Prior selfing and the selfing syndrome in animals: an experimental approach in the freshwater snail Biomphalaria pfeifferi

Inbreeding species of hermaphroditic animals practising copulation have been characterized by few copulations, no waiting time (the time that an isolated individual waits for a partner before initiating reproduction compared with paired individuals) and limited inbreeding (self-fertilization) depression. This syndrome, which has never been fully studied before in any species, is analysed here in the highly selfing freshwater snail Biomphalaria pfeifferi. We conducted an experiment under laboratory conditions over two generations (G1 and G2) using snails sampled from two populations (100 individuals per population). G1 individuals were either isolated or paired once a week (potentially allowing for crosses), and monitored during 29 weeks for growth, fecundity and survival. Very few copulations were observed in paired snails, and there was a positive correlation in copulatory activity (e.g. number of copulations) between the male and female sexual roles. The waiting time was either null or negative, meaning that isolated individuals initiated reproduction before paired ones. G2 offspring did not differ in hatching rate and survival (to 28 days) between treatments, but offspring from paired individuals grew faster than those from isolated individuals. On the whole, the self-fertilization depression was extremely low in both populations. Another important result is that paired G1 individuals began laying (selfed) eggs several weeks prior to initiating copulation: this is the first characterization of prior selfing (selfing initiated prior to any outcrossing) in a hermaphroditic animal. A significant population effect was observed on most traits studied. Our results are discussed with regard to the maintenance of low outcrossing rates in highly inbreeding specie

Sustaining control of Schistosomiasis mansoni in western Côte d'Ivoire : results from a SCORE study, one year after initial praziquantel administration

The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) has launched several large-scale trials to determine the best strategies for gaining and sustaining control of schistosomiasis and transitioning toward elimination. In Côte d'Ivoire, a 5-year cluster-randomized trial is being implemented in 75 schools to sustain the control of schistosomiasis mansoni. We report Schistosoma mansoni infection levels in children one year after the initial school-based treatment (SBT) with praziquantel and compare with baseline results to determine the effect of the intervention.; The baseline cross-sectional survey was conducted in late 2011/early 2012 and the first follow-up in May 2013. Three consecutive stool samples were collected from 9- to 12-year-old children in 75 schools at baseline and 50 schools at follow-up. Stool samples were subjected to duplicate Kato-Katz thick smears. Directly observed treatment (DOT) coverage of the SBT was assessed and the prevalence and intensity of S. mansoni infection compared between baseline and follow-up.; The S. mansoni prevalence in the 75 schools surveyed at baseline was 22.1% (95% confidence interval (CI): 19.5-24.4%). The DOT coverage was 84.2%. In the 50 schools surveyed at baseline and one year after treatment, the overall prevalence of S. mansoni infection decreased significantly from 19.7% (95% CI: 18.5-20.8%) to 12.8% (95% CI: 11.9-13.8%), while the arithmetic mean S. mansoni eggs per gram of stool (EPG) among infected children slightly increased from 92.2 EPG (95% CI: 79.2-105.3 EPG) to 109.3 EPG (95% CI: 82.7-135.9 EPG). In two of the 50 schools, the prevalence increased significantly, despite a DOT coverage of >75%.; One year after the initial SBT, the S. mansoni prevalence had decreased. Despite this positive trend, an increase was observed in some schools. Moreover, the infection intensity among S. mansoni-infected children was slightly higher at the 1-year follow-up compared to the baseline situation. Our results emphasize the heterogeneity of transmission dynamics and provide a benchmark for the future yearly follow-up surveys of this multi-year SCORE intervention study

Sustaining control of schistosomiasis mansoni in moderate endemicity areas in western Côte d'Ivoire : a SCORE study protocol

Schistosomiasis is a parasitic disease that occurs in the tropics and subtropics. The mainstay of control is preventive chemotherapy with praziquantel. In Africa, an estimated 230 million people require preventive chemotherapy. In western Côte d'Ivoire, infections with Schistosoma mansoni are widespread. To provide an evidence-base for programme decisions about preventive chemotherapy to sustain control of schistosomiasis, a 5-year multi-country study with different treatment arms has been designed by the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) and is currently being implemented in various African settings, including Côte d'Ivoire.; We report the study protocol, including ethics statement and insight from a large-scale eligibility survey carried out in four provinces in western Côte d'Ivoire. The study protocol has been approved by the ethics committees of Basel and Côte d'Ivoire. A total of 12,110 children, aged 13-14 years, from 264 villages were screened for S. mansoni using duplicate Kato-Katz thick smears from single stool samples. Among the schools with a S. mansoni prevalence of 10-24%, 75 schools were selected and randomly assigned to one of three treatment arms. In each school, three stool samples are being collected from 100 children aged 9-12 years annually and one stool sample from 100 first-year students at baseline and in the final year and subjected to duplicate Kato-Katz thick smears. Cost and coverage data for the different intervention arms, along with environmental, political and other characteristics that might impact on the infection prevalence and intensity will be recorded in each study year, using a pretested village inventory form.; The study will document changes in S. mansoni infection prevalence and intensity according to different treatment schemes. Moreover, factors that determine the effectiveness of preventive chemotherapy will be identified. These factors will help to develop reasonable measures of force of transmission that can be used to make decisions about the most cost-effective means of lowering prevalence, intensity and transmission in a given setting. The gathered information and results will inform how to effectively sustain control of schistosomiasis at a low level in different social-ecological contexts.; ISRCTN99401114 (date assigned: 12 November 2014)

Spatio-temporal population genetic structure, relative to demographic and ecological characteristics, in the freshwater snail Biomphalaria pfeifferi in Man, western Côte d'Ivoire

Combining the analysis of spatial and temporal variation when investigating population structure enhances our capacity for unravelling the biotic and abiotic factors responsible for microevolutionary change. This work aimed at measuring the spatial and temporal genetic structure of populations of the freshwater snail Biomphalaria pfeifferi (the intermediate host of the trematode Schistosoma mansoni) in relation to the mating system (self-fertilization), demography, parasite prevalence and some ecological parameters. Snail populations were sampled four times in seven human-water contact sites in the Man region, western Côte d'Ivoire, and their variability was measured at five microsatellite loci. Limited genetic diversity and high selfing rates were observed in the populations studied. We failed to reveal an effect of demographic and ecological parameters on within-population diversity, perhaps as a result of a too small number of populations. A strong spatial genetic differentiation was detected among populations. The temporal differentiation within populations was high in most populations, though lower than the spatial differentiation. All estimates of effective population size were lower than seven suggesting a strong effect of genetic drift. However, the genetic drift was compensated by high gene flow. The genetic structure within and among populations reflected that observed in other selfing snail species, relying on high selfing rates, low effective population sizes, environmental stochasticity and high gene flow

Sustaining the control of Schistosoma mansoni in western Côte d'Ivoire : baseline findings before the implementation of a randomized trial

We report baseline findings before the implementation of a 4-year intervention trial designed to assess the impact of three different school-based treatment schedules with praziquantel to sustain the control of intestinal schistosomiasis. The baseline survey was conducted in 75 schools of western Côte d'Ivoire previously identified with moderate Schistosoma mansoni endemicity (prevalence: 10-24% in children aged 13-14 years). Three stool samples collected over consecutive days were subjected to duplicate Kato-Katz thick smears each. A questionnaire was administered to collect village-specific information that is relevant for schistosomiasis transmission. Overall, 4,953 first graders (aged 5-8 years) and 7,011 school children (aged 9-12 years) had complete parasitologic data. The overall prevalence of S. mansoni was 5.4% among first graders and 22.1% in 9- to 12-year-old children. Open defecation was practiced in all villages. The current baseline findings will be important to better understand the dynamics of S. mansoni prevalence and intensity over the course of this trial that might be governed by village characteristics and specific treatment interventions

The spatial distribution of Schistosoma mansoni infection in four regions of western Côte d'Ivoire

Schistosomiasis poses a considerable public health burden in sub- Saharan Africa and a sound understanding of the spatial distribution facilitates to better target control interventions. The objectives of this study were i) to assess the prevalence of Schistosoma mansoni among school-aged children in four regions of western Côte d'Ivoire; ii) to determine demographic, climatic and environmental factors that influence the distribution of S. mansoni; and iii) to map and predict the distribution of S. mansoni in non-sampled locations. Parasitological surveys were carried out in 264 schools from June to December 2011. In each school, we aimed to examine 50 children for S. mansoni infection using duplicate Kato-Katz thick smears. Schools were georeferenced using a hand-held global positioning system receiver. Demographic data were obtained from readily available school lists, while climatic and environmental data were extracted from open-access remote sensing databases. Multivariable, binary non-spatial models and a Bayesian geostatistical logistic regression model were used to identify demographic, climatic and environmental risk factors for S. mansoni infection. Risk maps were developed based on observed S. mansoni prevalences and using Bayesian geostatistical models to predict prevalences at non-sampled locations. Overall, 12,462 children provided a sufficiently large stool sample to perform at least one Kato-Katz thick smear. The observed overall prevalence of S. mansoni infection was 39.9%, ranging from 0 to 100% at the unit of the school. Bayesian geostatistical analysis revealed that age, sex, altitude and difference between land surface temperature at day and night were significantly associated with S. mansoni infection. The S. mansoni risk map presented here is being been used by the national schistosomiasis control programme for spatial targeting of praziquantel and other interventions

Study participation of schoolchildren at the baseline survey and one-year follow-up survey.

<p>The flowcharts show the study participation of 9- to 12-year-old schoolchildren at the baseline survey (A), which was conducted from December 2011 to February 2012, and the first follow-up survey (B), which was carried out one-year post-treatment in May 2013, in western Côte d’Ivoire.</p

Dynamics of the <i>S</i>. <i>mansoni</i> infection intensity in schools of treatment arms A and B.

<p>The graphs show the change of the <i>S</i>. <i>mansoni</i> infection intensity expressed as change in arithmetic mean eggs per gram of feces (AM EPG) from the baseline survey, which was conducted from December 2011 to February 2012, to the first follow-up survey, which was carried out one-year post-treatment in May 2013, in 9- to 12-year-old schoolchildren from 25 schools per treatment arm in western Côte d’Ivoire. Arm A: schools receive praziquantel treatment annually for four years, Arm B: schools receive praziquantel treatment the first two years of the study, followed by two years of “drug holiday”. Red star: <i>S</i>. <i>mansoni</i> infection intensity decreased significantly.</p

Correlation between coverage rate and the changes in the <i>S</i>. <i>mansoni</i> infection intensity.

<p>Scatter plot illustrating the correlation between the coverage rates achieved in a directly observed school-based treatment round implemented in 50 schools in western Côte d’Ivoire in June 2012, and the % changes in the <i>S</i>. <i>mansoni</i> arithmetic mean infection intensity observed between the baseline survey, which was conducted from December 2011 to February 2012, and the first follow-up survey, which was carried out one-year post-treatment in May 2013, in 9- to 12-year-old schoolchildren.</p

Dynamics of the <i>S</i>. <i>mansoni</i> prevalence in schools of treatment arms A and B.

<p>The graphs show the change of the <i>S</i>. <i>mansoni</i> prevalence from the baseline survey, which was conducted from December 2011 to February 2012, to the first follow-up survey, which was carried out one-year post-treatment in May 2013, in 9- to 12-year-old schoolchildren from 25 schools per treatment arm in western Côte d’Ivoire. Arm A: schools receive praziquantel treatment annually for four years, Arm B: schools receive praziquantel treatment the first two years of the study, followed by two years of “drug holiday”. Red star: <i>S</i>. <i>mansoni</i> prevalence increased significantly.</p