. Markers of the "sensitive" parent, which are reduced after selection, are sequenced and located in genomic databases. They are expected to be closely linked to gene(s) determining the phenotype under selection. We have validated LGS with the rodent malaria parasite Plasmodium chabaudi chabaudi using a phenotype, pyrimethamine resistance, whose controlling gene, that encoding dihydrofolate reductase (dhfr), is known. We show that molecular markers closely linked to dhfr, and only those linked to this gene, were reduced or removed by pyrimethamine treatment in accordance with the expectations of LGS.

Animals↗
PubMed2004

Host heterogeneity is a determinant of competitive exclusion or coexistence in genetically diverse malaria infections.

During an infection, malaria parasites compete for limited amounts of food and enemy-free space. Competition affects parasite growth rate, transmission and virulence, and is thus important for parasite evolution. Much evolutionary theory assumes that virulent clones outgrow avirulent ones, favouring the evolution of higher virulence. We infected laboratory mice with a mixture of two Plasmodium chabaudi clones: one virulent, the other avirulent. Using real-time quantitative PCR to track the two parasite clones over the course of the infection, we found that the virulent clone overgrew the avirulent clone. However, host genotype had a major effect on the outcome of competition. In a relatively resistant mouse genotype (C57B1/6J), the avirulent clone was suppressed below detectable levels after 10 days, and apparently lost from the infection. By contrast, in more susceptible mice (CBA/Ca), the avirulent clone was initially suppressed, but it persisted, and during the chronic phase of infection it did better than it did in single infections. Thus, the qualitative outcome of competition depended on host genotype. We suggest that these differences may be explained by different immune responses in the two mouse strains. Host genotype and resistance could therefore play a key role in the outcome of within-host competition between parasite clones and in the evolution of parasite virulence.

Analysis of Variance↗
PubMed2004

Amplified fragment length polymorphism measures proportions of malaria parasites carrying specific alleles in complex genetic mixtures.

We are interested in developing a method for the identification of those genes in malaria parasites which underlie a variety of selectable phenotypes of the parasites including drug resistance and strain-specific immunity. A key aspect of our approach is to subject a genetically mixed population of malaria parasites to a specific phenotypic selection pressure such as the administration of an antimalarial drug and then identify genetic markers affected by the selection. Our aim, therefore, is to be able to identify those genetic markers carried by sensitive parasites which disappear from the population after selection as they should be closely linked to the locus determining the phenotype involved. We have previously identified more than 800 amplified fragment length polymorphisms (AFLP) distinguishing two cloned strains of the rodent malaria parasite Plasmodium chabaudi chabaudi and distributed across the whole of the parasites' genome. Here we evaluate the possibility that the intensities of these AFLP bands are quantitatively related to the proportions of parasite DNA which bear these markers in mixtures of genetically different parasites. We prepared mixtures of DNA and parasitised blood from different mixtures of two genetically distinct clones (AS and AJ) of P. c. chabaudi and analysed AFLP markers amplified from them. The results show that the relative band intensities of AFLP markers are, indeed, linearly related to the proportions of parasite DNA in a genetically mixed sample. The precision of the method is sufficient to detect reliably the effects of phenotypic selection at loci closely linked to a genetic locus under selection.

Alleles↗
PubMed2004

Gene synteny and chloroquine resistance in Plasmodium chabaudi.

Chloroquine resistance in the rodent malaria parasite Plasmodium chabaudi has been shown to be caused by a gene on chromosome 11, and is not linked to orthologues of the Plasmodium falciparum chloroquine resistance transporter (pfcrt) or Pgh-1 (pfmdr1) genes. In the current work, the progeny of crosses between chloroquine-resistant and sensitive clones of P. chabaudi have been analysed for the inheritance of 658 AFLP markers. Markers linked to the chloroquine responses of the progeny, including two which are completely linked, have been genetically mapped, sequenced and their homologues, or closely linked loci, identified in P. falciparum. The chromosome 11 markers most closely linked to chloroquine resistance in P. chabaudi map to loci which are also closely linked in P. falciparum, although in two linkage groups on chromosomes 6 and 13 of this species. The P. falciparum orthologue of the gene conferring chloroquine resistance in P. chabaudi is predicted to lie within a 250 kb region of P. falciparum chromosome 6, containing approximately 50 genes. The genetic order of the markers in P. chabaudi is co-linear with the physical linkage represented in the P. falciparum genome database. The findings provide evidence for extensive conservation of synteny between the two species.

Animals↗
PubMed2004

Influence of intracellular Ca2+ release modulating drugs on bupivacaine infiltration anesthesia in mice.

The endoplasmic reticulum inside neurons can provide enormous amounts of releasable Ca2+ to increase cytosolic Ca2+ levels through the activation of endoplasmic membrane ion channels. Ryanodine (RyR) channels release Ca2+ into the cytosol when activated by Ca2+ influx through voltage-gated channels, or by cyclicADP ribose. Inositol tris-phosphate (IP3) channels are stimulated by phospolipid metabolism and the release of IP3. The hypothesis was tested that drugs that bind RyR or IP3 channels would affect the anesthetic potency of bupivacaine. The radiant heat tail-flick test was used to assess for anesthesia following subcutaneous infiltration of bupivacaine and Ca2+ modulating drugs in the tails of mice. No musculature is contained in the tail that could result in motor block. The RyR channel agonists 4-chloro-m-cresol and poly-L-lysine significantly reduced the anesthetic potency of bupivacaine. The plant alkaloid ryanodine elicited a bi-phasic effect, with low concentrations blocking bupivacaine anesthesia, and a high concentration enhancing anesthesia. Alternatively, the RyR channel antagonist dantrolene sodium dose-dependently increased bupivacaine's potency. However, the IP3 channel drugs were inactive. The IP3 agonist adenophostin A failed to affect bupivacaine anesthesia. Furthermore, bupivacaine was unaffected by the IP3 channel antagonists xestospongin C or low molecular weight heparin. Our results indicate that only the RyR channel drugs modulated the anesthetic effects of bupivacaine. Electrophysiological and molecular studies of sensory dorsal root ganglia neurons, the source of Adelta and C-fiber nociceptors, have demonstrated the presence of RyR3 Ca2+ release channels. This provides the first evidence that RyR channels might affect bupivacaine anesthesia in some fashion.

Anesthesia, Local↗
PubMed2004

Water quality deterioration: a study of household drinking water quality in rural Honduras.

There is growing awareness that drinking-water can become contaminated following its collection from communal sources such as wells and tap-stands, as well as during its storage in the home. This study evaluated the post-supply drinking-water quality in three rural Honduran communities using either a protected hand-dug well or borehole supply. Water management practices were documented as a basis for further research to improve household drinking-water quality. Membrane filtration was used to compare thermotolerant coliform levels in samples taken from community wells and household drinking-water storage containers. Over a 2-year period, water quality was examined in 43 households and detailed observation made of typical collection, storage and usage practice. Substantial water quality deterioration occurred between the points of supply and consumption. Deterioration occurred regularly and frequently, and was experienced by the majority of study households. Only source water quality appeared to be a significant factor in determining household water quality. None of the storage factors examined, i.e. covering the container, type of container, the material from which the container was made, and hours stored, made any significant difference to the stored water quality. Observation of household water management shows that there are multiple points during the collection to use sequence where pollution could occur. The commonality of water management practice would be an asset in introducing appropriate intervention measures.

Data Collection↗