Geographical Distribution of Biomphalaria snails in East Africa

Abstract

There is limited information on the distribution of B. pfeifferi, an important snail intermediate host of schistosomiasis, in East Africa. This study assessed the incidence and geographical distribution of B. pfeifferi snails in Kenya, Uganda and Tanzania. Maximum Entropy modeling was used to predict the potential distribution of B. pfeifferi snails, in line with habitat suitability. Malacological surveys were then conducted guided by MaxEnt predictions and information obtained from previous research papers. The surveys were conducted at a total of 156 sites including streams, rivers, lake shores, dams and irrigation canals over a 3 year period (2018 to 2020). Geographical coordinates, ecological and physicochemical information was recorded for the sites visited. Snails were identified morphologically, based on shell characters using established identification keys. B. pfeifferi snails were found at 23.07% (36/156) of the sites sampled. Streams proved to be the habitats most preferred by B. pfeifferi snails (50% of all of the sites where the snails were found were streams), followed by rivers (20.6%), irrigation canals (8.8%), lake shores (8.8%), springs (5.9%), and dams (5.9%) with snail abundance increasing with increase in temperature and decrease in water depth. B. pfeifferi was found in the Lake Victoria basin, Mwea Irrigation Scheme and Eastern Province of Kenya, the Lake Albert region, Lango region, Soroti district, Lower Moshi irrigation scheme, Babati district, Iringa region, Tabora region and Kigoma region. Information on the distribution of B. pfeifferi in East Africa will aid in developing prevention and control strategies for schistosomiasis.AUTHOR SUMMARYFew studies have been conducted on the distribution of B. pfeifferi snails in East Africa with previous studies mostly isolated projects restricted to single divisions, districts and regions. Knowledge on the distribution of snail intermediate hosts can be helpful in establishing schistosomiasis transmission surveillance systems for detecting emerging and prevailing incidences of schistosomiasis. We undertook malacological surveys of freshwater sites across Kenya, Uganda and Tanzania. A total of 156 sites were sampled and B. pfeifferi snails were found at 36 of the sites. Streams yielded the highest number of snails, in comparison to the other habitats that were sampled. Temperature and water depth were established to be statistically significant ecological and physicochemical factors that influence incidences and abundance of the snails. This study provides important information on the distribution of an important snail intermediate host in East Africa and the knowledge obtained herein can be helpful in establishing appropriate schistosomiasis control initiatives.

A machine learning approach for modeling the occurrence of the major intermediate hosts for schistosomiasis in East Africa

“…In our study, with an NDVI range of 0.18 to 0.83 and an LST range of 3.4 to 43.6 °C in the region, both parameters exhibited low significance in determining the distribution of both genera (by MDG). This observation aligns with previous studies conducted by Magero et al 26 , Boitt and Suleiman 56 , and Deka 46 , all of which found a similar limited influence of these two parameters on the presence of IH snails. Nonetheless, it is important to consider that we have observed in this study that land cover has a limited influence at all.…”

“…The land cover classification employed in this study distinguishes 17 land cover classes, including 11 natural vegetation classes (such as forests, open herbaceous areas, and wetlands), 3 human-altered classes (comprising agricultural land and built-up areas), and 3 non-vegetated classes (including snow, rocks, and water bodies). Furthermore, various physiochemical properties previously studied for their effects on IH snail distribution 14 , 26 , 46 were integrated into our analysis. This included soil pH, soil organic carbon content in fine earth, and soil cation exchange capacity obtained at a 30 m resolution at a depth of 0–20 cm and 20–50 cm from the Innovative Solutions for Decision Agriculture Ltd (iSDA) data set via Google Earth Engine 47 .…”

“…Currently, only one documented study exists for East Africa region as a whole, albeit restricted to Biomphalaria IHs and a limited number of surveyed locations, considering just eight predictor features 26 . This previous study gives a first impression, however, obtaining robust results may necessitate the inclusion of a broader array of potential features in the analysis.…”

A first alert of Biomphalaria pfeifferi in the Lower Shire, Southern Malawi, a keystone intermediate snail host for intestinal schistosomiasis

“…Biomphalaria snails serve as the obligate intermediate host of Schistosoma mansoni, a parasitic blood uke that causes intestinal schistosomiasis [1, 2, 3]. Biomphalaria pfeifferi is commonly found in East Africa (e.g., Kenya, Uganda and Tanzania [4,5]). However, until this report, its presence in the Lower Shire River valley was unknown.…”