Spatial variation of life-history traits in the freshwater snail Bulinus truncatus, the intermediate host of human and cattle schistosomiasis, in relation to field application of niclosamide in northern and central Côte d’Ivoire

Abstract

Background: Control of intermediate host snails using molluscicides for the control and/or elimination of schistosomiasis is strategy in the line with WHO recommendations. Niclosamide is the main chemical molluscicide recognized by WHO. However, the extent of the application of molluscicide outside the immediate killing of the snail such as the impact on the evolution of life-history traits; in relation to recolonization of treated sites is less or not known. This study aimed to characterize the spatial variation of life-history traits in Bulinus truncatus populations in north and central Côte d’Ivoire, in relation to niclosamide spraying in the field.From 2016 to 2018, we conducted a trial to control the intermediate host snails for interrupting seasonal transmission urinary schistosomiasis in northern and central Côte d’Ivoire, using niclosamide. The molluscicide was sprayed three times per year in habitats harboring the freshwater snail B. truncatus. Snails were collected before niclosamide application and 2-3 months after the sites were treated, and also from some untreated sites. Families from six natural populations of snails were monitored for several life-history traits, including growth, fecundity and survival, under laboratory conditions, over one generation (G1).Results: Survival rate varied among populations with the highest rates observed in northern populations. No significant difference was detected between populations before and after treatment, for this trait. Numbers of eggs and eggs per capsule at first reproduction, fecundity and growth were significantly lower in treated than untreated groups. Similar finding was observed for populations of before and after treatment. Egg production also varied across populations with the highest values found in northern populations. Within treated group, a significant difference for survival rate was detected between northern and central populations. Almost all parameters of reproduction and growth varied significantly, except for the number of egg capsules.Conclusions: Our study shows a spatial variation of life-history traits in B. truncatus snails. Lower values of these traits were observed in populations from recolonized sites after treatment with niclosamide. This trend was much more perceptible in populations from central Côte d’Ivoire. Investigations should be carried out over several generations of snails in order to clarify the impact of niclosamide on their life-history traits.