Medical Informatics in Medical Research

Objectives: Computers are widely used for data management in clinical trials in the developed coutries, unlike in developing countries. Dependable systems are vital for data management, and medical decision making in clinical research. Monitoring and evaluation of data management is critical.

In this paper we describe database structures and procedures of systems used to implement, coordinate, and sustain data management in Africa. We outline major lessons, challenges and successes achieved, and recommendations to improve medical informatics application in biomedical research in sub-Saharan Africa.

Methods: A consortium of experienced research units at five sites in Africa in studying children with disease formed a new clinical trials network, Severe Malaria in African Children. In December 2000, the network introduced an observational study involving these hospital-based sites. After prototyping, relational database management systems were implemented for data entry and verification, data submission and quality assurance monitoring.

Results: Between 2000 and 2005, 25,858 patients were enrolled. Failure to meet data submission deadline and data entry errors correlated positively (correlation coefficient, r = 0.82), with more errors occurring when data was submitted late. Data submission lateness correlated inversely with hospital admissions (r = –0.62).

Conclusions: Developing and sustaining dependable DBMS, ongoing modifications to optimize data management is crucial for clinical studies. Monitoring and communication systems are vital in multi-center networks for good data management. Data timeliness is associated with data quality and hospital admissions.

Preliminary studies developing methods for the control of Chrysomya putoria, the African latrine fly, in pit latrines in The Gambia

Objective

To explore ways of controlling Chrysomya putoria, the African latrine fly, in pit latrines. As pit latrines are a major source of these flies, eliminating these important breeding sites is likely to reduce village fly populations, and may reduce the spread of diarrhoeal pathogens.

Methods

We treated 24 latrines in a Gambian village: six each with (i) pyriproxyfen, an insect juvenile hormone mimic formulated as Sumilarv® 0.5G, a 0.5% pyriproxyfen granule, (ii) expanded polystyrene beads (EPB), (iii) local soap or (iv) no treatment as controls. Flies were collected using exit traps placed over the drop holes, weekly for five weeks. In a separate study, we tested whether latrines also function as efficient flytraps using the faecal odours as attractants. We constructed six pit latrines each with a built-in flytrap and tested their catching efficiency compared to six fish-baited box traps positioned 10 m from the latrine. Focus group discussions conducted afterwards assessed the acceptability of the flytrap latrines.

Results

Numbers of emerging C. putoria were reduced by 96.0% (95% CIs: 94.5–97.2%) 4–5 weeks after treatment with pyriproxyfen; by 64.2% (95% CIs: 51.8–73.5%) after treatment with local soap; by 41.3% (95% CIs = 24.0–54.7%) after treatment with EPB 3–5 weeks after treatment. Flytraps placed on latrines collected C. putoria and were deemed acceptable to local communities.

Conclusions

Sumilarv 0.5G shows promise as a chemical control agent, whilst odour-baited latrine traps may prove a useful method of non-chemical fly control. Both methods warrant further development to reduce fly production from pit latrines. A combination of interventions may prove effective for the control of latrine flies and the diseases they transmit.

Boosting antibody responses to Plasmodium falciparum merozoite antigens in children with highly seasonal exposure to infection

Longitudinal cohort studies are important to describe the dynamics of naturally acquired antibody response profiles to defined Plasmodium falciparum malaria antigens relative to clinical malaria episodes. In children under 7 years of age in The Gambia, serum IgG responses were measured to P. falciparum merozoite antigens AMA1, EBA175, MSP1(19), MSP2 and crude schizont extract, over a 10-month period. Persistence of antibody responses was measured in 152 children during the dry season when there was virtually no malaria transmission, and 103 children were monitored for new episodes of clinical malaria during the subsequent wet season when transmission occurred. Children who experienced clinical malaria had lower antibody levels at the start of the study than those who remained free from malaria. Associations between dry season antibody persistence and subsequent wet season antibody levels suggested robust immunological memory responses. Mean antibody levels to all antigens were elevated by the end of the wet season in children who experienced clinical malaria; each of these children had a boosted antibody response to at least one antigen. In all children, antibody avidities were lower against MSP2 than other antigens, a difference that did not change throughout the study period or in relation to clinical malaria episodes.

MALVAC 2009: progress and challenges in development of whole organism malaria vaccines for endemic countries, 3-4 June 2009, Dakar, Senegal

Research and development into whole organism malaria vaccines is progressing rapidly thanks to the major investments over recent years from several funders, and the commitment and interest of many leading researchers. Progress includes the discovery of potential new candidate vaccines and the start of the first phase 1/2a clinical trial of the radiation attenuated sporozoite approach for Plasmodium falciparum, under US Food and Drug Administration regulatory oversight. A group of leading scientists, clinical trialists and stakeholders, together with representatives of regulatory authorities including some from African countries, met recently to document the issues that will require detailed consideration to assess this promising approach. Questions related to scale-up, quality, purity and consistency of a manufacturing process using mosquitoes to generate a commercial product, and demonstration of the stability of attenuated sporozoites will need further work. Should a high level of efficacy be demonstrated in clinical challenge studies, it will become a priority to agree in which populations and age groups questions about strain-transcendence and duration of efficacy should be answered, and how clinical development can progress with an approach based on cryopreservation in liquid nitrogen.

Plasmodium falciparum infection of the placenta impacts on the T helper type 1 (Th1)/Th2 balance of neonatal T cells through CD4(+)CD25(+) forkhead box P3(+) regulatory T cells and interleukin-10

Placental malaria infection affects the T helper type 1 (Th1)/Th2 balance in neonatal children. We investigated a potential role of regulatory T cells in this balance by comparing T cell responses of cord blood mononuclear cells (CBMC) from parasitized and non-parasitized placenta of Gambian women. CBMC were depleted of CD4(+)CD25(+) forkhead box P3 (FoxP3)(+) regulatory T cells and analysed in vitro for their ability to produce interferon (IFN)-gamma, sCD30 and interleukin (IL)-10 in response to phytohaemagglutinin (PHA), live Plasmodium falciparum, schizont extracts and the recombinant P. falciparum blood stage antigen merozoite surface protein 1 (MSP1(19)). As expected, lower IFN-gamma and higher sCD30 responses were observed for the cells from the parasitized group. In addition, higher IL-10 levels were produced by CBMC from the parasitized group. Depletion of regulatory T cells decreased IL-10 production, which resulted in a restoration of IFN-gamma expression in response to all stimuli. The Th2 marker sCD30 remained significantly higher in the parasitized group in response to malaria protein antigens while similar levels were recovered between both groups in response to live P. falciparum. Similar effects were observed by adding an antibody that blocks IL-10 function. These results suggest that the impact of P. falciparum infection on Th1 differentiation of neonatal T cells can be ascribed to regulatory T cells through production of IL-10.

Variation in the ICAM1 gene is not associated with severe malaria phenotypes

Evidence from autopsy and in vitro binding studies suggests that adhesion of erythrocytes infected with Plasmodium falciparum to the human host intercellular adhesion molecule (ICAM)-1 receptor is important in the pathogenesis of severe malaria. Previous association studies between polymorphisms in the ICAM1 gene and susceptibility to severe malarial phenotypes have been inconclusive and often contradictory. We performed genetic association studies with 15 single nucleotide polymorphisms (SNPs) around the ICAM1 locus. All SNPs were screened in a family study of 1071 trios from The Gambia, Malawi and Kenya. Two key non-synonymous SNPs with previously reported associations, rs5491 (K56M or 'ICAM-1(Kilifi)') and rs5498 (K469E), were tested in an additional 708 Gambian trios and a case-control study of 4058 individuals. None of the polymorphisms were associated with severe malaria phenotypes. Pooled results across our studies for ICAM-1(Kilifi) were, in severe malaria, odds ratio (OR) 1.02, 95% confidence interval (CI) 0.96-1.09, P=0.54, and cerebral malaria OR 1.07, CI 0.97-1.17, P=0.17. We assess the available epidemiological, population genetic and functional evidence that links ICAM-1(Kilifi) to severe malaria susceptibility.

A hallmark of balancing selection is present at the promoter region of interleukin 10

As an anti-inflammatory mediator IL10 is beneficial in certain contexts and deleterious in others. As increased production of IL10 favours protection against inflammatory disease, whereas low production promotes elimination of foreign pathogens by the host, we investigated the possible influence of balancing selection at this locus. We began by resequencing 48 European and 48 African chromosomes across 2.2 kb of the IL10 promoter region, and compared this with four neighbouring gene regions: MK2, IL19, IL20 and IL24. Analysis of nucleotide diversity showed a positive Tajima's D-test for IL10 in Europeans, of borderline statistical significance (1.89, P=0.05). Analysis of F(st) values showed significant population divergence at MK2, IL19, IL20 and IL24 (P<0.01) but not at IL10. Taken together, these findings are consistent with the hypothesis that balancing selection has played a role in the evolution of polymorphisms in the IL10 promoter region.

Congestive heart failure (CHF) in older women treated with anthracycline (A) chemotherapy (C)

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Background: There are little available data on the long-term cardiac safety of anthracycline chemotherapy in women over age 65, so we evaluated rates and predictors of CHF in this population of older women. Methods: We used data from the Surveillance, Epidemiology, and End Results-Medicare (SEER-Medicare) database and included women aged 66–90 years who were diagnosed with breast cancer from 1992–1999, had no other cancers, and no history of CHF. Multivariable Cox regression analysis was used to estimate the 5- and 10-year cumulative rates of CHF and to determine the factors independently associated with the development of CHF. Results: A total of 34,621 women were included in this observational study: 28,640 who received no C, 3253 who received non-A C, and 2728 who received A C. Women who received A tended to be younger, have lower comorbidity scores, and have more advanced disease than women treated with non-A chemo or women who did not receive chemotherapy (p<0.001 for each). By multivariable Cox regression analysis, the 5- and 10-year rates of CHF in women aged 66–70 years were 19% and 47% for the A C cohort, 14% and 33% for the non-A C cohort, and 12% and 28% for the no C cohort. The adjusted hazard ratio was 1.45 (95% CI 1.19–1.76) for A C versus other C and was 0.97 (95% CI 0.82–1.14) for no C versus other C. The rates of CHF were not statistically different among women in the older age cohorts, although selection biases were likely stronger. Other significant predictors of CHF included black race (HR 1.28, 1.17–1.40), increasing comorbidity, and preceding diagnosis of hypertension (HR 1.40, 1.34–1.47), diabetes (HR 1.23, 1.16–1.30), and peripheral vascular disease (HR 1.26, 1.19–1.34). Conclusions: Although women ages 66–70 treated with A tended to be healthier than women treated with other types of chemotherapy, the rates of CHF among women treated with A were significantly higher. The difference in rates of CHF continued to increase through 10 years of follow-up.

No significant financial relationships to disclose.

Population-specific patterns of linkage disequilibrium in the human 5q31 region

Linkage disequilibrium across the human genome is generally lower in West Africans than Europeans. However in the 5q31 region, which is rich in immune genes, we find significantly more examples of apparent nonrecombination between distant marker pairs in West Africans. Much of this effect is due to SNPs that are absent in Europeans, possibly reflecting recent positive selection in the West African population.

Medical informatics in medical research - the Severe Malaria in African Children (SMAC) Network's experience

OBJECTIVES

Computers are widely used for data management in clinical trials in the developed countries, unlike in developing countries. Dependable systems are vital for data management, and medical decision making in clinical research. Monitoring and evaluation of data management is critical. In this paper we describe database structures and procedures of systems used to implement, coordinate, and sustain data management in Africa. We outline major lessons, challenges and successes achieved, and recommendations to improve medical informatics application in biomedical research in sub-Saharan Africa.

METHODS

A consortium of experienced research units at five sites in Africa in studying children with disease formed a new clinical trials network, Severe Malaria in African Children. In December 2000, the network introduced an observational study involving these hospital-based sites. After prototyping, relational database management systems were implemented for data entry and verification, data submission and quality assurance monitoring.

RESULTS

Between 2000 and 2005, 25,858 patients were enrolled. Failure to meet data submission deadline and data entry errors correlated positively (correlation coefficient, r = 0.82), with more errors occurring when data was submitted late. Data submission lateness correlated inversely with hospital admissions (r = -0.62).

CONCLUSIONS

Developing and sustaining dependable DBMS, ongoing modifications to optimize data management is crucial for clinical studies. Monitoring and communication systems are vital in multi-center networks for good data management. Data timeliness is associated with data quality and hospital admissions.

A comparison of case-control and family-based association methods: the example of sickle-cell and malaria

There has been much debate about the relative merits of population- and family-based strategies for testing genetic association, yet there is little empirical data that directly compare the two approaches. Here we compare case-control and transmission/disequilibrium test (TDT) study designs using a well-established genetic association, the protective effect of the sickle-cell trait against severe malaria. We find that the two methods give similar estimates of the level of protection (case-control odds ratio = 0.10, 95% confidence interval 0.03-0.23; family-based estimate of the odds ratio = 0.11, 95% confidence interval 0.04-0.25) and similar statistical significance of the result (case-control: chi2= 41.26, p= 10(-10), TDT: chi2= 39.06, p= 10(-10)) when 315 TDT cases are compared to 583 controls. We propose a family plus population control study design, which allows both case-control and TDT analysis of the cases. This combination is robust against the respective weaknesses of the case-control and TDT study designs, namely population structure and segregation distortion. The combined study design is especially cost-effective when cases are difficult to ascertain and, when the case-control and TDT results agree, offers greater confidence in the result.

Analysis of IL10 haplotypic associations with severe malaria

We investigated the association between severe malaria and genetic variation of IL10 in Gambian children, as several lines of evidence indicate that IL10 is protective against severe malaria and that IL10 production is genetically determined. We began by identifying five informative SNPs in the Gambian population that were genotyped in a combined case-control and intrafamilial study including 654 cases of severe malaria, 579 sets of parents and 459 ethnically matched controls. No significant associations were identified with individual SNPs. One haplotype of frequency 0.11 was strongly associated with protection against severe malaria in the case-control analysis (odds ratio 0.52, P=0.00002), but the transmission disequilibrium test in families showed no significant effect. These findings raise the question of whether IL10 associations with severe malaria might be confounded by foetal survival rates or other sources of transmission bias.

Investigation of malaria susceptibility determinants in the IFNG/IL26/IL22 genomic region

Interferon-gamma, encoded by IFNG, is a key immunological mediator that is believed to play both a protective and a pathological role in malaria. Here, we investigate the relationship between IFNG variation and susceptibility to malaria. We began by analysing West African and European haplotype structure and patterns of linkage disequilibrium across a 100 kb genomic region encompassing IFNG and its immediate neighbours IL22 and IL26. A large case-control study of severe malaria in a West Africa population identified several weak associations with individual single-nucleotide polymorphisms in the IFNG and IL22 genes, and defined two IL22 haplotypes that are, respectively, associated with resistance and susceptibility. These data provide a starting point for functional and genetic analysis of the IFNG genomic region in malaria and other infectious and inflammatory conditions affecting African populations.

Clinical evaluation of USCOM ultrasonic cardiac output monitor in cardiac surgical patients in intensive care unit

BACKGROUND

The USCOM ultrasonic cardiac output monitor (USCOM Pty Ltd, Coffs Harbour, NSW, Australia) is a non-invasive device that determines cardiac output by continuous-wave Doppler ultrasound. The aim of this study was to evaluate the accuracy of the USCOM device compared with the thermodilution technique in intensive care patients who had just undergone cardiac surgery.

METHODS

We conducted a prospective study in the 18-bed intensive care unit of a 600-bed tertiary referral hospital. Twenty-four mechanically ventilated patients were studied immediately following cardiac surgery. We evaluated the USCOM monitor by comparing its output with paired measurements obtained by the standard thermodilution technique using a pulmonary artery catheter.

RESULTS

Forty paired measurements were obtained in 22 patients. We were unable to obtain an acceptable signal in the remaining two patients. Comparison of the two techniques showed a bias of 0.18 and limits of agreement of -1.43 to 1.78. The agreement may not be as good between techniques at higher cardiac output values.

CONCLUSIONS

The USCOM monitor has a place in intensive care monitoring. It is accurate, rapid, safe, well-tolerated, non-invasive and cost-effective. The learning curve for skill acquisition is very short. However, during the learning phase the USCOM monitor measurements are rather 'operator dependent'. Its suitability for use in high and low cardiac output states requires further validation.

Complex haplotypic structure of the central MHC region flanking TNF in a West African population

TNF polymorphisms have been associated with susceptibility to malaria and other infectious and inflammatory conditions. We investigated a sample of 150 West African chromosomes to determine linkage disequilibrium (LD) between 25 SNP markers located in an 80 kb segment of the MHC Class III region encompassing TNF and eight neighbouring genes. We observed 45 haplotypes, and 22 of them comprise 80% of the sample. The pattern of LD is remarkably patchy, such that many markers show no LD with adjacent markers but high LD with markers that are much further away. We introduce a method of examining the implications of LD data for disease association studies based on sample size considerations: this shows that certain TNF polymorphisms would be likely to yield positive associations if the true disease allele resided in LTA or BAT1. We conclude that detailed marker maps are needed to resolve the causal origin of disease associations observed at the TNF locus.

Haplotypic relationship between SNP and microsatellite markers at the NOS2A locus in two populations

The density of genetic markers required for successful association mapping of complex diseases depends on linkage disequilibrium (LD) between non-functional markers and functional variants. The haplotypic relationship between stable markers and potentially unstable but highly informative markers (e.g. microsatellites) indicates that LD might be maintained over considerable genetic distance in non-African populations, supporting the use of such 'mixed marker haplotypes' in LD-based mapping, and allowing inferences to be drawn about human origins. We investigated sequence variation in the proximal 2.6 kb of the inducible nitric oxide synthase (NOS2A) promoter and the relationship between SNP haplotypes and a pentanucleotide microsatellite (the 'NOS2A(-2.6) microsatellite') in Gambians and UK Caucasians. UK Caucasians exhibited a subset of sequence diversity observed in Gambians, sharing four of 11 SNPs and a similar haplotypic structure. Five SNPs were found in the sequence of interspersed repetitive DNA elements. In both populations, there was dramatic loss of LD between SNP haplotypes and microsatellite alleles across a very short physical distance, suggesting a high intrinsic mutation rate of the NOS2A(-2.6) microsatellite, the SNP haplotypes are relatively ancient, or that this was a region of frequent recombination. Understanding locus- and population-specific LD is essential when designing and interpreting genetic association studies.

Cellular immunity induced by the recombinant Plasmodium falciparum malaria vaccine, RTS,S/AS02, in semi-immune adults in The Gambia

Vaccination of malaria-naive humans with recombinant RTS,S/AS02, which includes the C-terminus of the circumsporozoite protein (CS), has been shown to induce strong T cell responses to both the whole protein antigen and to peptides from CS. Here we show that strong T cell responses were also observed in a semi-immune population in The Gambia, West Africa. In a Phase I study, 20 adult male volunteers, lifelong residents in a malaria-endemic region, were given three doses of RTS,S/AS02 at 0, 1 and 6 months. Responses to RTS,S, hepatitis B surface antigen and peptides from CS were tested using lymphocyte proliferation, interferon (IFN)-gamma production in microcultures, and IFN-gamma ex vivo and cultured ELISPOT, before and after vaccination. Cytotoxic responses were tested only after vaccination and none were detected. Before vaccination, the majority of the volunteers (15/20) had detectable responses in at least one of the tests. After vaccination, responses increased in all assays except cytotoxicity. The increase was most marked for proliferation; all donors responded to RTS,S after the third dose and all except one donor responded to at least one peptide after the second or third dose. There was a lack of close association of peptide responses detected by the different assays, although in microcultures IFN-gamma responses were found only when proliferative responses were high, and responses by cultured ELISPOT and proliferation were found together more frequently after vaccination. We have therefore identified several peptide-specific T cell responses induced by RTS,S/AS02 which provides a mechanism to investigate potentially protective immune responses in the field.

Plasmodium falciparum infection of the placenta affects newborn immune responses

The effects of exposure to placental malaria infection on newborn immunological responses, in particular Th1/Th2 cytokines and antigen-presenting cell (APC) function, were compared between cord blood mononuclear cells (CBMC) from parasitized and non-parasitized placentas of Gambian women. Cells were analysed in vitro for their ability to respond to mitogens [phorbol myristate acetate (PMA)/ionomycin, phytohaemagglutinin (PHA)], a malaria-unrelated test antigen [purified protein derivative of Mycobacterium tuberculin[purified protein derivative (PPD)] and Plasmodium falciparum schizont extracts. Mitogens induced strong proliferation and secretion of high concentrations of both IL-13 and sCD30 in CBMC from both groups. Conversely, significantly lower amounts of IFN-gamma were induced in the parasitized group in response to low doses of PHA. Protein antigens induced very low amounts of all tested cytokines, in particular IFN-gamma. However, a significantly higher release of sCD30 was observed in response to schizont extracts in the parasitized group. Addition of LPS to activate APC to low doses of PHA or schizont extracts increased the IFN-gamma production in both groups but levels remained lower in CBMC from the parasitized group. This result correlates with the lower production of IL-12 found following lipopolysaccharide (LPS) stimulation in this group. Taken together, these data show that placental infection with P. falciparum affects Th1 differentiation and sCD30 priming of neonatal lymphocytes and that the probable mode of action is via APC.

Clinical evaluation of the HemoSonic monitor in cardiac surgical patients in the ICU

The HemoSonic monitor (HemoSonic 100, Arrow International, Reading, PA, U.S.A.) is a minimally invasive device to determine cardiac output by means of M-mode and pulsed Doppler ultrasound. We evaluated the HemoSonic monitor by comparing its output to paired measurements obtained by the standard thermodilution technique in patients who had recently undergone cardiac surgery. Forty-seven paired measurements were carried out in 13 patients. The correlation between the two methods was very good with a correlation coefficient of 0.81. Comparison of the two techniques using the method described by Bland and Altman showed a mean of the differences of -0.23. The limits of agreement were -2.35 to 1.89. There was a reduced correlation between techniques at higher values of cardiac output. We concluded that the HemoSonic monitor has a place in intensive care monitoring, with good correlation with cardiac output measured by the thermodilution technique. It appears to be less suitable for use in patients with a high cardiac output state. The oesophageal probe is moderately difficult for patients to tolerate and is only appropriate for use in sedated patients. The accuracy of the device is somewhat operator-dependent.

Changes in house design reduce exposure to malaria mosquitoes

House design may affect an individual's exposure to malaria parasites, and hence to disease. We conducted a randomized-controlled study using experimental huts in rural Gambia, to determine whether installing a ceiling or closing the eaves could protect people from malaria mosquitoes. Five treatments were tested against a control hut: plywood ceiling; synthetic-netting ceiling; insecticide-treated synthetic-netting ceiling (deltamethrin 12.5 mg/m2); plastic insect-screen ceiling; or the eaves closed with mud. The acceptability of such interventions was investigated by discussions with local communities. House entry by Anopheles gambiae, the principal African malaria vector, was reduced by the presence of a ceiling: plywood (59% reduction), synthetic-netting (79%), insecticide-treated synthetic-netting (78%), plastic insect-screen (80%, P < 0.001 in all cases) and closed eaves (37%, ns). Similar reductions were also seen with Mansonia spp., vectors of lymphatic filariasis and numerous arboviruses. Netting and insect-screen ceilings probably work as decoy traps attracting mosquitoes into the roof space, but not the room. Ceilings are likely to be well accepted and may be of greatest benefit in areas of low to moderate transmission and when used in combination with other malaria control strategies.

CD40L association with protection from severe malaria

CD40 ligand (CD40L), a glycoprotein involved in B cell proliferation, antigen presenting cell activation, and Ig class switching, is important in the immune response to infection. Rare coding mutations in CD40L can lead to life-threatening immunodeficiency but the potential for common variants to alter disease susceptibility remains to be explored. To identify polymorphisms in CD40L, we sequenced 2.3 kb of the 5' flanking region and the first exon of the gene in DNA samples from 36 Gambian females and one chimpanzee. Diversity was lower than the average reported for other areas of the X chromosome, and only two polymorphisms were identified. The polymorphisms were genotyped in DNA samples from 957 Gambian individuals, cases and controls from a study of severe malaria. A significant reduction in risk for severe malaria (OR = 0.52, P = 0.002) was associated with males hemizygous for the CD40L-726C. Analysis by transmission disequilibrium test of 371 cases, for whom DNA from both parents was also available, confirmed the result was not due to stratification (P = 0.04). A similar but non-significant trend was found in females. This preliminary association of a common variant in CD40L with a malaria resistance phenotype encourages further genetic characterization of the role of CD40L in infectious disease.

Pharmacological principles of antibiotic prescription in the critically ill

The goal of antimicrobial prescription is to achieve effective drug concentrations. Standard antimicrobial dosing regimens are based on research performed often decades ago and for the most part with patients who were not critically ill. More recent insights into antibiotic activity (e.g. the importance of high peak/MIC ratios for aminoglycosides and time above MIC for beta-lactam antibiotics), drug pharmacokinetics (e.g. increased volume of distribution and altered clearances) and the pathogenesis of sepsis (e.g. third space losses and altered creatinine clearances) have made re-evaluation of dosing regimens necessary for the critically ill. The inflammatory response associated with sepsis results in a rapid decrease in serum albumin levels, large fluid shifts and third space losses, initially with a high cardiac output. In turn these changes result in increased creatinine clearance and increased renal drug clearance. Unless these effects are offset by ensuing renal and/or hepatic impairment, with subsequent drug accumulation, antibiotic levels may be too low for optimal efficacy. The institution of continuous renal replacement therapy separately affects antibiotic clearances, and therefore dosing, even further. This article reviews relevant literature and offers principles for more effective and appropriate antibiotic dosing in the critically ill, based on the pharmacokinetic and pharmacodynamic principles of the main antibiotic groups (aminoglyosides, glycopeptides, beta-lactams, carbapenems and quinolones) and knowledge of the pathophysiology of the inflammatory response syndrome. Finally it also provides some guidance on the basic principles of drug prescription for patients receiving continuous renal replacement therapy.

Ciprofloxacin pharmacokinetic profiles in paediatric sepsis: how much ciprofloxacin is enough?

OBJECTIVE

To determine the pharmacokinetic profile of ciprofloxacin 20 mg/kg per day (10 mg/kg administered intravenously 12 hourly) in paediatric patients with severe sepsis.

DESIGN

Open and prospective.

SETTING

Tertiary referral multi-disciplinary ICU.

PATIENTS

Twenty patients (two groups - group A: 3 months-1 year; group B 1-5 years).

INTERVENTIONS

Timed blood samples were taken for pharmacokinetics after the first dose (D(0)), as well as day 2 (D(2)) and then between days 6-8.

MEASUREMENTS AND RESULTS

Ciprofloxacin serum levels were measured by high performance liquid chromatography. Demographic and clinical data and all adverse events were noted. Standard pharmacokinetic variables were calculated by non-compartmental methods. Peak concentrations (C(max)) for group A were D(0) 6.1+/-1.2 mg/l, D(2) 9.0+/-1.8 mg/l and D(7) 5.8+/-1.3 mg/l and, for group B, 7.4+/-1.3 mg/l, 7.8+/-1.6 mg/l and 6.4+/-1.3 mg/l, respectively, for the study periods. Concentration 12 h after the start of infusion (C(min)) for all periods were 0.2 mg/l or less. Areas under the curve (AUC, 12 h) were group A: 15.6+/-1.3, 19.2+/-1.63 and 14.1+/-1.4 mg/h per l, and group B: 15.9+/-1.3, 18.0+/-1.7 and 13.2+/-1.26 mg/h per l. One patient presenting with seizures, initially controlled, had another convulsion and a further patient developed seizures whilst on ciprofloxacin. C(max) in these patients were higher than the average C(max). The convulsions of both patients were easily controlled. No other drug-related serious adverse events occurred. No arthropathy was noted. Three patients died of their underlying disease.

CONCLUSIONS

There was no accumulation of drug even after 7 days of administration. Our C(max) and AUC were lower than that achieved in a similar adult pharmacokinetic study. To achieve end points of area under the inhibitory curve (AUIC) of 100-150 mg/h per l, 10 mg/kg ciprofloxacin eight hourly would be required for some resistant ICU organisms.

Short-range attractiveness of pregnant women to Anopheles gambiae mosquitoes

Malaria is a major cause of illness and an indirect cause of mortality in pregnant women. It can also cause stillbirths and low-birthweight babies. We have shown previously that pregnant women attracted twice as many Anopheles gambiae mosquitoes, the principal African malaria vector, as their non-pregnant counterparts over distances of about 15 m. In the current study (in 1998/99) we compared the short-range attractiveness of both pregnant and non-pregnant women sleeping under untreated bednets in Gambian villages. First, we measured the rate of mosquito entry under bednets and, second, we calculated the proportion of mosquitoes biting mothers under each bednet compared to their children. The feeding preference of An. gambiae collected under nets was determined by DNA fingerprinting blood samples from human subjects sleeping under each bednet and comparing these to fingerprints obtained from mosquito bloodmeals. Pregnant women were more attractive to An. gambiae mosquitoes than non-pregnant women under an untreated bednet. The number of mosquitoes entering bednets each night was 1.7-4.5 times higher in the pregnant group (P = 0.02) and pregnant women also received a higher proportion of bites under the bednets than did non-pregnant women (70% vs 52%, P = 0.001). This study clearly demonstrates that pregnant women are more exposed to malaria parasites than other women, which contributes to the greater vulnerability of pregnant women to malaria.

Naturally exposed populations differ in their T1 and T2 responses to the circumsporozoite protein of Plasmodium falciparum

T-cell responses directed against the circumsporozoite protein (CS) of Plasmodium falciparum can mediate protection against malaria. We determined the frequency of T cells reactive to different regions of the CS in the blood of donors naturally exposed to P. falciparum by examining T1 (gamma interferon [IFN-gamma] ELISPOT assay), T2 (interleukin 4 [IL-4] ELISPOT assay), and proliferative T-cell responses. The proliferative responses were weak, which confirmed previous observations. The responses to the CS in the IL-4 and IFN-gamma ELISPOT assays were also weak (<40 responding cells per 10(6) cells), much weaker than the response to the purified protein derivative of Mycobacterium tuberculosis in the same donors. Moreover, a response in one assay could not be used to predict a response in either of the other assays, suggesting that although these assays may measure different responding cells, all of the responses are weakly induced by natural exposure. Interestingly, the two different study populations used had significantly different T1 and T2 biases in their responses in the C terminus of the protein, suggesting that the extent of P. falciparum exposure can affect regulation of the immune system.

Efficacy of RTS,S/AS02 malaria vaccine against Plasmodium falciparum infection in semi-immune adult men in The Gambia: a randomised trial

BACKGROUND

RTS,S/AS02 is a pre-erythrocytic malaria vaccine based on the circumsporozoite surface protein of Plasmodium falciparum fused to HBsAg, incorporating a new adjuvant (AS02). We did a randomised trial of the efficacy of RTS,S/AS02 against natural P. falciparum infection in semi-immune adult men in The Gambia.

METHODS

306 men aged 18-45 years were randomly assigned three doses of either RTS,S/AS02 or rabies vaccine (control). Volunteers were given sulfadoxine/pyrimethamine 2 weeks before dose 3, and kept under surveillance throughout the malaria transmission season. Blood smears were collected once a week and whenever a volunteer developed symptoms compatible with malaria. The primary endpoint was time to first infection with P. falciparum. Analysis was per protocol.

FINDINGS

250 men (131 in the RTS,S/AS02 group and 119 in the control group) received three doses of vaccine and were followed up for 15 weeks. RTS,S/AS02 was safe and well tolerated. P. falciparum infections occurred significantly earlier in the control group than the RTS,S/AS02 group (Wilcoxon's test p=0.018). Vaccine efficacy, adjusted for confounders, was 34% (95% CI 8.0-53, p=0.014). Protection seemed to wane: estimated efficacy during the first 9 weeks of follow-up was 71% (46-85), but decreased to 0% (-52 to 34) in the last 6 weeks. Vaccination induced strong antibody responses to circumsporozoite protein and strong T-cell responses. Protection was not limited to the NF54 parasite genotype from which the vaccine was derived. 158 men received a fourth dose the next year and were followed up for 9 weeks; during this time, vaccine efficacy was 47% (4-71, p=0.037).

INTERPRETATION

RTS,S/AS02 is safe, immunogenic, and is the first pre-erythrocytic vaccine to show significant protection against natural P. falciparum infection.

Effect of passive zooprophylaxis on malaria transmission in The Gambia

The effect of zooprophylaxis on malaria transmission has not been studied on the African continent despite that the World Health Organization has recommended this intervention method since 1982. The effect of passive zooprophylaxis on malaria vector abundance, mosquito feeding preferences, and infectivity was studied in an area of moderate seasonal transmission in The Gambia. A paired cohort of 204 children <7 yr of age was selected and matched in groups for presence or absence of cattle (Bos taurus) within 20 m of their bedroom. Comparisons were made between mosquitoes collected from the bedrooms of the two groups of children. Other ruminants and equines were present in both groups of compounds. Most of the anopheline mosquitoes (98.5%) collected were Anopheles gambiae sensu lato. There was no difference in the geometric mean number of An. gambiae s.l. mosquitoes caught in houses near or far from cattle. The species composition of the An. gambiae complex was similar in both groups. Blood meal analysis of specimens collected in houses without cattle showed a human blood index (HBI) of 82% for An. Arabiensis (Patton), 56% for An. gambiae sensu stricto (Giles), and 36% for Anopheles Melas (Theobald), indicating that each of these sibling species fed readily on animals. The presence of cattle reduced the HBI of An. arabiensis but did not significantly alter the HBI of An. gambiae s.s. or An. melas. There was no significant difference between the groups in the sporozoite rates of An. gambiae s.l. nor in the estimated malaria transmission risk. These findings suggest that passive zooprophylaxis using cattle does not alter the individual exposure to malaria parasites in The Gambia.

Unique T cell effector functions elicited by Plasmodium falciparum epitopes in malaria-exposed Africans tested by three T cell assays

Natural immunity to malaria is characterized by low level CD4 T cell reactivity detected by either lymphoproliferation or IFN-gamma secretion. Here we show a doubling in the detection rate of responders to the carboxyl terminus of circumsporozoite protein (CS) of Plasmodium falciparum by employing three T cell assays simultaneously: rapid IFN-gamma secretion (ex vivo ELISPOT), IFN-gamma secretion after reactivation of memory T cells and expansion in vitro (cultured ELISPOT), and lymphoproliferation. Remarkably, for no individual peptide did a positive response for one T cell effector function correlate with any other. Thus these CS epitopes elicited unique T cell response patterns in malaria-exposed donors. Novel or important epitope responses may therefore be missed if only one T cell assay is employed. A borderline correlation was found between anti-CS Ab levels and proliferative responses, but no correlation was found with ex vivo or cultured IFN-gamma responses. This suggested that the proliferating population, but not the IFN-gamma-secreting cells, contained cells that provide help for Ab production. The data suggest that natural immunity to malaria is a complex function of T cell subgroups with different effector functions and has important implications for future studies of natural T cell immunity.

Nucleotide diversity of the TNF gene region in an African village

The wide variety of disease associations reported at the TNF locus raises the question of how much variation exists within a single population. To address this question, we sequenced the entire TNF gene in 72 chromosomes from healthy residents of a village in The Gambia, West Africa. We found 12 polymorphisms in 4393 nucleotides, of which five have not been previously described, giving an estimated nucleotide diversity (theta) of 5.6 x 10(-4). A significantly higher frequency of polymorphisms was found in the promoter region than in the coding region (8/1256 vs 0/882 nucleotides, P = 0.02). All polymorphisms with the exception of one rare allele were found to be present in Malawi, which is both geographically and genetically distant from The Gambia. Genotyping of 424 Gambian and 121 Malawian adults showed a significant frequency difference between the two populations for eight of the 12 polymorphisms, but the average fixation index across the variable sites was relatively low (F(ST) = 0.007). We conclude that, at the TNF locus, the nucleotide diversity found within a single African village is similar to the global value for human autosomal genes sampled across different continents.

The influence of placental malaria infection and maternal hypergammaglobulinemia on transplacental transfer of antibodies and IgG subclasses in a rural West African population

Two hundred thirteen mother-baby pairs in The Gambia were studied to determine the influence of placental malaria infection and maternal hypergammaglobulinemia on transplacental antibody transfer. Antibody transfer for herpes simplex virus 1 (HSV-1), respiratory syncytial virus (RSV), and varicella-zoster virus (VZV) was significantly reduced by placental malaria infection by 69%, 58%, and 55%, respectively. Maternal hypergammaglobulinemia was associated with a significant reduction in antibody transfer for HSV-1, RSV, VZV, and pneumococcus by 89%, 90%, 91%, and 88%, respectively. In addition, placental malaria infection was associated with a significant reduction in transfer of IgG1, IgG2, and IgG4 (P<.01, P=.01, and P=.03, respectively) but not of IgG3 (P=.59). Maternal hypergammaglobulinemia significantly impaired the transfer of IgG1 and IgG2 (P=.01) but not of IgG3 or IgG4 (P=.62 and P=.59, respectively). Placental malaria infection and maternal hypergammaglobulinemia were associated with reduction in the transplacental transfer of these specific antibodies, IgG1, and IgG2 in this Gambian population.

Do untreated bednets protect against malaria?

Bednets are thought to offer little, if any, protection against malaria, unless treated with insecticide. There is also concern that the use of untreated nets will cause people sleeping without nets to receive more mosquito bites, and thus increase the malaria risk for other community members. Regular retreatment of nets is therefore viewed as critical for malaria control. However, despite good uptake of nets, many control programmes in Africa have reported low re-treatment rates. We investigated whether untreated bednets had any protective benefit (in October and November 1996) in The Gambia where nets, although widely used, are mostly untreated. Cross-sectional prevalence surveys were carried out in 48 villages and the risk of malaria parasitaemia was compared in young children sleeping with or without nets. Use of an untreated bednet in good condition was associated with a significantly lower prevalence of Plasmodium falciparum infection (51% protection [95% CI 34-64%], P < 0.001). This finding was only partly explained by differences in wealth between households, and children in the poorest households benefited most from sleeping under an untreated net (62% protection [14-83%], P = 0.018). There was no evidence that mosquitoes were diverted to feed on children sleeping without nets. These findings suggest that an untreated net, provided it is in relatively good condition, can protect against malaria. Control programmes should target the poorest households as they may have the most to gain from using nets.

Unusual haplotypic structure of IL8, a susceptibility locus for a common respiratory virus

Interleukin-8 (IL8) is believed to play a role in the pathogenesis of bronchiolitis, a common viral disease of infancy, and a recent U.K. family study identified an association between this disease and the IL8-251A allele. In the present study we report data, from a different set of families, which replicate this finding; combined analysis of 194 nuclear families through use of the transmission/disequilibrium test gives P = .001. To explore the underlying genetic cause, we identified nine single-nucleotide polymorphisms (SNPs) in a 7.6-kb segment spanning the IL8 gene and its promoter region and used six of these SNPs to define the haplotypic structure of the IL8 locus. The IL8-251A allele resides on two haplotypes, only one of which is associated with disease, suggesting that this may not be the functional allele. Europeans show an unusual haplotype genealogy that is dominated by two common haplotypes differing at multiple sites, whereas Africans have much greater haplotypic diversity. These marked haplotype-frequency differences give an F(ST) of.25, and, in the European sample, both Tajima's D statistic (D = 2.58, P = .007) and the Hudson/Kreitman/Aguade test (chi(2) = 4.9, P = .03) reject neutral equilibrium, suggesting that selective pressure may have acted on this locus.

The safety of the combination artesunate and pyrimethamine-sulfadoxine given during pregnancy

Malaria during pregnancy is associated with an increased risk of severe anaemia and low-birthweight babies. Effective intermittent therapy with pyrimethamine-sulfadoxine (PSD) decreases parasitaemia and severe anaemia and improves birthweight in areas where Plasmodium falciparum is sensitive to this drug. Increasing resistance to PSD is a concern and alternative antimalarial regimens during pregnancy are needed. Artesunate with PSD is a promising antimalarial combination but few data are available on the safety of artemisinins when taken during pregnancy. Outcome of pregnancy was evaluated for 287 women in The Gambia who were exposed in June 1999 to a single dose of the combination artesunate and PSD during a mass drug administration and 172 women who were not exposed. Women who received placebo (40) and those who did not participate in the mass drug administration (132) comprised the non-exposed group. There was no difference in the proportion of abortions, stillbirths, or infant deaths among those exposed or not exposed to the drugs. The mean weight of 18 infants born to mothers who had received artesunate and PSD during the third trimester was 3.10 kg compared to a mean weight of 2.62 kg of the 10 infants of untreated mothers (adjusted P value = 0.05). We found no evidence of a teratogenic or otherwise harmful effect of gestational exposure to artesunate and PSD. Treatment of a self-selected group of pregnant women with PSD and artesunate during pregnancy was associated with a greater birthweight, which may have resulted from clearance of malaria parasites. However, the influence of confounding factors cannot be excluded.

Influence of placental malaria infection and maternal hypergammaglobulinaemia on materno-foetal transfer of measles and tetanus antibodies in a rural west African population

Placental malaria infection jeopardizes pregnancy outcome, and its influence may also impair the transplacental transfer of some antibodies. Two hundred and thirteen Gambian mother-baby pairs were studied to determine the influence of placental malaria infection and maternal hypergammaglobulinaemia on transplacental transfer of measles and tetanus antibodies in Gambian population. Placental blood and tissue were collected for placental malaria diagnosis. Cord and maternal sera were tested for total IgG concentration by laser nephelometry and for IgG antibody to tetanus toxoid and measles by ELISA. The prevalence of placental malaria infection was 51.1%. Mothers whose placentae were parasitized had a significantly higher mean total serum IgG (22.0 g/L vs 11.3 g/L, p < 0.001) and measles antibody level (4.02 IU/mL vs 1.21 IU/mL, p < 0.01), but not tetanus antibody, than mothers with non-parasitized placentae. Results of multiple regression analysis showed that placental malaria infection and maternal hypergammaglobulinaemia were associated with the reduction of 72% (95% CI 67.84) and 86% (95% CI 76.91) in transplacental transfer of measles antibody respectively but did not influence the transfer of tetanus antibody. It is concluded that the combined influence of placental malaria infection and maternal hypergammaglobulinaemia is significantly associated with the transfer of impaired measles antibody in this population.

Community perceptions of a mass administration of an antimalarial drug combination in The Gambia

To test the hypothesis that widespread treatment with artemisinin derivatives can reduce malaria transmission, a mass drug administration (MDA) campaign was undertaken in an area of The Gambia in 1999. Coverage of 85% of the target population was achieved, but the intervention did not reduce overall malaria transmission. We studied the perceptions, knowledge and attitudes of the community to the MDA campaign. A validated questionnaire was administered to randomly selected MDA participants (n = 90) and MDA refusers (n = 71). Individuals who believed in the importance of the MDA (adjusted OR 58.3%; 95% CI 17.4-195.8) and those who were aware that a high level of participation was needed for the MDA to be successful (adjusted OR 28.1; 95% CI 10.3-75.9) were more likely to participate. Understanding that the purpose of the MDA was to reduce malaria (adjusted OR 13.9; 95% CI 5.5-35.1) and knowledge of the fact that malaria is transmitted by mosquitoes and of the clinical signs of malaria (adjusted OR 3.4; 95% CI 3.1-9.0) were associated with participation. Individuals who discussed the MDA with other villagers (adjusted OR 5.5; 95% CI 2.2-13.5) and those who attended the sensitization meeting (adjusted OR 2.6; 95% CI 1.1-6.0) were also more likely to participate. Women were significantly more likely to participate in the MDA than men (adjusted OR 3.1; 95% CI 1.5-6.2). Individuals who refused to participate were unlikely to plan participation in future MDAs. One of the most difficult challenges in the implementation of a malaria control strategy such as an MDA is to convince villagers to participate and to make them aware that a high level of participation by the community is needed for success. We found that our sensitization meetings could be improved by giving more information on how the MDA works and finding means to generate small group discussions after the meeting.

Artesunate reduces but does not prevent posttreatment transmission of Plasmodium falciparum to Anopheles gambiae

Combination therapy that includes artemisinin derivatives cures most falciparum malaria infections. Lowering transmission by reducing gametocyte infectivity would be an additional benefit. To examine the effect of such therapy on transmission, Gambian children with Plasmodium falciparum malaria were treated with standard regimens of chloroquine or pyrimethamine-sulfadoxine alone or in combination with 1 or 3 doses of artesunate. The infectivity to mosquitoes of gametocytes in peripheral blood was determined 4 or 7 days after treatment. Infection of mosquitoes was observed in all treatment groups and was positively associated with gametocyte density. The probability of transmission was lowest in those who received pyrimethamine-sulfadoxine and 3 doses of artesunate, and it was 8-fold higher in the group that received pyrimethamine-sulfadoxine alone. Artesunate reduced posttreatment infectivity dramatically but did not abolish it completely. The study raises questions about any policy to use pyrimethamine-sulfadoxine alone as the first-line treatment for malaria.

Comparison of deltamethrin tablet formulation with liquid deltamethrin and permethrin for bednet treatment in The Gambia

The study aim was to compare three formulations, tablet deltamethrin, liquid deltamethrin and liquid permethrin, for their impact on vector behaviour and persistence. Product acceptance, perceived side-effects and user's perceptions of effectiveness were also investigated. At the beginning of the 1998 rainy season, 255 nets in a Gambian village were dipped in one of the three insecticides. Chemical residue analysis immediately after dipping showed that the target doses were reached for the liquid insecticides, but tablet deltamethrin deposited significantly less. Insecticide persistence at 5 months, however, was highest for the tablet formulation. Susceptibility tests established that Anophelines in this area were sensitive to both insecticides. All three formulations appeared effective as very few live Anophelines, or other mosquitoes, were caught under the treated nets. This conclusion was supported by the bioassay data with both deltamethrin formulations giving over 90% mortality soon after dipping and at 3 months, and at 5 months 70.8 and 79.6% were obtained for deltametrin liquid and tablet, respectively. Permethrin appeared less effective at all times (72.4, 86.8, 59.0%). There were no serious side-effects reported by the villagers following dipping. All three treatments were perceived as effective by the majority (92%) of users and most (93%) wanted to use the insecticide again. Deltamethrin tablets thus appear as good as permethrin for treating bednets in The Gambia. In addition, a tablet formulation is considerable easier to pack and distribute.

Identification of frequently recognized dimorphic T-cell epitopes in plasmodium falciparum merozoite surface protein-1 in West and East Africans: lack of correlation of immune recognition and allelic prevalence

The merozoite surface protein-1 (MSP1) is the most studied malaria blood-stage vaccine candidate. Lymphokines such as interferon gamma (IFN-gamma) and interleukin 4 (IL-4) may mediate blood-stage specific protection. Here we identify Plasmodiumfalciparum MSP1 T-cell epitopes capable of rapid induction of IFN-gamma and/or IL-4 from peripheral blood mononuclear cells of East and West African donors. Both allelic forms of these novel MSP1 T-cell epitopes were stimulatory. An unusually high numbers of Gambian responders (> 80%) to these epitopes were observed, suggesting that MSPI reactivity may have been underestimated previously in this population. Surprisingly, IFN-gamma responses to allelic T-cell epitopes failed to correlate with differential antigenic exposure in The Gambia compared to Kenya. These results suggest an unexpected level of immunoregulation of IFN-gamma response with variable allelic T-cell reactivity independent of the level of antigenic exposure. Further analysis of the mechanisms determining this response pattern may be required if vaccines are to overcome this allelic reactivity bias in malaria-exposed populations.

Tracheal foreign body following tube change during percutaneous dilational tracheostomy: a cautionary tale

Although studies have shown percutaneous dilational tracheostomy to be a safe and cost-effective alternative to conventional surgical tracheostomy, there are inherent risks and complications. We report an incident occurring during percutaneous dilational tracheostomy using the Portex technique, in which a significant cuff leak occurring on insertion of the tracheostomy tube necessitated an immediate tube change. During this latter procedure, using a fresh Portex kit and guidewire, the guidewire introducer became dislodged from the guidewire assembly and inadvertently impacted in the trachea. Routine bronchoscopy identified the hazard and the foreign body was successfully removed via the bronchoscope with no adverse sequelae.

Linkage disequilibrium between two chromosomally distinct loci associated with increased resistance to chloroquine in Plasmodium falciparum

Chloroquine-resistance in Plasmodium falciparum is associated with polymorphisms in a locus on or near the cg2 gene on chromosome 7, and in the pfmdr1 gene on chromosome 5. In this study we typed P. falciparum DNA from uncomplicated malaria cases in The Gambia in 1990, 1995 and 1996 for size polymorphism in the omega repeat of cg2, for sequence polymorphisms in pfmdr1 at codons 86 and 184, in dhfr at codon 108 and in the msp2 gene. Chloroquine sensitivity tests were conducted in vitro. A significant but incomplete association was found between the presence of the cg2 Dd2-like omega repeat size polymorphism and in vitro resistance, and between the tyr-86 allele of pfmdr1 and in vitro resistance. Furthermore there was strong linkage disequilibrium between the pfmdr1 asn-86 allele and the cg2 not Dd2-like omega repeat allele located on different chromosomes. In contrast, no linkage disequilibrium was found between these alleles and either the dhfr ser-108 allele or the msp2 IC sequence polymorphism. No significant linkage was measured between pfmdr1 asn-86 and phe-184 although these loci are separated only by 296 base pairs. Our results suggest that genetic elements linked to the cg2 and the pfmdr1 genes are important determinants of chloroquine resistance. It can be concluded that the observed linkage disequilibrium is maintained epistatically through selection by chloroquine.

The tyrosine-86 allele of the pfmdr1 gene of Plasmodium falciparum is associated with increased sensitivity to the anti-malarials mefloquine and artemisinin

Although chloroquine-resistance (CQR) in Plasmodium falciparum is increasing and resistance to other blood schizonticidal anti-malarials has been reported, the molecular basis remains unclear. In this study fresh field isolates were obtained from The Gambia, an area of emerging CQR and tested for sensitivity to the anti-malarial drugs mefloquine, halofantrine, artemisinin, dihydroartemisinin, chloroquine and quinine. Sequence polymorphisms in the pfmdr1 gene and size polymorphisms in the cg2 gene were assessed using PCR-based systems. A strong association was observed between the presence of the tyr-86 allele of pfmdr1 and increased sensitivity to mefloquine and halofantrine, as well as the structurally unrelated drugs artemisinin and dihydroartemisinin. A weaker association was found between the presence of tyr-86 and increased resistance to chloroquine and quinine. The cg2 Dd2-like omega repeat size polymorphism was associated with increased resistance to chloroquine and increased sensitivity to mefloquine and halofantrine. An intragenic association was also found between a polymorphism in the polyasparagine linker region of pfmdr1 and the tyr-86 allele, which may be due to genetic hitchhiking, indicative of recent selection by chloroquine. Our data support a hypothesis where the pfmdr1 gene confers a true multidrug resistance phenotype which is lost by mutation.

High-throughput sequence typing of T-cell epitope polymorphisms in Plasmodium falciparum circumsporozoite protein

We report a method for typing polymorphisms at the T-cell epitopes within the Th2R and Th3R regions of the Plasmodium falciparum circumsporozoite protein (CSP). This method combines the use of PCR and sequence specific oligonucleotide probes (PCR-SSOP), and allows the identification of single nucleotide polymorphisms in these epitope regions. PCR-SSOP is a robust and a high-throughput sequence typing technique which has the same specificity and fidelity as direct sequencing. This method has been developed specifically for the assessment of the protective efficacy of RTS,S/SBAS2 vaccine against the 3D7 strain of P. falciparum (RTS,S/SBAS2 vaccine contains a part of the 3D7 CSP protein) in a phase IIb trial in Gambia which has been completed recently. PCR-SSOP could be used to determine the allelic frequencies of other parasite antigens and their geographical distribution.

Efficacy of artesunate plus pyrimethamine-sulphadoxine for uncomplicated malaria in Gambian children: a double-blind, randomised, controlled trial

BACKGROUND

Resistance to cheap effective antimalarial drugs, especially to pyrimethaminesulphadoxine (Fansidar), is likely to have a striking impact on childhood mortality in sub-Sharan Africa. The use of artesunate (artesunic acid) [corrected] in combination with pyrimethamine-sulphadoxine may delay or prevent resistance. We investigated the efficacy, safety, and tolerability of this combined treatment.

METHODS

We did a double-blind, randomised, placebo-controlled trial in The Gambia. 600 children with acute uncomplicated Plasmodium falciparum malaria, aged 6 months to 10 years, at five health centres were randomly assigned pyrimethaminesulphadoxine (25 mg/500 mg) with placebo; pyrimethamine-sulphadoxine plus one dose of artesunate (4mg/kg bodyweight); or pyrimethamine-sulphadoxine plus one dose 4 mg/kg bodyweight artesunate daily for 3 days. Children were visited at home each day after the start of treatment until parasitaemia had cleared.

FINDINGS

The combined treatment was well tolerated. No adverse reactions attributable to treatment were recorded. By day 1, only 178 (47%) of 381 children treated with artesunate were still parasitaemic, compared with 157 (81%) of 195 children in the pyrimethamine-sulphadoxine alone group (relative risk 1.7 [95% CI 1.5-2.0], p<0.001). Treatment-failure rates at day 14 were 3.1% in the pyrimethamine sulphadoxine alone group, and 3.7% in the one-dose artesunate group (risk difference -0.6% [-4.2 to 3.0]) and 1.6% in the three-dose group (1.5 [1.5-4.5], p=0.048). Symptoms resolved faster in children who received artesunate, but there was no additional benefit for three doses of artesunate over one dose. Children given artesunate were less likely to be gametocytaemic after treatment.

INTERPRETATION

The combined treatment was safe, well tolerated, and effective. The addition of artesunate to malaria treatment regimens in Africa results in lower gametocyte rates and may lower transmission rates.

A phase I safety and immunogenicity trial with the candidate malaria vaccine RTS,S/SBAS2 in semi-immune adults in The Gambia

RTS,S is a novel pre-erythrocytic malaria vaccine based on the circumsporozoite surface protein (CSP) of Plasmodium falciparum linked to hepatitis B surface antigen (HBs) and combined with a novel adjuvant system (SBAS2). We have conducted a Phase I trial with three doses of this vaccine given at 0, 1, and 6 months to 20 semi-immune, adult, male volunteers in The Gambia to assess its safety and immunogenicity. Eighteen of the 20 volunteers completed the study. There were no clinically significant local or systemic adverse events following each vaccination. Hematologic and biochemical indices before and two weeks after each vaccination showed no evidence of toxicity. Antibody titers to both CSP and HBs showed a significant increase after vaccination; these were the largest after the third dose. We conclude that the RTS,S/SBAS2 vaccine induces no significant toxicity in this semi-immune population and produces significant increases in antibody titers to CSP.

Inoculum effect leads to overestimation of in vitro resistance for artemisinin derivatives and standard antimalarials: a Gambian field study

Artemisinin (QHS) and its derivatives are new antimalarials which are effective against Plasmodium falciparum parasites resistant to chloroquine (CQ). As these drugs are introduced it is imperative that resistance is monitored. In this paper we demonstrate that the inoculum size used in in vitro testing influences the measured in vitro susceptibility to QHS and its derivative dihydroartemisinin (DHA) and to mefloquine (MEF) and CQ over the range of parasitaemias routinely used in testing with the WHO in vitro microtest. An increase in parasitaemia and/or haematocrit was accompanied by a decrease in the measured sensitivity of 2 laboratory lines. In the context of a field study testing in vitro susceptibility of parasite isolates from patients with uncomplicated malaria in Fajara, The Gambia we demonstrate that failure to control for inoculum size significantly overestimates the level of resistance to QHS and DHA as well as MEF, halofantrine (HAL) and quinine (QUIN). When controlling for the inoculum effect, cross-resistance was observed between QHS, MEF and HAL suggesting the presence of a multidrug resistance-like mechanism. These studies underline the importance of inoculum size in in vitro susceptibility testing.

A randomized safety and tolerability trial of artesunate plus sulfadoxine--pyrimethamine versus sulfadoxine-pyrimethamine alone for the treatment of uncomplicated malaria in Gambian children

Artemisinin derivatives, such as artesunate, have a short half-life and very rapid anti-malarial activity. Theoretically, using such agents in conjunction with well-established anti-malarial drugs such as sulfadoxine-pyrimethamine may reduce the rate of drug resistance. Such a combination has not previously been used in Africa. We have conducted a pilot safety trial of artesunate (4 mg/kg for 3 days) given with a single dose of sulfadoxine-pyrimethamine (25 mg/kg sulfadoxine) compared to sulfadoxine-pyrimethamine alone among 40 Gambian children with uncomplicated malaria. Both regimens were safe and well tolerated and there were no adverse experiences attributed to the combination. The addition of artesunate resulted in a higher proportion of afebrile children and children with a negative blood film on Day 2, and a reduction in the proportion of gametocyte carriers, when compared to sulfadoxine-pyrimethamine alone.

Interleukin 10-mediated immunosuppression by a variant CD4 T cell epitope of Plasmodium falciparum

The immunodominant CD4 T cell epitope region, Th2R, of the circumsporozoite protein of Plasmodium falciparum is highly polymorphic. Such variation might be utilized by the parasite to escape from or interfere with CD4 T cell effector functions. Here, we show that costimulation with naturally occurring altered peptide ligands (APL) can induce a rapid change from IFNgamma production to the immunosuppressive mediator interleukin 10 (IL-10). This mechanism may contribute to the low levels of T cell responses observed to this pathogen in malaria-endemic areas.

Broadly distributed T cell reactivity, with no immunodominant loci, to the pre-erythrocytic antigen thrombospondin-related adhesive protein of Plasmodium falciparum in West Africans

Protective immunity to malaria has been achieved in human volunteers utilizing the pre-erythrocytic Plasmodium falciparum antigen, the circumsporozoite protein (CS). However, T cell reactivity to CS is focused on several highly polymorphic T cell epitope regions, potentially limiting the efficacy of any vaccine to specific malaria strains. Another important pre-erythrocytic malaria antigen, the thrombospondin-related adhesive protein (TRAP), can induce protection in animal models of malaria, but knowledge of human T cell responses is limited to the identification of CD8 T cell epitopes, with no CD4 epitopes identified to date. This comprehensive study assessed reactivity to overlapping peptides spanning almost the whole of P. falciparum TRAP (PfTRAP), as well as peptides selected on the basis of HLA class II-binding motifs. A total of 50 naturally exposed Gambian adults were assessed to define 26 T cell epitopes in PfTRAP capable of inducing rapid IFN-gamma or IL-4 production, as assessed by enzyme-linked immunospot assays. In contrast to the CS protein, this reactivity was broadly distributed along the length of TRAP. Moreover, of the 26 epitopes identified, 10 were found to be conserved in West Africa.