Intermediate Host Snails of Human Schistosomes in the Senegal River Delta: Spatial Distribution According to Physicochemical Parameters

Abstract

The objective of the study was to evaluate the influence of physicochemical parameters of water on the spatial distribution of snail intermediate hosts of human schistosomes in the Senegal River Delta. Eight water points in three endemic villages for schistosomiasis were selected for biweekly monitoring of snail numbers and physicochemical parameters of water at the beginning of the rainy season. The results show that the spatial distribution of snail populations is a function of certain parameters. The pH, the dissolved oxygen and its saturation, and the temperature have a positive influence on the Bulinus and Biomphalaria, while the conductivity, the speed of flow, and the salts (phosphates, salinity, and nitrates) seem to act negatively on the populations of these snails.

Species Diversity, Distribution, and Abundance of Freshwater Snails in KwaZulu-Natal, South Africa

“…Freshwater snails prefer habitats with pH levels ranging from 6.5-8.5 as extreme pH levels increase the solubility of elements and compounds making toxic chemicals more mobile and increasing the risk of absorption by aquatic life and leading to death. In this study, snails were found in sites with pH levels ranging from 6.42-7.98, which falls within the favorable range for surface water [38]. A significant positive correlation was recorded between pH, B. globosus, and T. granifera, while a negative correlation was recorded with B. tropicus, B. forskalii, L. natalensis, bivalves, and P. acuta.…”

“…This could be because there were heavy rains prior to sampling and hence floods or fast flowing water may have swept away many freshwater snails and food causing major fluctuations in the population density [36]. In addition, snail abundance and diversity reduce with high rainfall as snails cannot attach themselves to rocks or water vegetation and are washed away by the high velocities (>0.3 ms −1 ) of flowing water [37,38]. On the other hand, B. globosus, B. forskalii, and T. granifera showed a positive correlation, and this could be because of snail abundance and diversity increase with low rainfall or at the beginning of the rainy season [37,38].…”

“…In addition, snail abundance and diversity reduce with high rainfall as snails cannot attach themselves to rocks or water vegetation and are washed away by the high velocities (>0.3 ms −1 ) of flowing water [37,38]. On the other hand, B. globosus, B. forskalii, and T. granifera showed a positive correlation, and this could be because of snail abundance and diversity increase with low rainfall or at the beginning of the rainy season [37,38]. This is consistent with literature showing that B. globosus is positively correlated with rainfall [39].…”

Seasonal and environmental dynamics of intra-urban freshwater habitats and their influence on the abundance of Bulinus snail host of Schistosoma haematobium in the Tiko endemic focus, Mount Cameroon region

“…The abundance of Bulinus and Physa was positively correlated although Physa was the most abundant freshwater snail species in Tiko. Some studies have shown a positive correlation between other freshwater snails ( Tarebia granifera ) and Bulinus globosus [ 67 , 68 ] whereas a recent study showed a negative correlation, though not significant, between B . globosus and the invasive Physa acuta [ 69 ].…”

“…The abundance of Bulinus and Physa was positively correlated although Physa was the most abundant freshwater snail species in Tiko. Some studies have shown a positive correlation between other freshwater snails (Tarebia granifera) and Bulinus globosus [67,68] whereas a recent study showed a negative correlation, though not significant, between B. globosus and the invasive Physa acuta [69]. This finding has implication for further investigation as research has shown that P. acuta has higher fecundity, shorter hatching time, higher salinity tolerance, higher temperature tolerance, and tolerates fast current velocities up to 0.6 ms -1 compared to other pulmonates that are not found in water exceeding the velocity of 0.3 ms -1 [70].…”