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Find video protocols related to scientific articles indexed in Pubmed.
Evaluation of the Efficacy of ChAd63-MVA Vectored Vaccines Expressing CS & ME-TRAP Against Controlled Human Malaria Infection in Malaria Naïve Individuals.
J. Infect. Dis.
PUBLISHED: 10-23-2014
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?Circumsporozoite protein (CS) is the antigenic target for RTS,S, the most advanced malaria vaccine to date. Heterologous prime-boost with the viral vectors ChAd63-MVA is the most potent inducer of T-cells in humans, demonstrating significant efficacy when expressing the pre-erythrocytic antigen insert ME-TRAP. We hypothesised that ChAd63-MVA containing CS may result in significant, clinical protective efficacy. Methods.?We conducted an open-label, two-site partially randomized sporozoite controlled human malaria infection (CHMI) study to compare the clinical efficacy of ChAd63-MVA CS with ChAd63-MVA ME-TRAP. The study was registered at: www.clinicaltrials.gov (NCT01623557).
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Radiological features do not predict failure of two-stage arthroplasty for prosthetic joint infection: a retrospective case-control study.
BMC Musculoskelet Disord
PUBLISHED: 08-27-2014
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The management of prosthetic joint infection is complex and there is a lack of standardisation of approaches. We evaluated the role of plain film radiography in predicting prosthesis failure after the first stage of a two-stage revision procedure in a retrospective case-control study.
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A micro-epidemiological analysis of febrile malaria in Coastal Kenya showing hotspots within hotspots.
Elife
PUBLISHED: 05-21-2014
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Malaria transmission is spatially heterogeneous. This reduces the efficacy of control strategies, but focusing control strategies on clusters or 'hotspots' of transmission may be highly effective. Among 1500 homesteads in coastal Kenya we calculated (a) the fraction of febrile children with positive malaria smears per homestead, and (b) the mean age of children with malaria per homestead. These two measures were inversely correlated, indicating that children in homesteads at higher transmission acquire immunity more rapidly. This inverse correlation increased gradually with increasing spatial scale of analysis, and hotspots of febrile malaria were identified at every scale. We found hotspots within hotspots, down to the level of an individual homestead. Febrile malaria hotspots were temporally unstable, but 4 km radius hotspots could be targeted for 1 month following 1 month periods of surveillance.DOI: http://dx.doi.org/10.7554/eLife.02130.001.
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Translating the Immunogenicity of Prime-boost Immunization With ChAd63 and MVA ME-TRAP From Malaria Naive to Malaria-endemic Populations.
Mol. Ther.
PUBLISHED: 04-26-2014
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To induce a deployable level of efficacy, a successful malaria vaccine would likely benefit from both potent cellular and humoral immunity. These requirements are met by a heterologous prime-boost immunization strategy employing a chimpanzee adenovirus vector followed by modified vaccinia Ankara (MVA), both encoding the pre-erythrocytic malaria antigen ME-thrombospondin-related adhesive protein (TRAP), with high immunogenicity and significant efficacy in UK adults. We undertook two phase 1b open-label studies in adults in Kenya and The Gambia in areas of similar seasonal malaria transmission dynamics and have previously reported safety and basic immunogenicity data. We now report flow cytometry and additional interferon (IFN)-? enzyme-linked immunospot (ELISPOT) data characterizing pre-existing and induced cellular immunity as well as anti-TRAP IgG responses. T-cell responses induced by vaccination averaged 1,254 spot-forming cells (SFC) per million peripheral blood mononuclear cells (PBMC) across both trials and flow cytometry revealed cytokine production from both CD4(+) and CD8(+) T cells with the frequency of CD8(+) IFN-?-secreting monofunctional T cells (previously shown to associate with vaccine efficacy) particularly high in Kenyan adults. Immunization with ChAd63 and MVA ME-TRAP induced strong cellular and humoral immune responses in adults living in two malaria-endemic regions of Africa. This prime-boost approach targeting the pre-erythrocytic stage of the malaria life-cycle is now being assessed for efficacy in a target population.
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A combined analysis of immunogenicity, antibody kinetics and vaccine efficacy from phase 2 trials of the RTS,S malaria vaccine.
BMC Med
PUBLISHED: 03-14-2014
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The RTS,S malaria vaccine is currently undergoing phase 3 trials. High vaccine-induced antibody titres to the circumsporozoite protein (CSP) antigen have been associated with protection from infection and episodes of clinical malaria.
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Combinatorial effects of malaria season, iron deficiency, and inflammation determine plasma hepcidin concentration in African children.
Blood
PUBLISHED: 03-04-2014
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Hepcidin is the master regulatory hormone that governs iron homeostasis and has a role in innate immunity. Although hepcidin has been studied extensively in model systems, there is less information on hepcidin regulation in global health contexts where iron deficiency (ID), anemia, and high infectious burdens (including malaria) all coexist but fluctuate over time. We evaluated iron status, hepcidin levels, and determinants of hepcidin in 2 populations of rural children aged ?8 years, in the Gambia and Kenya (total n = 848), at the start and end of a malaria season. Regression analyses and structural equation modeling demonstrated, for both populations, similar combinatorial effects of upregulating stimuli (iron stores and to a lesser extent inflammation) and downregulating stimuli (erythropoietic drive) on hepcidin levels. However, malaria season was also a significant factor and was associated with an altered balance of these opposing factors. Consistent with these changes, hepcidin levels were reduced whereas the prevalence of ID was increased at the end of the malaria season. More prevalent ID and lower hepcidin likely reflect an enhanced requirement for iron and an ability to efficiently absorb it at the end of the malaria season. These results, therefore, have implications for ID and malaria control programs.
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Use of an automated blood culture system (BD BACTEC™) for diagnosis of prosthetic joint infections: easy and fast.
BMC Infect. Dis.
PUBLISHED: 01-02-2014
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For the diagnosis of prosthetic joint infection (PJI) automated BACTEC™ blood culture bottle methods have comparable sensitivity, specificity and a shorter time to positivity than traditional cooked meat enrichment broth methods. We evaluate the culture incubation period required to maximise sensitivity and specificity of microbiological diagnosis, and the ability of BACTEC™ to detect slow growing Propionibacteria spp.
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Plasmodium falciparum malaria in children aged 0-2 years: the role of foetal haemoglobin and maternal antibodies to two asexual malaria vaccine candidates (MSP3 and GLURP).
PLoS ONE
PUBLISHED: 01-01-2014
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Children below six months are reported to be less susceptible to clinical malaria. Maternally derived antibodies and foetal haemoglobin are important putative protective factors. We examined antibodies to Plasmodium falciparum merozoite surface protein 3 (MSP3) and glutamate-rich protein (GLURP), in children in their first two years of life in Burkina Faso and their risk of malaria.
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A genome wide association study of Plasmodium falciparum susceptibility to 22 antimalarial drugs in Kenya.
PLoS ONE
PUBLISHED: 01-01-2014
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Drug resistance remains a chief concern for malaria control. In order to determine the genetic markers of drug resistant parasites, we tested the genome-wide associations (GWA) of sequence-based genotypes from 35 Kenyan P. falciparum parasites with the activities of 22 antimalarial drugs.
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Malaria vaccines: past, present and future.
Arch. Dis. Child.
PUBLISHED: 09-23-2013
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The currently available malaria control tools have allowed malaria elimination in many regions but there remain many regions where malaria control has made little progress. A safe and protective malaria vaccine would be a huge asset for malaria control. Despite the many challenges, efforts continue to design and evaluate malaria vaccine candidates. These candidates target different stages in the life cycle of Plasmodia. The most advanced vaccine candidates target the pre-erythrocytic stages in the life cycle of the parasite and include RTS,S/AS01, which has progressed through clinical development to the stage that it may be licensed in 2015. Attenuated whole-parasite vaccine candidates are highly protective, but there are challenges to manufacture and to administration. Cellular immunity is targeted by the prime-boost approach. Priming vectors trigger only modest responses but these are focused on the recombinant antigen. Boosting vectors trigger strong but broad non-specific responses. The heterologous sequence produces strong immunological responses to the recombinant antigen. Candidates that target the blood stages of the parasite have to result in an immune response that is more effective than the response to an infection to abort or control the infection of merozoites and hence disease. Finally, the sexual stages of the parasite offer another target for vaccine development, which would prevent the transmission of malaria. Today it seems unlikely that any candidate targeting a single antigen will provide complete protection against an organism of the complexity of Plasmodium. A systematic search for vaccine targets and combinations of antigens may be a more promising approach.
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Peripheral blood monocyte-to-lymphocyte ratio at study enrollment predicts efficacy of the RTS,S malaria vaccine: analysis of pooled phase II clinical trial data.
BMC Med
PUBLISHED: 05-22-2013
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RTS,S is the most advanced candidate malaria vaccine but it is only partially protective and the causes of inter-individual variation in efficacy are poorly understood. Here, we investigated whether peripheral blood monocyte-to-lymphocyte ratios (ML ratio), previously shown to correlate with clinical malaria risk, could account for differences in RTS,S efficacy among phase II trial participants in Africa.
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Comparison of modeling methods to determine liver-to-blood inocula and parasite multiplication rates during controlled human malaria infection.
J. Infect. Dis.
PUBLISHED: 04-09-2013
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Controlled human malaria infection is used to measure efficacy of candidate malaria vaccines before field studies are undertaken. Mathematical modeling using data from quantitative polymerase chain reaction (qPCR) parasitemia monitoring can discriminate between vaccine effects on the parasites liver and blood stages. Uncertainty regarding the most appropriate modeling method hinders interpretation of such trials. We used qPCR data from 267 Plasmodium falciparum infections to compare linear, sine-wave, and normal-cumulative-density-function models. We find that the parameters estimated by these models are closely correlated, and their predictive accuracy for omitted data points was similar. We propose that future studies include the linear model.
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Four-year efficacy of RTS,S/AS01E and its interaction with malaria exposure.
N. Engl. J. Med.
PUBLISHED: 03-22-2013
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The candidate malaria vaccine RTS,S/AS01E has entered phase 3 trials, but data on long-term outcomes are limited.
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Efficacy of RTS,S malaria vaccines: individual-participant pooled analysis of phase 2 data.
Lancet Infect Dis
PUBLISHED: 03-01-2013
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The efficacy of RTS,S/AS01 as a vaccine for malaria is being tested in a phase 3 clinical trial. Early results show significant, albeit partial, protection against clinical malaria and severe malaria. To ascertain variations in vaccine efficacy according to covariates such as transmission intensity, choice of adjuvant, age at vaccination, and bednet use, we did an individual-participant pooled analysis of phase 2 clinical data.
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Feedback of research findings for vaccine trials: experiences from two malaria vaccine trials involving healthy children on the Kenyan Coast.
Dev World Bioeth
PUBLISHED: 02-21-2013
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Internationally, calls for feedback of findings to be made an ethical imperative or mandatory have been met with both strong support and opposition. Challenges include differences in issues by type of study and context, disentangling between aggregate and individual study results, and inadequate empirical evidence on which to draw. In this paper we present data from observations and interviews with key stakeholders involved in feeding back aggregate study findings for two Phase II malaria vaccine trials among children under the age of 5 years old on the Kenyan Coast. In our setting, feeding back of aggregate findings was an appreciated set of activities. The inclusion of individual results was important from the point of view of both participants and researchers, to reassure participants of trial safety, and to ensure that positive results were not over-interpreted and that individual level issues around blinding and control were clarified. Feedback sessions also offered an opportunity to re-evaluate and re-negotiate trial relationships and benefits, with potentially important implications for perceptions of and involvement in follow-up work for the trials and in future research. We found that feedback of findings is a complex but key step in a continuing set of social interactions between community members and research staff (particularly field staff who work at the interface with communities), and among community members themselves; a step which needs careful planning from the outset. We agree with others that individual and aggregate results need to be considered separately, and that for individual results, both the nature and value of the information, and the context, including social relationships, need to be taken into account.
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Safety and immunogenicity of heterologous prime-boost immunisation with Plasmodium falciparum malaria candidate vaccines, ChAd63 ME-TRAP and MVA ME-TRAP, in healthy Gambian and Kenyan adults.
PLoS ONE
PUBLISHED: 01-24-2013
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Heterologous prime boost immunization with chimpanzee adenovirus 63 (ChAd63) and Modified vaccinia Virus Ankara (MVA) vectored vaccines is a strategy recently shown to be capable of inducing strong cell mediated responses against several antigens from the malaria parasite. ChAd63-MVA expressing the Plasmodium falciparum pre-erythrocytic antigen ME-TRAP (multiple epitope string with thrombospondin-related adhesion protein) is a leading malaria vaccine candidate, capable of inducing sterile protection in malaria naïve adults following controlled human malaria infection (CHMI).
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The ratio of monocytes to lymphocytes in peripheral blood correlates with increased susceptibility to clinical malaria in Kenyan children.
PLoS ONE
PUBLISHED: 01-21-2013
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Plasmodium falciparum malaria remains a major cause of illness and death in sub-Saharan Africa. Young children bear the brunt of the disease and though older children and adults suffer relatively fewer clinical attacks, they remain susceptible to asymptomatic P. falciparum infection. A better understanding of the host factors associated with immunity to clinical malaria and the ability to sustain asymptomatic P. falciparum infection will aid the development of improved strategies for disease prevention.
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A threshold concentration of anti-merozoite antibodies is required for protection from clinical episodes of malaria.
Vaccine
PUBLISHED: 01-04-2013
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Antibodies to selected Plasmodium falciparum merozoite antigens are often reported to be associated with protection from malaria in one epidemiological cohort, but not in another. Here, we sought to understand this paradox by exploring the hypothesis that a threshold concentration of antibodies is necessary for protection. We analyzed data from two independent cohorts along the Kenyan coast, one in which antibodies to AMA1, MSP-2 and MSP-3 were associated with protection from malaria (Chonyi) and another in which this association was not observed (Junju). We used a malaria reference reagent to standardize antibody measurements across both cohorts, and applied statistical methods to derive the threshold concentration of antibodies against each antigen that best correlated with a reduced risk of malaria (the protective threshold), in the Chonyi cohort. We then tested whether antibodies in Junju reached the protective threshold concentrations observed in the Chonyi cohort. Except for children under 3 years, the age-matched proportions of children achieving protective threshold concentrations of antibodies against AMA1 and MSP-2 were significantly lower in Junju compared to Chonyi (Fishers exact test, P<0.01). For MSP-3, this difference was significant only among 4-5 year olds. We conclude that although antibodies are commonly detected in malaria endemic populations, they may be present in concentrations that are insufficient for protection. Our results have implications for the analysis and interpretation of similar data from immuno-epidemiological studies.
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The relationship between RTS,S vaccine-induced antibodies, CD4? T cell responses and protection against Plasmodium falciparum infection.
PLoS ONE
PUBLISHED: 01-01-2013
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Vaccination with the pre-erythrocytic malaria vaccine RTS,S induces high levels of antibodies and CD4(+) T cells specific for the circumsporozoite protein (CSP). Using a biologically-motivated mathematical model of sporozoite infection fitted to data from malaria-naive adults vaccinated with RTS,S and subjected to experimental P. falciparum challenge, we characterised the relationship between antibodies, CD4(+) T cell responses and protection from infection. Both anti-CSP antibody titres and CSP-specific CD4(+) T cells were identified as immunological surrogates of protection, with RTS,S induced anti-CSP antibodies estimated to prevent 32% (95% confidence interval (CI) 24%-41%) of infections. The addition of RTS,S-induced CSP-specific CD4(+) T cells was estimated to increase vaccine efficacy against infection to 40% (95% CI, 34%-48%). This protective efficacy is estimated to result from a 96.1% (95% CI, 93.4%-97.8%) reduction in the liver-to-blood parasite inoculum, indicating that in volunteers who developed P. falciparum infection, a small number of parasites (often the progeny of a single surviving sporozoite) are responsible for breakthrough blood-stage infections.
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First results of phase 3 trial of RTS,S/AS01 malaria vaccine in African children.
Selidji Todagbe Agnandji, Bertrand Lell, Solange Solmeheim Soulanoudjingar, José Francisco Fernandes, Béatrice Peggy Abossolo, Cornelia Conzelmann, Barbara Gaelle Nfono Ondo Methogo, Yannick Doucka, Arnaud Flamen, Benjamin Mordmüller, Saadou Issifou, Peter Gottfried Kremsner, Jahit Sacarlal, Pedro Aide, Miguel Lanaspa, John J Aponte, Arlindo Nhamuave, Diana Quelhas, Quique Bassat, Sofia Mandjate, Eusébio Macete, Pedro Alonso, Salim Abdulla, Nahya Salim, Omar Juma, Mwanajaa Shomari, Kafuruki Shubis, Francisca Machera, Ali Said Hamad, Rose Minja, Ali Mtoro, Alma Sykes, Saumu Ahmed, Alwisa Martin Urassa, Ali Mohammed Ali, Grace Mwangoka, Marcel Tanner, Halidou Tinto, Umberto D'Alessandro, Hermann Sorgho, Innocent Valea, Marc Christian Tahita, William Kaboré, Sayouba Ouédraogo, Yara Sandrine, Robert Tinga Guiguemdé, Jean Bosco Ouédraogo, Mary J Hamel, Simon Kariuki, Chris Odero, Martina Oneko, Kephas Otieno, Norbert Awino, Jackton Omoto, John Williamson, Vincent Muturi-Kioi, Kayla F Laserson, Laurence Slutsker, Walter Otieno, Lucas Otieno, Otsyula Nekoye, Stacey Gondi, Allan Otieno, Bernhards Ogutu, Ruth Wasuna, Victorine Owira, David Jones, Agnes Akoth Onyango, Patricia Njuguna, Roma Chilengi, Pauline Akoo, Christine Kerubo, Jesse Gitaka, Charity Maingi, Trudie Lang, Ally Olotu, Benjamin Tsofa, Philip Bejon, Norbert Peshu, Kevin Marsh, Seth Owusu-Agyei, Kwaku Poku Asante, Kingsley Osei-Kwakye, Owusu Boahen, Samuel Ayamba, Kingsley Kayan, Ruth Owusu-Ofori, David Dosoo, Isaac Asante, George Adjei, Daniel Chandramohan, Brian Greenwood, John Lusingu, Samwel Gesase, Anangisye Malabeja, Omari Abdul, Hassan Kilavo, Coline Mahende, Edwin Liheluka, Martha Lemnge, Thor Theander, Chris Drakeley, Daniel Ansong, Tsiri Agbenyega, Samuel Adjei, Harry Owusu Boateng, Theresa Rettig, John Bawa, Justice Sylverken, David Sambian, Alex Agyekum, Larko Owusu, Francis Martinson, Irving Hoffman, Tisungane Mvalo, Portia Kamthunzi, Ruthendo Nkomo, Albans Msika, Allan Jumbe, Nelecy Chome, Dalitso Nyakuipa, Joseph Chintedza, W Ripley Ballou, Myriam Bruls, Joe Cohen, Yolanda Guerra, Erik Jongert, Didier Lapierre, Amanda Leach, Marc Lievens, Opokua Ofori-Anyinam, Johan Vekemans, Terrell Carter, Didier Leboulleux, Christian Loucq, Afiya Radford, Barbara Savarese, David Schellenberg, Marla Sillman, Preeti Vansadia, .
N. Engl. J. Med.
PUBLISHED: 10-18-2011
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An ongoing phase 3 study of the efficacy, safety, and immunogenicity of candidate malaria vaccine RTS,S/AS01 is being conducted in seven African countries.
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Circumsporozoite-specific T cell responses in children vaccinated with RTS,S/AS01E and protection against P falciparum clinical malaria.
PLoS ONE
PUBLISHED: 07-11-2011
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RTS,S/AS01(E) is the lead candidate pre-erythrocytic malaria vaccine. In Phase IIb field trials the safety profile was acceptable and the efficacy was 53% (95%CI 31%-72%) for protecting children against clinical malaria caused by P. falciparum. We studied CS-specific T cell responses in order to identify correlates of protection.
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Effect of the pre-erythrocytic candidate malaria vaccine RTS,S/AS01E on blood stage immunity in young children.
J. Infect. Dis.
PUBLISHED: 06-02-2011
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RTS,S/AS01(E) is the lead candidate malaria vaccine and confers pre-erythrocytic immunity. Vaccination may therefore impact acquired immunity to blood-stage malaria parasites after natural infection.
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Serial measurement of the C-reactive protein is a poor predictor of treatment outcome in prosthetic joint infection.
J. Antimicrob. Chemother.
PUBLISHED: 05-11-2011
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Prosthetic joint infection is usually treated using surgery and antibiotics. The response to the treatment regimen is often evaluated using serial monitoring of plasma C-reactive protein (CRP) concentrations. In order to examine how useful this monitoring is, we calculated the sensitivity and specificity of CRP concentrations for predicting treatment failure.
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Acute seizures attributable to falciparum malaria in an endemic area on the Kenyan coast.
Brain
PUBLISHED: 04-10-2011
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Falciparum malaria is an important cause of acute symptomatic seizures in children admitted to hospitals in sub-Saharan Africa, and these seizures are associated with neurological disabilities and epilepsy. However, it is difficult to determine the proportion of seizures attributable to malaria in endemic areas since a significant proportion of asymptomatic children have malaria parasitaemia. We studied children aged 0-13 years who had been admitted with a history of seizures to a rural Kenyan hospital between 2002 and 2008. We examined the changes in the incidence of seizures with the reduction of malaria. Logistic regression was used to model malaria-attributable fractions for seizures (the proportion of seizures caused by malaria) to determine if the observed decrease in acute symptomatic seizures was a measure of seizures that are attributable to malaria. The overall incidence of acute symptomatic seizures over the period was 651/100,000/year (95% confidence interval 632-670) and it was 400/100,000/year (95% confidence interval 385-415) for acute complex symptomatic seizures (convulsive status epilepticus, repetitive or focal) and 163/100,000/year (95% confidence interval 154-173) for febrile seizures. From 2002 to 2008, the incidence of all acute symptomatic seizures decreased by 809/100,000/year (69.2%) with 93.1% of this decrease in malaria-associated seizures. The decrease in the incidence of acute complex symptomatic seizures during the period was 111/100,000/year (57.2%) for convulsive status epilepticus, 440/100,000/year (73.7%) for repetitive seizures and 153/100,000/year (80.5%) for focal seizures. The adjusted malaria-attributable fractions for seizures with parasitaemia were 92.9% (95% confidence interval 90.4-95.1%) for all acute symptomatic seizures, 92.9% (95% confidence interval 89.4-95.5%) for convulsive status epilepticus, 93.6% (95% confidence interval 90.9-95.9%) for repetitive seizures and 91.8% (95% confidence interval 85.6-95.5%) for focal seizures. The adjusted malaria-attributable fractions for seizures in children above 6 months of age decreased with age. The observed decrease in all acute symptomatic seizures (809/100?000/year) was similar to the predicted decline (794/100,000/year) estimated by malaria-attributable fractions at the beginning of the study. In endemic areas, falciparum malaria is the most common cause of seizures and the risk for seizures in malaria decreases with age. The reduction in malaria has decreased the burden of seizures that are attributable to malaria and this could lead to reduced neurological disabilities and epilepsy in the area.
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Assessment of severe malaria in a multicenter, phase III, RTS, S/AS01 malaria candidate vaccine trial: case definition, standardization of data collection and patient care.
Malar. J.
PUBLISHED: 03-03-2011
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An effective malaria vaccine, deployed in conjunction with other malaria interventions, is likely to substantially reduce the malaria burden. Efficacy against severe malaria will be a key driver for decisions on implementation. An initial study of an RTS, S vaccine candidate showed promising efficacy against severe malaria in children in Mozambique. Further evidence of its protective efficacy will be gained in a pivotal, multi-centre, phase III study. This paper describes the case definitions of severe malaria used in this study and the programme for standardized assessment of severe malaria according to the case definition.
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Statistical methodology for the evaluation of vaccine efficacy in a phase III multi-centre trial of the RTS, S/AS01 malaria vaccine in African children.
Malar. J.
PUBLISHED: 03-03-2011
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There has been much debate about the appropriate statistical methodology for the evaluation of malaria field studies and the challenges in interpreting data arising from these trials.
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Serological evidence of discrete spatial clusters of Plasmodium falciparum parasites.
PLoS ONE
PUBLISHED: 03-01-2011
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Malaria transmission may be considered to be homogenous with well-mixed parasite populations (as in the classic Ross/Macdonald models). Marked fine-scale heterogeneity of transmission has been observed in the field (i.e., over a few kilometres), but there are relatively few data on the degree of mixing. Since the Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) is highly polymorphic, the hosts serological responses may be used to infer exposure to parasite sub-populations.
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Clearance of asymptomatic P. falciparum Infections Interacts with the number of clones to predict the risk of subsequent malaria in Kenyan children.
PLoS ONE
PUBLISHED: 01-17-2011
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Protective immunity to malaria is acquired after repeated infections in endemic areas. Asymptomatic multiclonal P. falciparum infections are common and may predict host protection. Here, we have investigated the effect of clearing asymptomatic infections on the risk of clinical malaria.
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Defining clinical malaria: the specificity and incidence of endpoints from active and passive surveillance of children in rural Kenya.
PLoS ONE
PUBLISHED: 07-30-2010
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Febrile malaria is the most common clinical manifestation of P. falciparum infection, and is often the primary endpoint in clinical trials and epidemiological studies. Subjective and objective fevers are both used to define the endpoint, but have not been carefully compared, and the relative incidence of clinical malaria by active and passive case detection is unknown.
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Safety of the malaria vaccine candidate, RTS,S/AS01E in 5 to 17 month old Kenyan and Tanzanian Children.
PLoS ONE
PUBLISHED: 07-19-2010
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The malaria vaccine candidate, RTS,S/AS01(E), showed promising protective efficacy in a trial of Kenyan and Tanzanian children aged 5 to 17 months. Here we report on the vaccines safety and tolerability. The experimental design was a Phase 2b, two-centre, double-blind (observer- and participant-blind), randomised (1?1 ratio) controlled trial. Three doses of study or control (rabies) vaccines were administered intramuscularly at 1 month intervals. Solicited adverse events (AEs) were collected for 7 days after each vaccination. There was surveillance and reporting for unsolicited adverse events for 30 days after each vaccination. Serious adverse events (SAEs) were recorded throughout the study period which lasted for 14 months after dose 1 in Korogwe, Tanzania and an average of 18 months post-dose 1 in Kilifi, Kenya. Blood samples for safety monitoring of haematological, renal and hepatic functions were taken at baseline, 3, 10 and 14 months after dose 1. A total of 894 children received RTS,S/AS01(E) or rabies vaccine between March and August 2007. Overall, children vaccinated with RTS,S/AS01(E) had fewer SAEs (51/447) than children in the control group (88/447). One SAE episode in a RTS,S/AS01(E) recipient and nine episodes among eight rabies vaccine recipients met the criteria for severe malaria. Unsolicited AEs were reported in 78% of subjects in the RTS,S/AS01(E) group and 74% of subjects in the rabies vaccine group. In both vaccine groups, gastroenteritis and pneumonia were the most frequently reported unsolicited AE. Fever was the most frequently observed solicited AE and was recorded after 11% of RTS,S/AS01(E) doses compared to 31% of doses of rabies vaccine. The candidate vaccine RTS,S/AS01(E) showed an acceptable safety profile in children living in a malaria-endemic area in East Africa. More data on the safety of RTS,S/AS01(E) will become available from the Phase 3 programme.
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Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
PLoS Med.
PUBLISHED: 03-22-2010
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Infectious diseases often demonstrate heterogeneity of transmission among host populations. This heterogeneity reduces the efficacy of control strategies, but also implies that focusing control strategies on "hotspots" of transmission could be highly effective.
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Interactions between age and ITN use determine the risk of febrile malaria in children.
PLoS ONE
PUBLISHED: 09-22-2009
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Control measures which reduce individual exposure to malaria are expected to reduce disease, but also to eventually reduce immunity. Reassuringly, long term data following community wide ITN distribution show sustained benefits at a population level. However, the more common practice in Sub-Saharan Africa is to target ITN distribution on young children. There are few data on the long term outcomes of this practice.
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Malaria vaccine development: lessons from the field.
Eur. J. Immunol.
PUBLISHED: 08-13-2009
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Studies and trials in the field are key to the development of a vaccine for malaria. Our limited knowledge of naturally acquired immunity and of transmission dynamics and disease causation in the field imposes limitations on our ability to predict the efficacy of candidate vaccinations, and the eventual outcome on deploying an efficacious vaccine at a population level.
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Multiple functions of human T cells generated by experimental malaria challenge.
Eur. J. Immunol.
PUBLISHED: 08-07-2009
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Protective immunity generated following malaria infection may be comprised of Ab or T cells against malaria Ag of different stages; however, the short-lived immunity that is observed suggests deficiency in immune memory or regulatory activity. In this study, cellular immune responses were investigated in individuals receiving Plasmodium falciparum sporozoite challenge by the natural (mosquito bite) route as part of a malaria vaccine efficacy trial. Parasitemia, monitored by blood film microscopy and PCR, was subsequently cleared with drugs. All individuals demonstrated stable IFN-gamma, IL-2 and IL-4 ex vivo ELISPOT effector responses against P. falciparum-infected RBC (iRBC) Ag, 28 and 90 days after challenge. However, infected RBC-specific central memory responses, as measured by IFN-gamma cultured ELISPOT, were low and unstable over time, despite CD4(+) T cells being highly proliferative by CFSE dilution, and showed an inverse relationship to parasite density. In support of the observation of poor memory, co-culture experiments showed reduced responses to common recall Ag, indicating malaria-specific regulatory activity. This activity could not be accounted for by the expression of IL-10, TGF-beta, FOXP3 or CTLA-4, but proliferating T cells expressed high levels of CD95, indicating a pro-apoptotic phenotype. Lastly, there was an inverse relationship between FOXP3 expression, when measured 10 days after challenge, and ex vivo IFN-gamma measured more than 100 days later. This study shows that malaria infection elicits specific Th1 and Th2 effector cells, but concomitant weak central memory and regulatory activity, which may help to explain the short-lived immunity observed.
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HIV infection, malnutrition, and invasive bacterial infection among children with severe malaria.
Clin. Infect. Dis.
PUBLISHED: 06-25-2009
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Human immunodeficiency virus (HIV) infection, malnutrition, and invasive bacterial infection (IBI) are reported among children with severe malaria. However, it is unclear whether their cooccurrence with falciparum parasitization and severe disease happens by chance or by association among children in areas where malaria is endemic.
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What you see is not what you get: implications of the brevity of antibody responses to malaria antigens and transmission heterogeneity in longitudinal studies of malaria immunity.
Malar. J.
PUBLISHED: 06-22-2009
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A major handicap in developing a malaria vaccine is the difficulty in pinpointing the immune responses that protect against malaria. The protective efficacy of natural or vaccine-induced immune responses against malaria is normally assessed by relating the level of the responses in an individual at the beginning of a follow-up period and the individuals experience of malaria infection or disease during the follow-up. This approach has identified a number of important responses against malaria, but their protective efficacies vary considerably between studies.
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Quantitative PCR evaluation of cellular immune responses in Kenyan children vaccinated with a candidate malaria vaccine.
PLoS ONE
PUBLISHED: 04-30-2009
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The T-cell mediated immune response plays a central role in the control of malaria after natural infection or vaccination. There is increasing evidence that T-cell responses are heterogeneous and that both the quality of the immune response and the balance between pro-inflammatory and regulatory T-cells determines the outcome of an infection. As Malaria parasites have been shown to induce immunosuppressive responses to the parasite and non-related antigens this study examined T-cell mediated pro-inflammatory and regulatory immune responses induced by malaria vaccination in children in an endemic area to determine if these responses were associated with vaccine immunogenicity.
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Analysis of immunity to febrile malaria in children that distinguishes immunity from lack of exposure.
Infect. Immun.
PUBLISHED: 02-17-2009
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In studies of immunity to malaria, the absence of febrile malaria is commonly considered evidence of "protection." However, apparent "protection" may be due to a lack of exposure to infective mosquito bites or due to immunity. We studied a cohort that was given curative antimalarials before monitoring began and documented newly acquired asymptomatic parasitemia and febrile malaria episodes during 3 months of surveillance. With increasing age, there was a shift away from febrile malaria to acquiring asymptomatic parasitemia, with no change in the overall incidence of infection. Antibodies to the infected red cell surface were associated with acquiring asymptomatic infection rather than febrile malaria or remaining uninfected. Bed net use was associated with remaining uninfected rather than acquiring asymptomatic infection or febrile malaria. These observations suggest that most uninfected children were unexposed rather than "immune." Had they been immune, we would have expected the proportion of uninfected children to rise with age and that the uninfected children would have been distinguished from children with febrile malaria by the protective antibody response. We show that removing the less exposed children from conventional analyses clarifies the effects of immunity, transmission intensity, bed nets, and age. Observational studies and vaccine trials will have increased power if they differentiate between unexposed and immune children.
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Risk factors for recurrence after Staphylococcus aureus bacteraemia. A retrospective matched case-control study.
J. Infect.
PUBLISHED: 01-19-2009
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We sought to identify risk factors for recurrence of Staphylococcus aureus bacteraemia (SAB) by auditing compliance with guidelines on its treatment in our hospital.
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Lack of avidity maturation of merozoite antigen-specific antibodies with increasing exposure to Plasmodium falciparum amongst children and adults exposed to endemic malaria in Kenya.
PLoS ONE
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Although antibodies are critical for immunity to malaria, their functional attributes that determine protection remain unclear. We tested for associations between antibody avidities to Plasmodium falciparum (Pf) antigens and age, asymptomatic parasitaemia, malaria exposure index (a distance weighted local malaria prevalence) and immunity to febrile malaria during 10-months of prospective follow up.
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A statistical interaction between circumsporozoite protein-specific T cell and antibody responses and risk of clinical malaria episodes following vaccination with RTS,S/AS01E.
PLoS ONE
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The candidate malaria vaccine RTS,S/AS01(E) provides significant but partial protection from clinical malaria. On in vitro circumsporozoite protein (CSP) peptide stimulation and intra-cellular cytokine staining of whole blood taken from 407 5-17 month-old children in a phase IIb trial of RTS,S/AS01(E), we identified significantly increased frequencies of two CSP-specific CD4+ T cells phenotypes among RTS,S/AS01(E) vaccinees (IFN?-IL2+TNF- and IFN?-IL2+TNF+ CD4+ T cells), and increased frequency of IFN?-IL2-TNF+ CD4+ T cells after natural exposure. All these T cells phenotypes were individually associated with reductions in the risk of clinical malaria, but IFN?-IL2-TNF+ CD4+ T cells independently predicted reduced risk of clinical malaria on multi-variable analysis (HR?=?0.29, 95% confidence intervals 0.15-0.54, p<0.0005). Furthermore, there was a strongly significant synergistic interaction between CSP-specific IFN?-IL2-TNF+ CD4+ T cells and anti-CSP antibodies in determining protection against clinical malaria (p?=?0.002). Vaccination strategies that combine potent cellular and antibody responses may enhance protection against malaria.
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Chronic exposure to Plasmodium falciparum is associated with phenotypic evidence of B and T cell exhaustion.
J. Immunol.
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Naturally acquired immunity to malaria develops slowly, requiring several years of repeated exposure to be effective. The cellular and molecular factors underlying this observation are only partially understood. Recent studies suggest that chronic Plasmodium falciparum exposure may induce functional exhaustion of lymphocytes, potentially impeding optimal control of infection. However, it remains unclear whether the "atypical" memory B cells (MBCs) and "exhausted" CD4 T cells described in humans exposed to endemic malaria are driven by P. falciparum per se or by other factors commonly associated with malaria, such as coinfections and malnutrition. To address this critical question we took advantage of a "natural" experiment near Kilifi, Kenya, and compared profiles of B and T cells of children living in a rural community where P. falciparum transmission is ongoing to the profiles of age-matched children living under similar conditions in a nearby community where P. falciparum transmission ceased 5 y prior to this study. We found that continuous exposure to P. falciparum drives the expansion of atypical MBCs. Persistent P. falciparum exposure was associated with an increased frequency of CD4 T cells expressing phenotypic markers of exhaustion, both programmed cell death-1 (PD-1) alone and PD-1 in combination with lymphocyte-activation gene-3 (LAG-3). This expansion of PD-1-expressing and PD-1/LAG-3-coexpressing CD4 T cells was largely confined to CD45RA(+) CD4 T cells. The percentage of CD45RA(+)CD27(+) CD4 T cells coexpressing PD-1 and LAG-3 was inversely correlated with frequencies of activated and classical MBCs. Taken together, these results suggest that P. falciparum infection per se drives the expansion of atypical MBCs and phenotypically exhausted CD4 T cells, which has been reported in other endemic areas.
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A phase 3 trial of RTS,S/AS01 malaria vaccine in African infants.
, Selidji Todagbe Agnandji, Bertrand Lell, José Francisco Fernandes, Béatrice Peggy Abossolo, Barbara Gaelle Nfono Ondo Methogo, Anita Lumeka Kabwende, Ayola Akim Adegnika, Benjamin Mordmüller, Saadou Issifou, Peter Gottfried Kremsner, Jahit Sacarlal, Pedro Aide, Miguel Lanaspa, John J Aponte, Sónia Machevo, Sozinho Acacio, Helder Bulo, Betuel Sigaúque, Eusébio Macete, Pedro Alonso, Salim Abdulla, Nahya Salim, Rose Minja, Maxmillian Mpina, Saumu Ahmed, Ali Mohammed Ali, Ali Takadir Mtoro, Ali Said Hamad, Paul Mutani, Marcel Tanner, Halidou Tinto, Umberto D'Alessandro, Hermann Sorgho, Innocent Valea, Biébo Bihoun, Issa Guiraud, Berenger Kaboré, Olivier Sombié, Robert Tinga Guiguemdé, Jean Bosco Ouédraogo, Mary J Hamel, Simon Kariuki, Martina Oneko, Chris Odero, Kephas Otieno, Norbert Awino, Meredith McMorrow, Vincent Muturi-Kioi, Kayla F Laserson, Laurence Slutsker, Walter Otieno, Lucas Otieno, Nekoye Otsyula, Stacey Gondi, Allan Otieno, Victorine Owira, Esther Oguk, George Odongo, Jon Ben Woods, Bernhards Ogutu, Patricia Njuguna, Roma Chilengi, Pauline Akoo, Christine Kerubo, Charity Maingi, Trudie Lang, Ally Olotu, Philip Bejon, Kevin Marsh, Gabriel Mwambingu, Seth Owusu-Agyei, Kwaku Poku Asante, Kingsley Osei-Kwakye, Owusu Boahen, David Dosoo, Isaac Asante, George Adjei, Evans Kwara, Daniel Chandramohan, Brian Greenwood, John Lusingu, Samwel Gesase, Anangisye Malabeja, Omari Abdul, Coline Mahende, Edwin Liheluka, Lincoln Malle, Martha Lemnge, Thor G Theander, Chris Drakeley, Daniel Ansong, Tsiri Agbenyega, Samuel Adjei, Harry Owusu Boateng, Theresa Rettig, John Bawa, Justice Sylverken, David Sambian, Anima Sarfo, Alex Agyekum, Francis Martinson, Irving Hoffman, Tisungane Mvalo, Portia Kamthunzi, Rutendo Nkomo, Tapiwa Tembo, Gerald Tegha, Mercy Tsidya, Jane Kilembe, Chimwemwe Chawinga, W Ripley Ballou, Joe Cohen, Yolanda Guerra, Erik Jongert, Didier Lapierre, Amanda Leach, Marc Lievens, Opokua Ofori-Anyinam, Aurélie Olivier, Johan Vekemans, Terrell Carter, David Kaslow, Didier Leboulleux, Christian Loucq, Afiya Radford, Barbara Savarese, David Schellenberg, Marla Sillman, Preeti Vansadia.
N. Engl. J. Med.
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The candidate malaria vaccine RTS,S/AS01 reduced episodes of both clinical and severe malaria in children 5 to 17 months of age by approximately 50% in an ongoing phase 3 trial. We studied infants 6 to 12 weeks of age recruited for the same trial.
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Memory B cells are a more reliable archive for historical antimalarial responses than plasma antibodies in no-longer exposed children.
Proc. Natl. Acad. Sci. U.S.A.
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Humans respond to foreign antigen by generating plasma Abs and memory B cells (MBCs). The Ab response then declines, sometimes to below the limit of detection. In contrast, MBCs are generally thought to be long-lived. We tested and compared Plasmodium falciparum (Pf)-specific Ab and MBC responses in two populations of children: (i) previously exposed children who had documented Pf infections several years ago, but minimal exposure since then; and (ii) persistently exposed children living in a separate but nearby endemic area. We found that although Pf-specific plasma Abs were lower in previously exposed children compared with persistently exposed children, their cognate MBCs were maintained at similar frequencies. We conclude that serological analysis by itself would greatly underestimate the true memory of Pf-specific Ab responses in previously exposed children living in areas where Pf transmission has been reduced or eliminated.
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Antigen-specific IL-2 secretion correlates with NK cell responses after immunization of Tanzanian children with the RTS,S/AS01 malaria vaccine.
J. Immunol.
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RTS,S/AS01, a vaccine targeting pre-erythrocytic stages of Plasmodium falciparum, is undergoing clinical trials. We report an analysis of cellular immune response to component Ags of RTS,S-hepatitis B surface Ag (HBs) and P. falciparum circumsporozoite (CS) protein-among Tanzanian children in a phase IIb RTS,S/AS01(E) trial. RTS,S/AS01 (E) vaccinees make stronger T cell IFN-?, CD69, and CD25 responses to HBs peptides than do controls, indicating that RTS,S boosts pre-existing HBs responses. T cell CD69 and CD25 responses to CS and CS-specific secreted IL-2 were augmented by RTS,S vaccination. Importantly, more than 50% of peptide-induced IFN-?(+) lymphocytes were NK cells, and the magnitude of the NK cell CD69 response to HBs peptides correlated with secreted IL-2 concentration. CD69 and CD25 expression and IL-2 secretion may represent sensitive markers of RTS,S-induced, CS-specific T cells. The potential for T cell-derived IL-2 to augment NK cell activation in RTS,S-vaccinated individuals, and the relevance of this for protection, needs to be explored further.
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Estimating individual exposure to malaria using local prevalence of malaria infection in the field.
PLoS ONE
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Heterogeneity in malaria exposure complicates survival analyses of vaccine efficacy trials and confounds the association between immune correlates of protection and malaria infection in longitudinal studies. Analysis may be facilitated by taking into account the variability in individual exposure levels, but it is unclear how exposure can be estimated at an individual level.
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Wind direction and proximity to larval sites determines malaria risk in Kilifi District in Kenya.
Nat Commun
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Studies of the fine-scale spatial epidemiology of malaria consistently identify malaria hotspots, comprising clusters of homesteads at high transmission intensity. These hotspots sustain transmission, and may be targeted by malaria-control programmes. Here we describe the spatial relationship between the location of Anopheles larval sites and human malaria infection in a cohort study of 642 children, aged 1-10-years-old. Our data suggest that proximity to larval sites predict human malaria infection, when homesteads are upwind of larval sites, but not when homesteads are downwind of larval sites. We conclude that following oviposition, female Anophelines fly upwind in search for human hosts and, thus, malaria transmission may be disrupted by targeting vector larval sites in close proximity, and downwind to malaria hotspots.
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