Agnès Le Port

Infections in Infants during the First 12 Months of Life: Role of Placental Malaria and Environmental Factors

Background The association between placental malaria (PM) and first peripheral parasitaemias in early infancy was assessed in Tori Bossito, a rural area of Benin with a careful attention on transmission factors at an individual level. Methodology Statistical analysis was performed on 550 infants followed weekly from birth to 12 months. Malaria transmission was assessed by anopheles human landing catches every 6 weeks in 36 sampling houses and season defined by rainfall. Each child was located by GPS and assigned to the closest anopheles sampling house. Data were analysed by survival Cox models, stratified on the possession of insecticide-treated mosquito nets (ITNs) at enrolment. Principal Findings Among infants sleeping in a house with an ITN, PM was found to be highly associated to first malaria infections, after adjusting on season, number of anopheles, antenatal care (ANC) visits and maternal severe anaemia. Infants born from a malaria infected placenta had a 2.13 fold increased risk to present a first malaria infection than those born from a non infected placenta ([1.24–3.67], p<0.01) when sleeping in a house with an ITN. The risk to present a first malaria infection was increased by 3.2 to 6.5, according to the level of anopheles exposure (moderate or high levels, compared to the absence of anopheles). Conclusions First malaria infections in early childhood can be attributed simultaneously to both PM and high levels of exposure to infected anopheles. Protective measures as Intermittent Preventive Treatment during pregnancy (IPTp) and ITNs, targeted on both mothers and infants should be reinforced, as well as the research on new drugs and insecticides. In parallel, investigations on placental malaria have to be strengthened to better understand the mechanisms involved, and thus to protect adequately the infants high risk group.

Modeling the Influence of Local Environmental Factors on Malaria Transmission in Benin and Its Implications for Cohort Study

Malaria remains endemic in tropical areas, especially in Africa. For the evaluation of new tools and to further our understanding of host-parasite interactions, knowing the environmental risk of transmission—even at a very local scale—is essential. The aim of this study was to assess how malaria transmission is influenced and can be predicted by local climatic and environmental factors. As the entomological part of a cohort study of 650 newborn babies in nine villages in the Tori Bossito district of Southern Benin between June 2007 and February 2010, human landing catches were performed to assess the density of malaria vectors and transmission intensity. Climatic factors as well as household characteristics were recorded throughout the study. Statistical correlations between Anopheles density and environmental and climatic factors were tested using a three-level Poisson mixed regression model. The results showed both temporal variations in vector density (related to season and rainfall), and spatial variations at the level of both village and house. These spatial variations could be largely explained by factors associated with the houses immediate surroundings, namely soil type, vegetation index and the proximity of a watercourse. Based on these results, a predictive regression model was developed using a leave-one-out method, to predict the spatiotemporal variability of malaria transmission in the nine villages. This study points up the importance of local environmental factors in malaria transmission and describes a model to predict the transmission risk of individual children, based on environmental and behavioral characteristics.

First malaria infections in a cohort of infants in Benin: biological, environmental and genetic determinants. Description of the study site, population methods and preliminary results

Objectives Malaria infection of the placenta during pregnancy was found to be associated with infant susceptibility to malaria. Other factors such as the intensity of malaria transmission and the nutritional status of the child might also play a role, which has not been adequately taken into account in previous studies. The aim of this study was to assess precisely the parts played by environmental, nutritional and biological determinants in first malaria infections, with a special interest in the role of placental infection. The objective of this paper is not to present final results but to outline the rationale of the study, to describe the methods used and to report baseline data. Design A cohort of infants followed with a parasitological (symptomatic and asymptomatic parasitaemia) and nutritional follow-up from birth to 18 months. Ecological, entomological and behavioural data were collected along the duration of the study. Setting A rural area in Benin with two seasonal peaks in malaria transmission. Participants 656 infants of women willing to participate in the study, giving birth in one of the three maternity clinics and living in one of the nine villages of the study area. Primary Outcome Measures The time and frequency of first malaria parasitaemias in infants, according to Plasmodium falciparum infection of the placenta. Results 11% of mothers had a malaria-infected placenta at delivery. Mosquito catches made every 6 weeks in the area showed an average annual P falciparum entomological inoculation rate of 15.5, with important time and space variations depending on villages. Similarly, the distribution of rainfalls, maximal during the two rainy seasons, was heterogeneous over the area. Conclusions Considering the multidisciplinary approach of all factors potentially influencing the malaria status of newborn babies, this study should bring evidence on the implication of placental malaria in the occurrence of first malaria infections in infants.

Relation between Plasmodium falciparum asymptomatic infection and malaria attacks in a cohort of Senegalese children

BackgroundIt is important to establish whether or not the presence of malaria parasites in peripheral blood of asymptomatic individuals is a predictor of future clinical mild malaria attacks (MMA). The aim of this study was to determine how an asymptomatic positive thick blood smear could be related to the occurrence of a MMA during the nine following days.MethodsThe study was conducted in a cohort of 569 Senegalese children, who were investigated for Plasmodium falciparum asymptomatic carriage at two different times of the transmission season, the beginning (September) and the end (November). The occurrence of MMA was investigated in asymptomatic carriers and non-carriers, every three days for nine consecutive days. Survival analysis was performed and risk estimates were calculated by Cox proportional hazards model.ResultsAt the beginning of the transmission season, 27.8% (147/529) of the children were asymptomatic carriers (ACs) and 5.4% (8/147) of MMA occurred among these, versus 1% (4/382) among non-carriers (RR = 5.32; IC = [1.56–18.15], p = 0.008). At the end of the transmission season, the frequency of asymptomatic carriers was similar to that observed at the beginning of the season (31.9%, p = 0.15), but no MMA was detected during this period.ConclusionA significant association between P. falciparum asymptomatic carriage and the occurrence of MMA at the beginning of the transmission season was demonstrated, with a five-fold increase in the risk of developing a MMA in ACs. In the context of a possible distribution of IPTc in the future, drug strategies may have dramatic consequences due to the existence of ACs (both long term and short term), as they seem to play an important role in the individual protection to malaria, in the most exposed age groups.

Prevention of Malaria during Pregnancy: Assessing the Effect of the Distribution of IPTp Through the National Policy in Benin

The efficiency of malaria prevention during pregnancy was compared between three studies in Benin for malaria infection of the placenta (MIP) and low birth weight (LBW). The first was carried out when chloroquine prophylaxis was still recommended, the second was an intermittent preventive treatment in pregnancy (IPTp) clinical trial comparing sulfadoxine pyrimetamine (SP) versus mefloquine, and the third was an observational study after SP-IPTp national implementation. We showed an association between the use of IPTp and the reduction of LBW (10% with national IPTp and 8.7% in IPTp trial versus 15.7% in pre-trial study). The effect on MIP was better in the trial (2.9% versus 11.2% and 16.7% for national IPTp and pre-trial studies, respectively). In spite of a good overall compliance with the national IPTp (with 84% of women taking at least one dose of SP), there are still failures in adherence to the directly observed therapy (DOT) scheme and needs for better training of health staff.

Mass spectrometry detection of G3m and IGHG3 alleles and follow-up of differential mother and neonate IgG3

Mass spectrometry (MS) analysis for detection of immunoglobulins (IG) of the human IgG3 subclass is described that relies on polymorphic amino acids of the heavy gamma3 chains. IgG3 is the most polymorphic human IgG subclass with thirteen G3m allotypes located on the constant CH2 and CH3 domains of the gamma3 chain, the combination of which leads to six major G3m alleles. Amino acid changes resulting of extensive sequencing previously led to the definition of 19 IGHG3 alleles that have been correlated to the G3m alleles. As a proof of concept, MS proteotypic peptides were defined which encompass discriminatory amino acids for the identification of the G3m and IGHG3 alleles. Plasma samples originating from ten individuals either homozygous or heterozygous for different G3m alleles, and including one mother and her baby (drawn sequentially from birth to 9 months of age), were analyzed. Total IgG3 were purified using affinity chromatography and then digested by a combination of AspN and trypsin proteases, and peptides of interest were detected by mass spectrometry. The sensitivity of the method was assessed by mixing variable amounts of two plasma samples bearing distinct G3m allotypes. A label-free approach using the high-performance liquid chromatography (HPLC) retention time of peptides and their MS mass analyzer peak intensity gave semi-quantitative information. Quantification was realized by selected reaction monitoring (SRM) using synthetic peptides as internal standards. The possibility offered by this new methodology to detect and quantify neo-synthesized IgG in newborns will improve knowledge on the first acquisition of antibodies in infants and constitutes a promising diagnostic tool for vertically-transmitted diseases.

Association of IL-4 and IL-10 maternal haplotypes with immune responses to P. falciparum in mothers and newborns

BackgroundParticular cytokine gene polymorphisms are involved in the regulation of the antibody production. The consequences of already described IL-4, IL-10 and IL-13 gene polymorphisms on biological parameters and antibody levels were investigated among 576 mothers at delivery and their newborns in the context of P. falciparum placental malaria infection.MethodsThe study took place in the semi-rural area of Tori-Bossito, in south-west Benin, where malaria is meso-endemic. Six biallelic polymorphisms were determined by quantitative PCR using TaqMan® Pre-Designed SNP Genotyping Assays, in IL-4 (rs2243250, rs2070874), IL-10 (rs1800896, rs1800871, rs1800872) and IL-13 (rs1800925) genes. Antibody responses directed to P. falciparum MSP-1, MSP-2, MSP-3, GLURP-R0, GLURP-R2 and AMA-1 recombinant proteins were determined by ELISA.ResultsThe maternal IL-4−590*T/IL-4+33*T haplotype (one or two copies) was associated with favorable maternal condition at delivery (high haemoglobin levels, absence of placental parasites) and one of its component, the IL-4−590TT genotype, was related to low IgG levels to MSP-1, MSP-2/3D7 and MSP-2/FC27. Inversely, the maternal IL-10−1082AA was positively associated with P. falciparum placenta infection at delivery. As a consequence, the IL-10−819*T allele (in CT and TT genotypes) as well as the IL-10−1082*A/IL-10−819*T/IL-10−592*A haplotype (one or two copies) in which it is included, were related to an increased risk for anaemia in newborns. The maternal IL-10−1082AA genotype was related to high IgG levels to MSP-2/3D7 and AMA-1 in mothers and newborns, respectively. The IL-13 gene polymorphism was only involved in the newborn’s antibody response to AMA-1.ConclusionThese data revealed that IL-4 and IL-10 maternal gene polymorphisms are likely to play a role in the regulation of biological parameters in pregnant women at delivery (anaemia, P. falciparum placenta infection) and in newborns (anaemia). Moreover, IL-4, IL-10 and IL-13 maternal gene polymorphisms were related to IgG responses to MSP-1, MSP-2/3D7 and MSP-2/FC27 in mothers as well as to AMA-1 in newborns.

Maternal anaemia at delivery and haemoglobin evolution in children during their first 18 months of life using latent class analysis.

Background Anaemia during pregnancy and at delivery is an important public health problem in low- and middle-income countries. Its association with the children’s haemoglobin level over time remains unclear. Our goals were to identify distinct haemoglobin level trajectories using latent class analysis and to assess the association between these trajectories and maternal anaemia and other risk factors. Method A prospective study of children from birth to 18 months of life was conducted in a rural setting in Tori-Bossito, Benin. The main outcome measure was the haemoglobin levels repeatedly measured at 3, 6, 9, 12, 15 and 18 months. Variables were collected from the mothers at delivery and from their children at birth and during the follow-up. The analyses were performed by means of Latent Class Analysis which has never been used for this kind of data. All the analyses were performed with Stata software, version 11.0, using the generalized linear latent and mixed model (GLLAMM) framework. Results We showed that 33.7% of children followed a low haemoglobin trajectory and 66.3% a high trajectory during the first 18 months of life. Newborn anaemia, placental malaria, malaria attack, sickle cell trait and male gender were significantly associated with a lower children’s haemoglobin level over time, whereas maternal age, children living in a polygamous family and with good feeding practices had a higher Hb level in the first18 months. We also showed that maternal anaemia was a predictor for ‘low haemoglobin level trajectory’ group membership but have no significant effect on children haemoglobin level over time. Conclusion Latent Class Analyses framework seems well suited to analyse longitudinal data under the hypothesis that different subpopulations of subjects are present in the data, each with its own set of parameters, with distinctive evolutions that themselves may reflect distinctive aetiologies.