Freshwater snail diversity in relation to Schistosomiasis in the middle Zambezi basin in Lusaka Province
Date
2011-03-31
Authors
Mubita, Patricia
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Abstract
This study was carried out at the Middle Zambezi basin in Lusaka province to determine
freshwater snail diversity, its relationship to the presence of schistosomiasis and the
impact of prevailing environmental factors on snail diversity. The study was carried out
during the cool-dry season (July), hot-dry season (October) and hot-wet season
(February), from July 2006 to February 2007. Twenty 400 metre transects were
established on three rivers, ten streams and one reservoir. Snails were sampled every four
metres on each transect using a scoop net. Each transect was divided into five 80 metre
segments. Environmental data consisting of physical, chemical and biotic data was
obtained at the mid point of every segment. Physical data collected consisted of water
depth, temperature and velocity. Chemical data collected consisted of conductivity, pH
and calcium concentration. Biological data collected was vegetation by type and genera,
and phytoplankton diversity.
Fifteen species of freshwater snails were collected from the study area. Pulmonate
species consisted of Bulinus globosus, Bulinus forskalli, Bulinus canescens,
Biomphalaria pfeifferi, Segmentorbis angustus, Gyraulus costulatus, Lymnaea natalensis,
Physa acuta and Ferrissia burnupi burnupi. The prosobranch species consisted of
Bellamya cappillata, Cleopatra nsendwensis, Gabbiella kisalensis, Gabbiella sp, Lanistes
ovum and Melanoides tuberculata. Linear regression was used to determine the
relationship between snail diversity (species richness) and the number of infected
children at the schools in close proximity to the water sampling points. There was a
significant relationship between snail diversity (in the presence of the intermediate snail
host) and schistosomiasis prevalence. Snail diversity explained 62% of the variance in
schistosomiasis prevalence. Results of the study demonstrated that in the presence of high
species diversity of snails, transmission of Schistosoma haematobhim is lower.
Multiple regression analysis (Best Sub Set) revealed that water velocity was the most
important factor affecting snail diversity in the rivers, while conductivity was the most
important factor in the streams. Snail diversity was significantly different among the
different vegetation types. All the floating vegetation types were associated with higher
snail diversity whereas Phytoplankton diversity was not significantly associated with
snail diversity.
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Keywords
Schistosomiasis--Zambia