Potential Impact of Seasonal Malaria Chemoprevention on the Acquisition of Antibodies against Glutamate-Rich Protein and Apical Membrane Antigen 1 in Children Living in Southern Senegal

Seasonal malaria chemoprevention (SMC) is defined as the intermittent administration of full treatment courses of an antimalarial drug to children during the peak of malaria transmission season with the aim of preventing malaria-associated mortality and morbidity. SMC using sulfadoxine–pyrimethamine (SP) combined with amodiaquine (AQ) is a promising strategy to control malaria morbidity in areas of highly seasonal malaria transmission. However, a concern is whether SMC can delay the natural acquisition of immunity toward malaria parasites in areas with intense SMC delivery. To investigate this, total IgG antibody (Ab) responses to Plasmodium falciparum antigens glutamate-rich protein R0 (GLURP-R0) and apical membrane antigen 1 (AMA-1) were measured by enzyme-linked immunosorbent assay in Senegalese children under the age of 10 years in 2010 living in Saraya and Velingara districts (with SMC using SP+AQ [SMC+] since 2007) and Tambacounda district (without SMC (SMC−)). For both P. falciparum antigens, total IgG response were significantly higher in the SMC− compared with the SMC+ group (for GLURP-R0, P < 0.001 and for AMA-1, P = 0.001). There was as well a nonsignificant tendency for higher percentage of positive responders in the SMC− compared with the SMC+ group (for GLURP-R0: 22.2% versus 14.4%, respectively [P = 0.06]; for AMA-1: 45.6% versus 40.0%, respectively [P = 0.24]). Results suggest that long-term malaria chemoprevention by SMC/SP+AQ have limited impact on the development of acquired immunity, as tested using the P. falciparum antigens GLURP-R0 and AMA-1. However, other factors, not measured in this study, may interfere as well.Although the incidence of malaria is declining in many parts of sub-Saharan Africa, it remains an important public health problem, especially in risk groups such as infants, children, and pregnant women. This heavy burden raises the need to optimize control tools and devise appropriate intervention schemes. Several studies have shown a sharp decline of the risk of malaria infections in these risk groups through the use of intermittent preventive treatment (IPT) with sulfadoxine–pyrimethamine (SP) in infants (IPTi),^1,2 in pregnant women (IPTp)^3,4 and by seasonal malaria chemoprevention with SP + amodiaquine (SMC/SP+AQ) of children between age of 1 and 5 years in regions with high seasonal malaria.^5,6 In infants and young children, these prophylactic strategies have been shown to protect children from episodes of malaria, anemia, and death^5,7,8 and have limited impact on drug resistance development.^9,10 Since these strategies reduce parasite exposure this may compromise the acquisition of protective immunity. Correspondingly, studies have shown a decrease in antibodies to malaria antigens after chemoprophylaxis; however, this may simply represent less parasite exposure rather than an actual loss of protective immunity.^11,12In Mozambique, chemoprophylaxis with SP did not significantly modify the development of natural immunity in infancy.¹³ In Ghana, antibodies against various Plasmodium falciparum antigens were significantly lower in children treated once with SP than in controls.¹⁴ Thus, despite its beneficial impact, mass implementation of malaria chemoprophylaxis raises concerns on whether naturally acquired immunity in treated individuals develops as in untreated ones (whether there is a rebound effect). The long-term effect of SMC/SP+AQ on immunity development in areas where this strategy has been routinely used for several years is not well documented. Thus, the aim of this study was to determine the potential impact of SMC/SP+AQ after the strategy has been implemented for 3 years on malaria immunity development in Senegalese children.Samples were collected during a cross-sectional survey in 2010 involving children under 10 years of age living in three health districts located in southern Senegal where malaria transmission is highly seasonal (see Figure 1 ). Two of these districts (Saraya and Velingara) have implemented SMC with one dose of SP+AQ on day 1 (given by the community health workers), followed by two doses of AQ on days 2 and 3 for 3 months (August–October) (see 15 Before blood sample collection, written informed consent was obtained from parents or guardian of each child. The study was approved by the Ethics Committee of Senegal named Comité National d''Ethique pour la Recherche en Santé (CNERS). During the study, if children presented to health posts with symptoms consistent with mild symptomatic malaria (temperature > 37.5°C) and a positive P. falciparum histidine-rich protein II rapid diagnostic test (Standard Diagnostics, Inc.; www.standardia.com), they were offered standard arthemisin combinaison therapy (ACT) first-line treatment (artesunate–amodiaquine) while children with severe malaria were referred to the nearest health district hospital. Finger-prick blood samples were collected from each study participants and blotted onto pre-labeled chromatographic filter paper (Whatman 3M; Maidston, Life Sciences United Kingdom), and stored with silica gel at 4°C until the serological analyses. Thick and thin blood films were also done for microscopic identification of Plasmodium species.Open in a separate windowFigure 1.Map of Senegal showing the study sites. Saraya and Velingara are districts were seasonal malaria chemoprevention (SMC) has been implemented since 2007, whereas in Tambacounda, SMC has not been implemented and thus, function as a control district.

Table 1

SP+AQ dosages in SMC

Malaria incidence in relation to rice cultivation in the irrigated Sahel of Mali

Seven repeated cross-sectional parasitological surveys, collecting a total of 13,912 blood samples, were carried out from September 1995 to February 1998 in three irrigated rice growing villages and three villages without irrigated agriculture in the area surrounding Niono, Mali. Parasite prevalence varied according to season and agricultural zone, but showed similar patterns for villages within the same zone. Overall, malaria prevalence was 47% in the villages without irrigated agriculture and 34% in the irrigated rice growing villages. In a village in the irrigated zone, and a village in the non-irrigated zone, 1067 and 608 children up to the age of 14 years, respectively, were followed in a passive malariological study for the period of 13 months. Fevers were attributed to malaria using a statistical method, taking into account the parasitaemia in afebrile controls from the cross-sectional surveys. The incidence of malaria fevers differed markedly between the two zones and over time. In the village in the irrigated zone, the incidence of malaria fevers was fairly constant over the year at 0.7 per 1000 children per day. In the village without irrigated agriculture, incidence was low during the dry season (at 0.6 per 1000 children per day), whereas it was high during the rainy season (at 3.2 per 1000 children per day). These results correspond well to the malaria transmission observed in a concurrent entomological survey. Rice cultivation in the semi-arid sub-Saharan environment altered the transmission pattern from seasonal to perennial, but reduced annual incidence more than two-fold.     

Malaria life cycle intensifies both natural selection and random genetic drift

Analysis of genome sequences of 159 isolates of Plasmodium falciparum from Senegal yields an extraordinarily high proportion (26.85%) of protein-coding genes with the ratio of nonsynonymous to synonymous polymorphism greater than one. This proportion is much greater than observed in other organisms. Also unusual is that the site-frequency spectra of synonymous and nonsynonymous polymorphisms are virtually indistinguishable. We hypothesized that the complicated life cycle of malaria parasites might lead to qualitatively different population genetics from that predicted from the classical Wright-Fisher (WF) model, which assumes a single random-mating population with a finite and constant population size in an organism with nonoverlapping generations. This paper summarizes simulation studies of random genetic drift and selection in malaria parasites that take into account their unusual life history. Our results show that random genetic drift in the malaria life cycle is more pronounced than under the WF model. Paradoxically, the efficiency of purifying selection in the malaria life cycle is also greater than under WF, and the relative efficiency of positive selection varies according to conditions. Additionally, the site-frequency spectrum under neutrality is also more skewed toward low-frequency alleles than expected with WF. These results highlight the importance of considering the malaria life cycle when applying existing population genetic tools based on the WF model. The same caveat applies to other species with similarly complex life cycles.Malaria, which is caused by the parasite Plasmodium falciparum, is one of the major causes of death worldwide. To aid the development of vaccines and drug treatments for malaria, researchers have studied the P. falciparum genome and identified genes that are essential to malaria parasites as well as genes that are related to drug-resistance phenotypes using population genetic tools (1–6). Researchers have also focused on particular genes related to drug resistance and characterized the evolutionary pathways of emerging drug resistance using Escherichia coli and Saccharomyces cerevisiae as model systems (7–10).Malaria parasites have a complex life cycle with two types of host organisms: humans and female Anopheles mosquitoes. Malaria parasites are transmitted from mosquito to humans through the bite of an infected mosquito. In the human host, the parasite reproduces asexually multiple times, and the within-human population size increases from 10 to 10² at the time of infection to 10⁸–10¹³ within a few weeks. When another female mosquito feeds on the blood of the infected human, 10–10³ malaria gametocytes are transmitted back to the mosquito host, and these immature gametes undergo maturation, fuse to form zygotes, and undergo sexual recombination and meiosis, and the resulting haploid cells reproduce asexually and form sporozooites that migrate to the salivary glands to complete the life cycle (11). These features of the malaria life cycle pose potential problems when attempting to analyze population genetic data using simpler models of life history and reproduction.Much of population genetics theory is based on the concept of a Wright–Fisher (WF) population (12, 13). In the WF model, the population size is constant, generations are nonoverlapping, and each new generation is formed by sampling parents with replacement from the current generation. The major differences between the malaria life cycle and the WF model are that each malaria life cycle includes two transmissions, multiple generations of asexual reproduction, and population expansions and bottlenecks. Before population genetic inferences can be conducted through analysis based on WF assumptions, it is necessary to determine whether the malaria life cycle is sufficiently well described by the WF model. If the life cycle impacts features of population genetics, then inferences based on conventional interpretations of the WF model may need to be adjusted.In a previous study based on only 25 parasite isolates, we observed two unusual patterns in the P. falciparum genome that had not been reported in any other organism (4). First, we observed synonymous and nonsynonymous site-frequency spectra that were more similar than expected, given that nonsynonymous sites likely experience stronger selection. Second, almost 20% of the genes showed a ratio of nonsynonymous to synonymous polymorphism (π_N/π_S) greater than 1. In Drosophila melanogaster (14), fewer than 2% of the genes have π_N/π_S greater than 1. Because nonsynonymous mutations result in changes to amino acids, they are likely to have a deleterious effect and exist in low frequencies in the population or be completely eliminated. In other organisms, the nonsynonymous site-frequency spectrum is more skewed toward low-frequency alleles than the synonymous site-frequency spectrum; examples include humans (15–17), Oryctolagus cuniculus (18), D. melanogaster (19), and Capsella grandiflora (20).Potential explanations for these unusual patterns including sequencing error and annotation error could be ruled out, and dramatically relaxed or diversifying selection for almost 20% of protein-coding genes seems unlikely. Although selection on antigens could possibly explain the high prevalence of genes with π_N greater than π_S, the nonsynonymous site-frequency spectrum is skewed toward low-frequency alleles, which is not what one would expect if frequency-dependent balancing selection explains the phenomenon. Because of the complexities of the malaria life cycle, we wondered whether the malaria life cycle itself could explain part of these unusual patterns. More recent work in Plasmodium vivax, a close relative with a similar life history to P. falciparum, also revealed large numbers of genes with π_N/π_S greater than 1 (21), supporting the idea that factors common to Plasmodium species but different from most other species may cause allele-frequency patterns that deviate from WF expectations.Although the behavior of the WF model is relatively robust to deviations from many underlying assumptions, there are examples in which the WF model is known to perform poorly. For example, it was recently shown that the effect of selection is increased relative to the WF model when the distribution of offspring number allows occasional large family sizes (22). Although Otto and Whitlock define a “fixation effective population size,” they also emphasize that it is a function of the selection coefficient when population size changes in time (23). Their results highlight the importance of studying the effect of various reproductive mechanisms on basic evolutionary outcomes. Although there has been research on the evolution of drug resistance in malaria parasites, in both mathematical models and computational simulations (24–27), it has not been ascertained whether the underlying processes of random genetic drift, natural selection, and their interactions yield outcomes in the malaria life cycle that are congruent with those of the WF model.Here, we sequenced 159 genomes of P. falciparum isolates from Senegal and studied the patterns of polymorphism. We find virtually identical site-frequency spectra for synonymous and nonsynonymous polymorphisms, and 26.85% of the protein-coding genes exhibit π_N/π_S > 1. To investigate whether the life cycle could explain the observed unusual patterns of polymorphism, we used Monte-Carlo simulations to examine how the malaria life cycle influences random genetic drift, natural selection, and their interactions. First, we compared quantities from generation to generation between a malaria model and the WF model, including the number of mutant alleles after one generation and probability of loss. Second, we considered properties on a longer time scale, including time to fixation or loss, segregation time, and probability of fixation or loss. Third, we simulated the site-frequency spectrum under a neutral model with the malaria life cycle. The flexibility of the simulation framework enables us to investigate various combinations of selection coefficients. Finally, we discuss the simulation results and suggest how the malaria life cycle could possibly lead to these unusual population genetic patterns.     

Cardiovascular disease and ABO blood-groups in Africans. Are blood-group A individuals at higher risk of ischemic disease?: A pilot study

Background

Since the discovery of the ABO blood group system by Karl Landsteiner in 1901, several reports have suggested an important involvement of the ABO blood group system in the susceptibility to thrombosis. Assessing that non-O blood groups in particular A blood group confer a higher risk of venous and arterial thrombosis than group O.Epidemiologic data are typically not available for all racial and ethnics groups.The purpose of this pilot study was to identify a link between ABO blood group and ischemic disease (ID) in Africans, and to analyze whether A blood group individuals were at higher risk of ischemic disease or not.

Is vector body size the key to reduced malaria transmission in the irrigated region of Niono, Mali?

Malaria vectors can reach very high densities in villages near irrigated rice fields in Africa, leading to the expectation that malaria should be especially prevalent there. Surprisingly, this is not always the case. In Niono, Mali, villages from nonirrigated areas have higher malaria prevalence than those within the irrigated regions, which suffer from higher mosquito numbers. One hypothesis explaining this observation is that mosquitoes from irrigated fields with high densities are inefficient vectors. This could occur if higher larval densities lead to smaller mosquitoes that suffer elevated mortality. Three predictions of the hypothesis were studied. First, the effect of larval density on larval body size was measured for both Anopheles gambiae Giles and Anopheles funestus Giles. Second, the relationship between larval and adult body size was tested. Third, evidence of an effect of adult size on survivorship in both irrigated and nonirrigated villages during the wet and dry seasons was sought. There was a modest positive relationship between densities of immatures and larval size, and a strong relationship between larval and adult size. Furthermore, adult survivorship was higher in nonirrigated areas. However, there was no effect of size on survivorship between comparable samples from both the irrigated and nonirrigated zones. Although density may have a causal relationship with reduced transmission in the irrigated areas of Niono, it is unlikely to be because higher density leads to smaller body size and lower survivorship.     

Perinatal Nurses' Experiences With and Knowledge of the Care of Incarcerated Women During Pregnancy and the Postpartum Period

Objective

To describe perinatal nurses’ experiences of caring for incarcerated women during pregnancy and the postpartum period; to assess their knowledge of the 2011 position statement Shackling Incarcerated Pregnant Women published by the Association of Women’s Health, Obstetric and Neonatal Nurses (AWHONN); and to assess their knowledge of their states’ laws regulating nonmedical restraint use, or shackling, of incarcerated women.