Medical Biology - Research Publications
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ItemNo Preview AvailableCorrection: Does Malaria Affect Placental Development? Evidence from In Vitro Models(Public Library of Science (PLoS), 2013)
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ItemPatterns of protective associations differ for antibodies to &ITP&IT. &ITfalciparum&IT-infected erythrocytes and merozoites in immunity against malaria in children(WILEY, 2017-12)Acquired antibodies play an important role in immunity to P. falciparum malaria and are typically directed towards surface antigens expressed by merozoites and infected erythrocytes (IEs). The importance of specific IE surface antigens as immune targets remains unclear. We evaluated antibodies and protective associations in two cohorts of children in Papua New Guinea. We used genetically-modified P. falciparum to evaluate the importance of PfEMP1 and a P. falciparum isolate with a virulent phenotype. Our findings suggested that PfEMP1 was the dominant target of antibodies to the IE surface, including functional antibodies that promoted opsonic phagocytosis by monocytes. Antibodies were associated with increasing age and concurrent parasitemia, and were higher among children exposed to a higher force-of-infection as determined using molecular detection. Antibodies to IE surface antigens were consistently associated with reduced risk of malaria in both younger and older children. However, protective associations for antibodies to merozoite surface antigens were only observed in older children. This suggests that antibodies to IE surface antigens, particularly PfEMP1, play an earlier role in acquired immunity to malaria, whereas greater exposure is required for protective antibodies to merozoite antigens. These findings have implications for vaccine design and serosurveillance of malaria transmission and immunity.
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ItemPoint-of-care testing and treatment of sexually transmitted infections to improve birth outcomes in high-burden, low-income settings: Study protocol for a cluster randomized crossover trial (the WANTAIM Trial, Papua New Guinea).(F1000 Research Ltd, 2019)Background: Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and bacterial vaginosis have been associated with preterm birth and low birth weight, and are highly prevalent among pregnant women in many low- and middle-income settings. There is conflicting evidence on the potential benefits of screening and treating these infections in pregnancy. Newly available diagnostic technologies make it possible, for the first time, to conduct definitive field trials to fill this knowledge gap. The primary aim of this study is to evaluate whether antenatal point-of-care testing and immediate treatment of these curable sexually transmitted and genital infections (STIs) leads to reduction in preterm birth and low birth weight. Methods: The Women and Newborn Trial of Antenatal Interventions and Management (WANTAIM) is a cluster-randomised crossover trial in Papua New Guinea to compare point-of-care STI testing and immediate treatment with standard antenatal care (which includes the WHO-endorsed STI 'syndromic' management strategy based on clinical features alone without laboratory confirmation). The unit of randomisation is a primary health care facility and its catchment communities. The primary outcome is a composite measure of two events: the proportion of women and their newborns in each trial arm, who experience either preterm birth (delivery <37 completed weeks of gestation as determined by ultrasound) and/or low birth weight (<2500 g measured within 72 hours of birth). The trial will also evaluate neonatal outcomes, as well as the cost-effectiveness, acceptability and health system requirements of this strategy, compared with standard care. Conclusions: WANTAIM is the first randomised trial to evaluate the effectiveness, cost-effectiveness, acceptability and health system requirements of point-of-care STI testing and treatment to improve birth outcomes in high-burden settings. If the intervention is proven to have an impact, the trial will hasten access to these technologies and could improve maternal and neonatal health in high-burden settings worldwide. Registration: ISRCTN37134032.
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ItemPoint-of-care testing and treatment of sexually transmitted infections to improve birth outcomes in high-burden, low-income settings: Study protocol for a cluster randomized crossover trial (the WANTAIM Trial, Papua New Guinea)(F1000 Research Ltd, 2019-03-22)Background: Chlamydia trachomatis , Neisseria gonorrhoeae , Trichomonas vaginalis and bacterial vaginosis have been associated with preterm birth and low birth weight, and are highly prevalent among pregnant women in many low- and middle-income settings. There is conflicting evidence on the potential benefits of screening and treating these infections in pregnancy. Newly available diagnostic technologies make it possible, for the first time, to conduct definitive field trials to fill this knowledge gap. The primary aim of this study is to evaluate whether antenatal point-of-care testing and immediate treatment of these curable sexually transmitted and genital infections (STIs) leads to reduction in preterm birth and low birth weight. Methods : The Women and Newborn Trial of Antenatal Interventions and Management (WANTAIM) is a cluster-randomised crossover trial in Papua New Guinea to compare point-of-care STI testing and immediate treatment with standard antenatal care (which includes the WHO-endorsed STI ‘syndromic’ management strategy based on clinical features alone without laboratory confirmation). The unit of randomisation is a primary health care facility and its catchment communities. The primary outcome is a composite measure of two events: the proportion of women and their newborns in each trial arm, who experience either preterm birth (delivery <37 completed weeks of gestation as determined by ultrasound) and/or low birth weight (<2500 g measured within 72 hours of birth). The trial will also evaluate neonatal outcomes, as well as the cost-effectiveness, acceptability and health system requirements of this strategy, compared with standard care. Conclusions: WANTAIM is the first randomised trial to evaluate the effectiveness, cost-effectiveness, acceptability and health system requirements of point-of-care STI testing and treatment to improve birth outcomes in high-burden settings. If the intervention is proven to have an impact, the trial will hasten access to these technologies and could improve maternal and neonatal health in high-burden settings worldwide. Registration: ISRCTN37134032 .
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ItemA Randomized Open-Label Evaluation of the Antimalarial Prophylactic Efficacy of Azithromycin-Piperaquine versus Sulfadoxine-Pyrimethamine in Pregnant Papua New Guinean Women(American Society for Microbiology, 2019-10-01)Emerging malaria parasite sulfadoxine-pyrimethamine (SP) resistance has prompted assessment of alternatives for intermittent preventive treatment in pregnancy (IPTp). The objective was to evaluate the tolerability and prophylactic efficacy of azithromycin (AZ) plus piperaquine (PQ) in pregnant women in Papua New Guinea. The study was an open-label, randomized, parallel-group trial. A total of 122 women (median gestation, 26 weeks [range, 14 to 32 weeks]) were randomized 1:1 to three daily doses of 1 g AZ plus 960 mg PQ tetraphosphate or single-dose SP (4,500 mg sulfadoxine plus 225 mg pyrimethamine), based on computer-generated block randomization. Tolerability was assessed to day 7, and efficacy was assessed to day 42 (when participants were returned to usual care) and at delivery. Data for 119 participants (AZ-PQ, n = 61; SP, n = 58) were analyzed. Both regimens were well tolerated, but AZ-PQ was associated with more gastrointestinal side effects (31%) and dizziness (21%). Eight women (6.7%) were parasitemic at recruitment but all were aparasitemic by 72 h. There were no differences in blood smear positivity rates between AZ-PQ and SP up to day 42 (0% versus 5.2%; relative risk [RR], 0.14 [95% confidence interval [CI], 0.01 to 2.58] [P = 0.18]; absolute risk reduction [ARR], 5.2% [95% CI, -1.3 to 11.6%]) and at the time of delivery (0% versus 8.7%; RR, 0.11 [95% CI, 0.01 to 2.01] [P = 0.14]; ARR, 8.7% [95% CI, -0.2 to 17.6%]). Of 92 women who were monitored to parturition, 89 (97%) delivered healthy babies; there were 3 stillbirths (SP, n = 1; AZ-PQ, n = 2 [twins]). There was a higher live birth weight (mean ± standard deviation) in the AZ-PQ group (3.13 ± 0.42 versus 2.88 ± 0.55 kg [P = 0.016]; mean difference, 0.25 kg [95% CI, 0.02 to 0.48 kg]). AZ-PQ is a promising candidate for IPTp.
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ItemMonitoringPlasmodium falciparumandPlasmodium vivaxusing microsatellite markers indicates limited changes in population structure after substantial transmission decline in Papua New Guinea(WILEY, 2020-12)Monitoring the genetic structure of pathogen populations may be an economical and sensitive approach to quantify the impact of control on transmission dynamics, highlighting the need for a better understanding of changes in population genetic parameters as transmission declines. Here we describe the first population genetic analysis of two major human malaria parasites, Plasmodium falciparum (Pf) and Plasmodium vivax (Pv), following nationwide distribution of long-lasting insecticide-treated nets (LLINs) in Papua New Guinea (PNG). Parasite isolates from pre- (2005-2006) and post-LLIN (2010-2014) were genotyped using microsatellite markers. Despite parasite prevalence declining substantially (East Sepik Province: Pf = 54.9%-8.5%, Pv = 35.7%-5.6%, Madang Province: Pf = 38.0%-9.0%, Pv: 31.8%-19.7%), genetically diverse and intermixing parasite populations remained. Pf diversity declined modestly post-LLIN relative to pre-LLIN (East Sepik: Rs = 7.1-6.4, HE = 0.77-0.71; Madang: Rs = 8.2-6.1, HE = 0.79-0.71). Unexpectedly, population structure present in pre-LLIN populations was lost post-LLIN, suggesting that more frequent human movement between provinces may have contributed to higher gene flow. Pv prevalence initially declined but increased again in one province, yet diversity remained high throughout the study period (East Sepik: Rs = 11.4-9.3, HE = 0.83-0.80; Madang: Rs = 12.2-14.5, HE = 0.85-0.88). Although genetic differentiation values increased between provinces over time, no significant population structure was observed at any time point. For both species, a decline in multiple infections and increasing clonal transmission and significant multilocus linkage disequilibrium post-LLIN were positive indicators of impact on the parasite population using microsatellite markers. These parameters may be useful adjuncts to traditional epidemiological tools in the early stages of transmission reduction.
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ItemA comparison of non-magnetic and magnetic beads for measuring IgG antibodies against Plasmodium vivax antigens in a multiplexed bead-based assay using Luminex technology (Bio-Plex 200 or MAGPIX)(PUBLIC LIBRARY SCIENCE, 2020-12-04)Multiplexed bead-based assays that use Luminex® xMAP® technology have become popular for measuring antibodies against proteins of interest in many fields, including malaria and more recently SARS-CoV-2/COVID-19. There are currently two formats that are widely used: non-magnetic beads or magnetic beads. Data are lacking regarding the comparability of results obtained using these two types of beads, and for assays run on different instruments. Whilst non-magnetic beads can only be run on flow-based instruments (such as the Luminex® 100/200™ or Bio-Plex® 200), magnetic beads can be run on both these and the newer MAGPIX® instruments. In this study we utilized a panel of purified recombinant Plasmodium vivax proteins and samples from malaria-endemic areas to measure P. vivax-specific IgG responses using different combinations of beads and instruments. We directly compared: i) non-magnetic versus magnetic beads run on a Bio-Plex® 200, ii) magnetic beads run on the Bio-Plex® 200 versus MAGPIX® and iii) non-magnetic beads run on a Bio-Plex® 200 versus magnetic beads run on the MAGPIX®. We also performed an external comparison of our optimized assay. We observed that IgG antibody responses, measured against our panel of P. vivax proteins, were moderately-strongly correlated in all three of our comparisons (pearson r>0.5 for 18/19 proteins), however higher amounts of protein were required for coupling to magnetic beads. Our external comparison indicated that results generated in different laboratories using the same coupled beads are also highly comparable (pearson r>0.7), particularly if a reference standard curve is used.
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ItemCombining different diagnostic studies of lymphatic filariasis for risk mapping in Papua New Guinea: a predictive model from microfilaraemia and antigenaemia prevalence surveys(BMC, 2018-12-04)BACKGROUND: The Global Programme to Eliminate Lymphatic Filariasis has encouraged countries to follow a set of guidelines to help them assess the need for mass drug administration and evaluate its progress. Papua New Guinea (PNG) is one of the highest priority countries in the Western Pacific for lymphatic filariasis and the site of extensive research on lymphatic filariasis and surveys of its prevalence. However, different diagnostic tests have been used and thresholds for each test are unclear. METHODS: We reviewed the prevalence of lymphatic filariasis reported in 295 surveys conducted in PNG between 1990 and 2014, of which 65 used more than one test. Results from different diagnostics were standardised using a set of criteria that included a model to predict antigen prevalence from microfilariae prevalence. We mapped the point location of each of these surveys and categorised their standardised prevalence estimates. RESULTS: Several predictive models were produced and investigated, including the effect of any mass drug administration and number of rounds prior to the surveys. One model was chosen based on goodness of fit parameters and used to predict antigen prevalence for surveys that tested only for microfilariae. Standardised prevalence values show that 72% of all surveys reported a prevalence above 0.05. High prevalence was situated on the coastal north, south and island regions, while the central highland area of Papua New Guinea shows low levels of prevalence. CONCLUSIONS: Our study is the first to provide an explicit predictive relationship between the prevalence values based on empirical results from antigen and microfilaria tests, taking into account the occurrence of mass drug administration. This is a crucial step to combine studies to develop risk maps of lymphatic filariasis for programme planning and evaluation, as shown in the case of Papua New Guinea.
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ItemEfficacy of artemether-lumefantrine and dihydroartemisinin-piperaquine for the treatment of uncomplicated malaria in Papua New Guinea(BMC, 2018-10-05)BACKGROUND: In 2009, the Papua New Guinea (PNG) Department of Health adopted artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DHA-PPQ) as the first- and second-line treatments for uncomplicated malaria, respectively. This study was conducted to assess the efficacy of both drugs following adoption of the new policy. METHODS: Between June 2012 and September 2014, a therapeutic efficacy study was conducted in East Sepik and Milne Bay Provinces of PNG in accordance with the standard World Health Organization (WHO) protocol for surveillance of anti-malarial drug efficacy. Patients ≥ 6 months of age with microscopy confirmed Plasmodium falciparum or Plasmodium vivax mono-infections were enrolled, treated with AL or DHA-PPQ, and followed up for 42 days. Study endpoints were adequate clinical and parasitological response (ACPR) on days 28 and 42. The in vitro efficacy of anti-malarials and the prevalence of selected molecular markers of resistance were also determined. RESULTS: A total of 274 P. falciparum and 70 P. vivax cases were enrolled. The day-42 PCR-corrected ACPR for P. falciparum was 98.1% (104/106) for AL and 100% (135/135) for DHA-PPQ. The day-42 PCR-corrected ACPR for P. vivax was 79.0% (15/19) for AL and 92.3% (36/39) for DHA-PPQ. Day 3 parasite clearance of P. falciparum was 99.2% with AL and 100% with DHA-PPQ. In vitro testing of 96 samples revealed low susceptibility to chloroquine (34% of samples above IC50 threshold) but not to lumefantrine (0%). Molecular markers assessed in a sub-set of the study population indicated high rates of chloroquine resistance in P. falciparum (pfcrt SVMNT: 94.2%, n = 104) and in P. vivax (pvmdr1 Y976F: 64.8%, n = 54). CONCLUSIONS: AL and DHA-PPQ were efficacious as first- and second-line treatments for uncomplicated malaria in PNG. Continued in vivo efficacy monitoring is warranted considering the threat of resistance to artemisinin and partner drugs in the region and scale-up of artemisinin-based combination therapy in PNG.
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ItemMathematical modelling of the impact of expanding levels of malaria control interventions on Plasmodium vivax(NATURE PUBLISHING GROUP, 2018-08-17)Plasmodium vivax poses unique challenges for malaria control and elimination, notably the potential for relapses to maintain transmission in the face of drug-based treatment and vector control strategies. We developed an individual-based mathematical model of P. vivax transmission calibrated to epidemiological data from Papua New Guinea (PNG). In many settings in PNG, increasing bed net coverage is predicted to reduce transmission to less than 0.1% prevalence by light microscopy, however there is substantial risk of rebounds in transmission if interventions are removed prematurely. In several high transmission settings, model simulations predict that combinations of existing interventions are not sufficient to interrupt P. vivax transmission. This analysis highlights the potential options for the future of P. vivax control: maintaining existing public health gains by keeping transmission suppressed through indefinite distribution of interventions; or continued development of strategies based on existing and new interventions to push for further reduction and towards elimination.