Spatial variation of life-history traits in Bulinus truncatus, the intermediate host of schistosomes, in the context of field application of niclosamide in Côte d'Ivoire.

BACKGROUND: Control of intermediate host snails using molluscicides for the control and/or elimination of schistosomiasis is a strategy in line with WHO recommendations. Niclosamide is the main chemical molluscicide recommended by WHO. However, except the immediate killing of the snail, the extent of the impact of the molluscicide application on the evolution of snail life-history traits, in relation to recolonization of treated sites is not well known. This study aimed to characterize the spatial variation of life-history traits of populations of the freshwater snail Bulinus truncatus, in relation to niclosamide spraying in the field. From 2016 to 2018, we conducted a trial, using niclosamide to control the intermediate host snails for interrupting the seasonal transmission of urinary schistosomiasis in northern and central Côte d'Ivoire. Five villages (sites) were considered, including three test and two control villages. In the test villages, the molluscicide was sprayed in habitats harboring B. truncatus snails three times a year (November, February-March and June). We sampled six B. truncatus populations: two populations from the control villages without any treatment; one collected before treatment and three sampled 2-3 months after treatment of the site with niclosamide. The snail populations were monitored for several life-history traits, including survival, growth, fecundity and hatchability, under laboratory conditions, over one generation (G1). We tested the population, region (North/Centre) and treatment status (treated/untreated) effects on the variation of the measured life-history traits and correlations between pairs of traits were estimated. RESULTS: On the whole, the traits varied among populations. The risk of death was lower in northern populations compared to central ones. The age at first reproduction was reached earlier with a smaller size of snails in northern populations. Values of first reproduction features (size and fecundity) were lower in treated snail populations. The overall growth of untreated populations was higher than that of treated ones. The late fecundity and egg hatching were higher in northern than in central snails. At first reproduction, age was negatively correlated with some fecundity parameters. However, growth was positively associated with fecundity. CONCLUSIONS: Our study showed a spatial variation of life-history traits in B. truncatus snails. The mollusciciding seems to have led to the depression of some life-history traits in the snail populations. However, investigations should be carried out over several generations of snails to better clarify the impact of niclosamide on the evolution of the life-history traits.

Effectiveness of Four Different Interventions Against Schistosoma haematobium in a Seasonal Transmission Setting of Côte d'Ivoire: A Cluster Randomized Trial.

BACKGROUND: Annual mass drug administration (MDA) using praziquantel is the cornerstone of schistosomiasis morbidity control but is not sufficient to interrupt transmission. We implemented a cluster-randomized trial to compare the effectiveness of 4 different intervention packages to interrupt transmission of Schistosoma haematobium in a seasonal transmission setting of Côte d'Ivoire. METHODS: Sixty-four localities with a S. haematobium prevalence in school children aged 13-14 years above 4% were randomly assigned to 1 of 4 intervention arms over a 3-year period: (1) the current standard strategy consisting of annual MDA before peak of transmission, (2) annual MDA after peak of transmission, (3) biannual MDA, and (4) standard MDA combined with snail control. The primary outcome was prevalence and intensity of S. haematobium infection in children aged 9-12 years 1 year after the final intervention, using urine filtration performed by experienced microscopists. RESULTS: By study end, we observed the lowest S. haematobium prevalence in the biannual MDA, compared to the standard treatment arm (0.6% vs 7.5%; odds ratio [OR] = 0.07, 95% confidence interval [CI] = .02 to .24). The prevalence in arms 2 and 4 was about 3.5%, which was not statistically significantly different from the standard strategy (both ORs 0.4, 95% CI = .1 to ~1.8). New cases of infection were still observed in all arms at study end. CONCLUSIONS: Biannual MDA was the only regimen that outperformed the standard treatment. All strategies resulted in decreased prevalence of infection; however, none of them was able to interrupt transmission of S. haematobium within a 3-year period. CLINICAL TRIALS REGISTRATION: ISRCTN10926858.

Molecular characterization and distribution of Schistosoma cercariae collected from naturally infected bulinid snails in northern and central Côte d'Ivoire.

BACKGROUND: Accurate identification of schistosome species infecting intermediate host snails is important for understanding parasite transmission, schistosomiasis control and elimination. Cercariae emerging from infected snails cannot be precisely identified morphologically to the species level. We used molecular tools to clarify the distribution of the Schistosoma haematobium group species infecting bulinid snails in a large part of Côte d'Ivoire and confirmed the presence of interspecific hybrid schistosomes. METHODS: Between June 2016 and March 2017, Bulinus snails were sampled in 164 human-water contact sites from 22 villages of the northern and central parts of Côte d'Ivoire. Multi-locus genetic analysis (mitochondrial cox1 and nuclear ITS) was performed on individual schistosome cercariae shed from snails, in the morning and in the afternoon, for species and hybrid identification. RESULTS: Overall, 1923 Bulinus truncatus, 255 Bulinus globosus and 1424 Bulinus forskalii were obtained. Among 2417 Bulinus screened, 25 specimens (18 B. truncatus and seven B. globosus) shed schistosomes, with up to 14% infection prevalence per site and time point. Globally, infection rates per time point ranged between 0.6 and 4%. Schistosoma bovis, S. haematobium and S. bovis × S. haematobium hybrids infected 0.5%, 0.2% and 0.4% of the snails screened, respectively. Schistosoma bovis and hybrids were more prevalent in B. truncatus, whereas S. haematobium and hybrid infections were more prevalent in B. globosus. Schistosoma bovis-infected Bulinus were predominantly found in northern sites, while S. haematobium and hybrid infected snails were mainly found in central parts of Côte d'Ivoire. CONCLUSIONS: The data highlight the necessity of using molecular tools to identify and understand which schistosome species are transmitted by specific intermediate host snails. The study deepens our understanding of the epidemiology and transmission dynamics of S. haematobium and S. bovis in Côte d'Ivoire and provides the first conclusive evidence for the transmission of S. haematobium × S. bovis hybrids in this West African country. Trial registration ISRCTN, ISRCTN10926858. Registered 21 December 2016; retrospectively registered (see: http://www.isrctn.com/ISRCTN10926858 ).

Interrupting seasonal transmission of Schistosoma haematobium and control of soil-transmitted helminthiasis in northern and central Côte d'Ivoire: a SCORE study protocol.

BACKGROUND: To achieve a world free of schistosomiasis, the objective is to scale up control and elimination efforts in all endemic countries. Where interruption of transmission is considered feasible, countries are encouraged to implement a comprehensive intervention package, including preventive chemotherapy, information, education and communication (IEC), water, sanitation and hygiene (WASH), and snail control. In northern and central Côte d'Ivoire, transmission of Schistosoma haematobium is seasonal and elimination might be achieved. In a cluster-randomised trial, we will assess different treatment schemes to interrupt S. haematobium transmission and control soil-transmitted helminthiasis over a 3-year period. We will compare the impact of (i) arm A: annual mass drug administration (MDA) with praziquantel and albendazole before the peak schistosomiasis transmission season; (ii) arm B: annual MDA after the peak schistosomiasis transmission season; (iii) arm C: two yearly treatments before and after peak schistosomiasis transmission; and (iv) arm D: annual MDA before peak schistosomiasis transmission, coupled with chemical snail control using niclosamide. METHODS/DESIGN: The prevalence and intensity of S. haematobium and soil-transmitted helminth infections will be assessed using urine filtration and Kato-Katz thick smears, respectively, in six administrative regions in northern and central parts of Côte d'Ivoire. Once a year, urine and stool samples will be collected and examined from 50 children aged 5-8 years, 100 children aged 9-12 years and 50 adults aged 20-55 years in each of 60 selected villages. Changes in S. haematobium and soil-transmitted helminth prevalence and intensity will be assessed between years and stratified by intervention arm. In the 15 villages randomly assigned to intervention arm D, intermediate host snails will be collected three times per year, before niclosamide is applied to the selected freshwater bodies. The snail abundance and infection rates over time will allow drawing inference on the force of transmission. DISCUSSION: This cluster-randomised intervention trial will elucidate whether in an area with seasonal transmission, the four different treatment schemes can interrupt S. haematobium transmission and control soil-transmitted helminthiasis. Lessons learned will help to guide schistosomiasis control and elimination programmes elsewhere in Africa. TRIAL REGISTRATION: ISRCTN ISRCTN10926858 . Registered 21 December 2016. Retrospectively registered.