Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 14 de 14
Filter
3.
PLOS Glob Public Health ; 3(10): e0001852, 2023.
Article in English | MEDLINE | ID: mdl-37889878

ABSTRACT

Sudden shocks to health systems, such as the COVID-19 pandemic may disrupt health system functions. Health system functions may also influence the health system's ability to deliver in the face of sudden shocks such as the COVID-19 pandemic. We examined the impact of COVID-19 on the health financing function in Kenya, and how specific health financing arrangements influenced the health systems capacity to deliver services during the COVID-19 pandemic.We conducted a cross-sectional study in three purposively selected counties in Kenya using a qualitative approach. We collected data using in-depth interviews (n = 56) and relevant document reviews. We interviewed national level health financing stakeholders, county department of health managers, health facility managers and COVID-19 healthcare workers. We analysed data using a framework approach. Purchasing arrangements: COVID-19 services were partially subsidized by the national government, exposing individuals to out-of-pocket costs given the high costs of these services. The National Health Insurance Fund (NHIF) adapted its enhanced scheme's benefit package targeting formal sector groups to include COVID-19 services but did not make any adaptations to its general scheme targeting the less well-off in society. This had potential equity implications. Public Finance Management (PFM) systems: Nationally, PFM processes were adaptable and partly flexible allowing shorter timelines for budget and procurement processes. At county level, PFM systems were partially flexible with some resource reallocation but maintained centralized purchasing arrangements. The flow of funds to counties and health facilities was delayed and the procurement processes were lengthy. Reproductive and child health services: Domestic and donor funds were reallocated towards the pandemic response resulting in postponement of program activities and affected family planning service delivery. Universal Health Coverage (UHC) plans: Prioritization of UHC related activities was negatively impacted due the shift of focus to the pandemic response. Contrarily the strategic investments in the health sector were found to be a beneficial approach in strengthening the health system. Strengthening health systems to improve their resilience to cope with public health emergencies requires substantial investment of financial and non-financial resources. Health financing arrangements are integral in determining the extent of adaptability, flexibility, and responsiveness of health system to COVID-19 and future pandemics.

5.
BMJ Open ; 12(6): e059501, 2022 06 01.
Article in English | MEDLINE | ID: mdl-35649617

ABSTRACT

OBJECTIVES: Researchers at the KEMRI-Wellcome Trust Research Programme (KWTRP) carried out knowledge translation (KT) activities to support policy-makers as the Kenyan Government responded to the COVID-19 pandemic. We assessed the usefulness of these activities to identify the facilitators and barriers to KT and suggest actions that facilitate KT in similar settings. DESIGN: The study adopted a qualitative interview study design. SETTING AND PARTICIPANTS: Researchers at KWTRP in Kenya who were involved in KT activities during the COVID-19 pandemic (n=6) were selected to participate in key informant interviews to describe their experience. In addition, the policy-makers with whom these researchers engaged were invited to participate (n=11). Data were collected from March 2021 to August 2021. ANALYSIS: A thematic analysis approach was adopted using a predetermined framework to develop a coding structure consisting of the core thematic areas. Any other theme that emerged in the coding process was included. RESULTS: Both groups reported that the KT activities increased evidence availability and accessibility, enhanced policy-makers' motivation to use evidence, improved capacity to use research evidence and strengthened relationships. Policy-makers shared that a key facilitator of this was the knowledge products shared and the regular interaction with researchers. Both groups mentioned that a key barrier was the timeliness of generating evidence, which was exacerbated by the pandemic. They felt it was important to institutionalise KT to improve readiness to respond to public health emergencies. CONCLUSION: This study provides a real-world example of the use of KT during a public health crisis. It further highlights the need to institutionalise KT in research and policy institutions in African countries to respond readily to public health emergencies.


Subject(s)
COVID-19 , Emergencies , Humans , Kenya , Pandemics , Policy , Qualitative Research , Translational Science, Biomedical
7.
Cochrane Database Syst Rev ; 8: CD013207, 2021 08 12.
Article in English | MEDLINE | ID: mdl-34383961

ABSTRACT

BACKGROUND: The standard method of diagnosing HIV in infants and children less than 18 months is with a nucleic acid amplification test reverse transcriptase polymerase chain reaction test (NAT RT-PCR) detecting viral ribonucleic acid (RNA). Laboratory testing using the RT-PCR platform for HIV infection is limited by poor access, logistical support, and delays in relaying test results and initiating therapy in low-resource settings. The use of rapid diagnostic tests at or near the point-of-care (POC) can increase access to early diagnosis of HIV infection in infants and children less than 18 months of age and timely initiation of antiretroviral therapy (ART). OBJECTIVES: To summarize the diagnostic accuracy of point-of-care nucleic acid-based testing (POC NAT) to detect HIV-1/HIV-2 infection in infants and children aged 18 months or less exposed to HIV infection. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (until 2 February 2021), MEDLINE and Embase (until 1 February 2021), and LILACS and Web of Science (until 2 February 2021) with no language or publication status restriction. We also searched conference websites and clinical trial registries, tracked reference lists of included studies and relevant systematic reviews, and consulted experts for potentially eligible studies. SELECTION CRITERIA: We defined POC tests as rapid diagnostic tests conducted at or near the patient site. We included any primary study that compared the results of a POC NAT to a reference standard of laboratory NAT RT-PCR or total nucleic acid testing to detect the presence or absence of HIV infection denoted by HIV viral nucleic acids in infants and children aged 18 months or less who were exposed to HIV-1/HIV-2 infection. We included cross-sectional, prospective, and retrospective study designs and those that provided sufficient data to create the 2 × 2 table to calculate sensitivity and specificity. We excluded diagnostic case control studies with healthy controls. DATA COLLECTION AND ANALYSIS: We extracted information on study characteristics using a pretested standardized data extraction form. We used the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies) tool to assess the risk of bias and applicability concerns of the included studies. Two review authors independently selected and assessed the included studies, resolving any disagreements by consensus. The unit of analysis was the participant. We first conducted preliminary exploratory analyses by plotting estimates of sensitivity and specificity from each study on forest plots and in receiver operating characteristic (ROC) space. For the overall meta-analyses, we pooled estimates of sensitivity and specificity using the bivariate meta-analysis model at a common threshold (presence or absence of infection). MAIN RESULTS: We identified a total of 12 studies (15 evaluations, 15,120 participants). All studies were conducted in sub-Saharan Africa. The ages of included infants and children in the evaluations were as follows: at birth (n = 6), ≤ 12 months (n = 3), ≤ 18 months (n = 5), and ≤ 24 months (n = 1). Ten evaluations were field evaluations of the POC NAT test at the point of care, and five were laboratory evaluations of the POC NAT tests.The POC NAT tests evaluated included Alere q HIV-1/2 Detect qualitative test (recently renamed m-PIMA q HIV-1/2 Detect qualitative test) (n = 6), Xpert HIV-1 qualitative test (n = 6), and SAMBA HIV-1 qualitative test (n = 3). POC NAT pooled sensitivity and specificity (95% confidence interval (CI)) against laboratory reference standard tests were 98.6% (96.1 to 99.5) (15 evaluations, 1728 participants) and 99.9% (99.7 to 99.9) (15 evaluations, 13,392 participants) in infants and children ≤ 18 months. Risk of bias in the included studies was mostly low or unclear due to poor reporting. Five evaluations had some concerns for applicability for the index test, as they were POC tests evaluated in a laboratory setting, but there was no difference detected between settings in sensitivity (-1.3% (95% CI -4.1 to 1.5)); and specificity results were similar. AUTHORS' CONCLUSIONS: For the diagnosis of HIV-1/HIV-2 infection, we found the sensitivity and specificity of POC NAT tests to be high in infants and children aged 18 months or less who were exposed to HIV infection.


Subject(s)
HIV Infections/diagnosis , HIV-1/genetics , HIV-2/genetics , Point-of-Care Testing , Polymerase Chain Reaction/methods , Cross-Sectional Studies , Female , HIV-1/isolation & purification , HIV-2/isolation & purification , Humans , Infant , Infant, Newborn , Male , Reverse Transcriptase Polymerase Chain Reaction , Sensitivity and Specificity
8.
BMJ Glob Health ; 6(5)2021 05.
Article in English | MEDLINE | ID: mdl-33972261

ABSTRACT

BACKGROUND: The COVID-19 pandemic has led to an unprecedented global research effort to build a body of knowledge that can inform mitigation strategies. We carried out a bibliometric analysis to describe the COVID-19 research output in Africa in terms of setting, study design, research themes and author affiliation. METHODS: We searched for articles published between 1 December 2019 and 3 January 2021 from various databases including PubMed, African Journals Online, medRxiv, Collabovid, the WHO global research database and Google. All article types and study design were included. RESULTS: A total of 1296 articles were retrieved. 46.6% were primary research articles, 48.6% were editorial-type articles while 4.6% were secondary research articles. 20.3% articles used the entire continent of Africa as their study setting while South Africa (15.4%) was the most common country-focused setting. The most common research topics include 'country preparedness and response' (24.9%) and 'the direct and indirect health impacts of the pandemic' (21.6%). However, only 1.0% of articles focus on therapeutics and vaccines. 90.3% of the articles had at least one African researcher as author, 78.5% had an African researcher as first author, while 63.5% had an African researcher as last author. The University of Cape Town leads with the greatest number of first and last authors. 13% of the articles were published in medRxiv and of the studies that declared funding, the Wellcome Trust was the top funding body. CONCLUSIONS: This study highlights Africa's COVID-19 research and the continent's existing capacity to carry out research that addresses local problems. However, more studies focused on vaccines and therapeutics are needed to inform local development. In addition, the uneven distribution of research productivity among African countries emphasises the need for increased investment where needed.


Subject(s)
Bibliometrics , Biomedical Research , COVID-19 , Africa/epidemiology , COVID-19/epidemiology , Humans
9.
Cochrane Database Syst Rev ; 11: CD013787, 2020 11 19.
Article in English | MEDLINE | ID: mdl-33211319

ABSTRACT

BACKGROUND: Specific diagnostic tests to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and resulting COVID-19 disease are not always available and take time to obtain results. Routine laboratory markers such as white blood cell count, measures of anticoagulation, C-reactive protein (CRP) and procalcitonin, are used to assess the clinical status of a patient. These laboratory tests may be useful for the triage of people with potential COVID-19 to prioritize them for different levels of treatment, especially in situations where time and resources are limited. OBJECTIVES: To assess the diagnostic accuracy of routine laboratory testing as a triage test to determine if a person has COVID-19. SEARCH METHODS: On 4 May 2020 we undertook electronic searches in the Cochrane COVID-19 Study Register and the COVID-19 Living Evidence Database from the University of Bern, which is updated daily with published articles from PubMed and Embase and with preprints from medRxiv and bioRxiv. In addition, we checked repositories of COVID-19 publications. We did not apply any language restrictions. SELECTION CRITERIA: We included both case-control designs and consecutive series of patients that assessed the diagnostic accuracy of routine laboratory testing as a triage test to determine if a person has COVID-19. The reference standard could be reverse transcriptase polymerase chain reaction (RT-PCR) alone; RT-PCR plus clinical expertise or and imaging; repeated RT-PCR several days apart or from different samples; WHO and other case definitions; and any other reference standard used by the study authors. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data from each included study. They also assessed the methodological quality of the studies, using QUADAS-2. We used the 'NLMIXED' procedure in SAS 9.4 for the hierarchical summary receiver operating characteristic (HSROC) meta-analyses of tests for which we included four or more studies. To facilitate interpretation of results, for each meta-analysis we estimated summary sensitivity at the points on the SROC curve that corresponded to the median and interquartile range boundaries of specificities in the included studies. MAIN RESULTS: We included 21 studies in this review, including 14,126 COVID-19 patients and 56,585 non-COVID-19 patients in total. Studies evaluated a total of 67 different laboratory tests. Although we were interested in the diagnotic accuracy of routine tests for COVID-19, the included studies used detection of SARS-CoV-2 infection through RT-PCR as reference standard. There was considerable heterogeneity between tests, threshold values and the settings in which they were applied. For some tests a positive result was defined as a decrease compared to normal vaues, for other tests a positive result was defined as an increase, and for some tests both increase and decrease may have indicated test positivity. None of the studies had either low risk of bias on all domains or low concerns for applicability for all domains. Only three of the tests evaluated had a summary sensitivity and specificity over 50%. These were: increase in interleukin-6, increase in C-reactive protein and lymphocyte count decrease. Blood count Eleven studies evaluated a decrease in white blood cell count, with a median specificity of 93% and a summary sensitivity of 25% (95% CI 8.0% to 27%; very low-certainty evidence). The 15 studies that evaluated an increase in white blood cell count had a lower median specificity and a lower corresponding sensitivity. Four studies evaluated a decrease in neutrophil count. Their median specificity was 93%, corresponding to a summary sensitivity of 10% (95% CI 1.0% to 56%; low-certainty evidence). The 11 studies that evaluated an increase in neutrophil count had a lower median specificity and a lower corresponding sensitivity. The summary sensitivity of an increase in neutrophil percentage (4 studies) was 59% (95% CI 1.0% to 100%) at median specificity (38%; very low-certainty evidence). The summary sensitivity of an increase in monocyte count (4 studies) was 13% (95% CI 6.0% to 26%) at median specificity (73%; very low-certainty evidence). The summary sensitivity of a decrease in lymphocyte count (13 studies) was 64% (95% CI 28% to 89%) at median specificity (53%; low-certainty evidence). Four studies that evaluated a decrease in lymphocyte percentage showed a lower median specificity and lower corresponding sensitivity. The summary sensitivity of a decrease in platelets (4 studies) was 19% (95% CI 10% to 32%) at median specificity (88%; low-certainty evidence). Liver function tests The summary sensitivity of an increase in alanine aminotransferase (9 studies) was 12% (95% CI 3% to 34%) at median specificity (92%; low-certainty evidence). The summary sensitivity of an increase in aspartate aminotransferase (7 studies) was 29% (95% CI 17% to 45%) at median specificity (81%) (low-certainty evidence). The summary sensitivity of a decrease in albumin (4 studies) was 21% (95% CI 3% to 67%) at median specificity (66%; low-certainty evidence). The summary sensitivity of an increase in total bilirubin (4 studies) was 12% (95% CI 3.0% to 34%) at median specificity (92%; very low-certainty evidence). Markers of inflammation The summary sensitivity of an increase in CRP (14 studies) was 66% (95% CI 55% to 75%) at median specificity (44%; very low-certainty evidence). The summary sensitivity of an increase in procalcitonin (6 studies) was 3% (95% CI 1% to 19%) at median specificity (86%; very low-certainty evidence). The summary sensitivity of an increase in IL-6 (four studies) was 73% (95% CI 36% to 93%) at median specificity (58%) (very low-certainty evidence). Other biomarkers The summary sensitivity of an increase in creatine kinase (5 studies) was 11% (95% CI 6% to 19%) at median specificity (94%) (low-certainty evidence). The summary sensitivity of an increase in serum creatinine (four studies) was 7% (95% CI 1% to 37%) at median specificity (91%; low-certainty evidence). The summary sensitivity of an increase in lactate dehydrogenase (4 studies) was 25% (95% CI 15% to 38%) at median specificity (72%; very low-certainty evidence). AUTHORS' CONCLUSIONS: Although these tests give an indication about the general health status of patients and some tests may be specific indicators for inflammatory processes, none of the tests we investigated are useful for accurately ruling in or ruling out COVID-19 on their own. Studies were done in specific hospitalized populations, and future studies should consider non-hospital settings to evaluate how these tests would perform in people with milder symptoms.


Subject(s)
COVID-19 Testing/methods , COVID-19/diagnosis , Diagnostic Tests, Routine/methods , SARS-CoV-2/isolation & purification , Bias , Biomarkers/blood , C-Reactive Protein/analysis , COVID-19/blood , COVID-19/epidemiology , COVID-19 Testing/standards , Creatine Kinase/blood , Creatinine/blood , Diagnostic Tests, Routine/standards , Humans , Interleukin-6/blood , L-Lactate Dehydrogenase/blood , Leukocyte Count , Liver Function Tests , Lymphocyte Count , Pandemics , Platelet Count , ROC Curve , Reference Values , Reverse Transcriptase Polymerase Chain Reaction/standards , Sensitivity and Specificity , Triage
10.
AIDS Res Hum Retroviruses ; 36(12): 1010-1019, 2020 12.
Article in English | MEDLINE | ID: mdl-32935560

ABSTRACT

A primary concern of an antibody-based HIV-1 therapy is the virus' ability to rapidly escape antibody responses. Therefore, we investigated the relationships between antibody neutralization sensitivity, viral phenotype, and infectivity in 13 subtype C viruses using a HeLa transfectant-based assay. We observed that the seven tier 3 viruses exhibited higher infectivity than the tier 2 viruses, suggesting that higher neutralization resistance did not have a substantial entry cost. There was no relationship between neutralization resistance and susceptibility to entry inhibitors Maraviroc, PSC RANTES, or the fusion inhibitor T20, indicating that neutralization resistance may not alter these inhibitor target sites. By analyzing glycosylation patterns in 82 subtype C viruses, we found that the presence of an N-linked glycan motif at position N413 and its absence at N332 were the most important predictors of neutralization resistance. In a set of 200 subtype C viruses, tier 3 strains were more resistant than tier 2 or 1B viruses to several broadly neutralizing monoclonal antibodies targeting three different epitopes. This suggests that it is unlikely that resistance to antibodies targeting a single epitope drives overall resistance. In the context of an antibody-based intervention, highly resistant viruses with increased infectivity, circulating in the population, could hinder HIV-1 control since entry of tier 3 viruses is not always selected against. Therefore, for any long-term antibody-based intervention to be globally relevant, it must elicit responses that limit the occurrence of resistance.


Subject(s)
HIV Infections , HIV-1 , Antibodies, Neutralizing , Epitopes , HIV Antibodies , HIV Envelope Protein gp120 , HIV-1/immunology , Humans , Neutralization Tests
11.
Front Immunol ; 9: 2866, 2018.
Article in English | MEDLINE | ID: mdl-30619257

ABSTRACT

Passive transfer studies in humans clearly demonstrated the protective role of IgG antibodies against malaria. Identifying the precise parasite antigens that mediate immunity is essential for vaccine design, but has proved difficult. Completion of the Plasmodium falciparum genome revealed thousands of potential vaccine candidates, but a significant bottleneck remains in their validation and prioritization for further evaluation in clinical trials. Focusing initially on the Plasmodium falciparum merozoite proteome, we used peer-reviewed publications, multiple proteomic and bioinformatic approaches, to select and prioritize potential immune targets. We expressed 109 P. falciparum recombinant proteins, the majority of which were obtained using a mammalian expression system that has been shown to produce biologically functional extracellular proteins, and used them to create KILchip v1.0: a novel protein microarray to facilitate high-throughput multiplexed antibody detection from individual samples. The microarray assay was highly specific; antibodies against P. falciparum proteins were detected exclusively in sera from malaria-exposed but not malaria-naïve individuals. The intensity of antibody reactivity varied as expected from strong to weak across well-studied antigens such as AMA1 and RH5 (Kruskal-Wallis H test for trend: p < 0.0001). The inter-assay and intra-assay variability was minimal, with reproducible results obtained in re-assays using the same chip over a duration of 3 months. Antibodies quantified using the multiplexed format in KILchip v1.0 were highly correlated with those measured in the gold-standard monoplex ELISA [median (range) Spearman's R of 0.84 (0.65-0.95)]. KILchip v1.0 is a robust, scalable and adaptable protein microarray that has broad applicability to studies of naturally acquired immunity against malaria by providing a standardized tool for the detection of antibody correlates of protection. It will facilitate rapid high-throughput validation and prioritization of potential Plasmodium falciparum merozoite-stage antigens paving the way for urgently needed clinical trials for the next generation of malaria vaccines.


Subject(s)
Malaria, Falciparum/immunology , Merozoites/immunology , Plasmodium falciparum/immunology , Protein Array Analysis/methods , Proteome/immunology , Proteomics/methods , Health Priorities , Malaria Vaccines/immunology , Malaria, Falciparum/microbiology , Merozoites/metabolism , Plasmodium falciparum/metabolism , Plasmodium falciparum/physiology , Proteome/metabolism , Protozoan Proteins/immunology , Protozoan Proteins/metabolism , Research
12.
Int J Parasitol ; 47(2-3): 153-162, 2017 02.
Article in English | MEDLINE | ID: mdl-27890694

ABSTRACT

Young infants are less susceptible to severe episodes of malaria but the targets and mechanisms of protection are not clear. Cord blood antibodies may play an important role in mediating protection but many studies have examined their association with the outcome of infection or non-severe malaria. Here, we investigated whether cord blood IgG to Plasmodium falciparum merozoite antigens and antibody-mediated effector functions were associated with reduced odds of developing severe malaria at different time points during the first year of life. We conducted a case-control study of well-defined severe falciparum malaria nested within a longitudinal birth cohort of Kenyan children. We measured cord blood total IgG levels against five recombinant merozoite antigens and antibody function in the growth inhibition activity and neutrophil antibody-dependent respiratory burst assays. We also assessed the decay of maternal antibodies during the first 6months of life. The mean antibody half-life range was 2.51months (95% confidence interval (CI): 2.19-2.92) to 4.91months (95% CI: 4.47-6.07). The rate of decline of maternal antibodies was inversely proportional to the starting concentration. The functional assay of antibody-dependent respiratory burst activity predicted significantly reduced odds of developing severe malaria during the first 6months of life (Odds ratio (OR) 0.07, 95% CI: 0.007-0.74, P=0.007). Identification of the targets of antibodies mediating antibody-dependent respiratory burst activity could contribute to the development of malaria vaccines that protect against severe episodes of malaria in early infancy.


Subject(s)
Fetal Blood/immunology , Immunoglobulin G/immunology , Malaria, Falciparum/immunology , Plasmodium falciparum/immunology , Antibodies, Protozoan/immunology , Antigens, Protozoan/immunology , Case-Control Studies , Cohort Studies , Female , Humans , Infant , Kenya , Male , Respiratory Burst , Risk Factors
13.
Infect Immun ; 84(4): 950-963, 2016 Apr.
Article in English | MEDLINE | ID: mdl-26787721

ABSTRACT

Severe malaria (SM) is a life-threatening complication of infection with Plasmodium falciparum Epidemiological observations have long indicated that immunity against SM is acquired relatively rapidly, but prospective studies to investigate its immunological basis are logistically challenging and have rarely been undertaken. We investigated the merozoite targets and antibody-mediated mechanisms associated with protection against SM in Kenyan children aged 0 to 2 years. We designed a unique prospective matched case-control study of well-characterized SM clinical phenotypes nested within a longitudinal birth cohort of children (n= 5,949) monitored over the first 2 years of life. We quantified immunological parameters in sera collected before the SM event in cases and their individually matched controls to evaluate the prospective odds of developing SM in the first 2 years of life. Anti-AMA1 antibodies were associated with a significant reduction in the odds of developing SM (odds ratio [OR] = 0.37; 95% confidence interval [CI] = 0.15 to 0.90; P= 0.029) after adjustment for responses to all other merozoite antigens tested, while those against MSP-2, MSP-3, Plasmodium falciparum Rh2 [PfRh2], MSP-119, and the infected red blood cell surface antigens were not. The combined ability of total IgG to inhibit parasite growth and mediate the release of reactive oxygen species from neutrophils was associated with a marked reduction in the odds of developing SM (OR = 0.07; 95% CI = 0.006 to 0.82;P= 0.03). Assays of these two functional mechanisms were poorly correlated (Spearman rank correlation coefficient [rs] = 0.12;P= 0.07). Our data provide epidemiological evidence that multiple antibody-dependent mechanisms contribute to protective immunity via distinct targets whose identification could accelerate the development of vaccines to protect against SM.


Subject(s)
Antibodies, Protozoan/physiology , Malaria, Falciparum/immunology , Plasmodium falciparum/physiology , Aging , Antigens, Protozoan/immunology , Case-Control Studies , Child , Child, Preschool , Growth Inhibitors/metabolism , Humans , Infant , Kenya/epidemiology , Merozoites/immunology , Odds Ratio , Respiratory Burst/physiology
14.
BMC Med ; 13: 114, 2015 May 13.
Article in English | MEDLINE | ID: mdl-25967134

ABSTRACT

BACKGROUND: Epidemiological studies indicate that some children experience many more episodes of clinical malaria than their age mates in a given location. Whether this is as a result of the micro-heterogeneity of malaria transmission with some children effectively getting more exposure to infectious mosquitoes than others, or reflects a failure in the acquisition of immunity needs to be elucidated. Here, we investigated the determinants of increased susceptibility to clinical malaria by comparing the intensity of exposure to Plasmodium falciparum and the acquisition of immunity in children at the extreme ends of the over-dispersed distribution of the incidence of clinical malaria. METHODS: The study was nested within a larger cohort in an area where the intensity of malaria transmission was low. We identified children who over a five-year period experienced 5 to 16 clinical malaria episodes (children at the tail-end of the over-dispersed distribution, n = 35), remained malaria-free (n = 12) or had a single episode (n = 26). We quantified antibodies against seven Plasmodium falciparum merozoite antigens in plasma obtained at six cross-sectional surveys spanning these five years. We analyzed the antibody responses to identify temporal dynamics that associate with disease susceptibility. RESULTS: Children experiencing multiple episodes of malaria were more likely to be parasite positive by microscopy at cross-sectional surveys (X (2) test for trend 14.72 P = 0.001) and had a significantly higher malaria exposure index, than those in the malaria-free or single episode groups (Kruskal-Wallis test P = 0.009). In contrast, the five-year temporal dynamics of anti-merozoite antibodies were similar in the three groups. Importantly in all groups, antibody levels were below the threshold concentrations previously observed to be correlated with protective immunity. CONCLUSIONS: We conclude that in the context of a low malaria transmission setting, susceptibility to clinical malaria is not accounted for by anti-merozoite antibodies but appears to be a consequence of increased parasite exposure. We hypothesize that intensive exposure is a prerequisite for protective antibody concentrations, while little to modest exposure may manifest as multiple clinical infections with low levels of antibodies. These findings have implications for interventions that effectively lower malaria transmission intensity.


Subject(s)
Malaria, Falciparum/epidemiology , Malaria, Falciparum/immunology , Animals , Antibodies, Protozoan/blood , Child , Child, Preschool , Cross-Sectional Studies , Female , Humans , Incidence , Infant , Malaria, Falciparum/transmission , Male , Plasmodium falciparum
SELECTION OF CITATIONS
SEARCH DETAIL
...