Showing papers on "Bulinus truncatus published in 1999"

Distribution of freshwater snails in the man-made Oyan Reservoir, Ogun State, Nigeria

Abstract: The factors influencing patterns of snail distribution in Oyan Reservoir, a typically medium sized man-made reservoir in southwest Nigeria, were investigated once a month, for 28 months (August 1990-November 1992). During each monthly visit, seven stations were sampled for relative snail density, vegetation cover and physical and chemical properties of the lake water. Statistical analyses were performed to determine the influence of these factors on snail abundance and distribution. Seven aquatic snail species were found in the reservoir, namely Bulinus globosus, B. forskalii, B. truncatus, Lymnaea natalensis, Indoplanorbis exustus, Potadoma freethi and Potadoma moerchi. The relative proportion of these species was 17.6% (B. globosus), 16.1% (B. forskalii), 0.2% (B. truncatus), 12.9% (L. natalensis), 23.4% (I. exustus) and 29.8% (both Potadoma spp. combined) of 28 183 snails collected over the study period. The seasonal trends of the species were variable but basically bimodal with peaks in August (rainy season) and November/December (early dry season). These trends were similar to the water level and rainfall patterns, suggesting that seasonal changes in snail density were probably influenced by these factors. Spatial distribution of each snail species was similar along each shoreline but significantly different across the E-W transect. Similar trends occurred for conductivity, dissolved oxygen and biochemical oxygen demand suggesting that these factors may have affected snail distribution across shorelines. Ten species of aquatic vegetation were identified, six of which correlated positively and significantly with various snail species. The most important of the associating vegetation was Impatiens irvingii which correlated with all snail species and served as an indicator plant for Indoplanorbis exustus, an introduced snail species in Nigeria.

Schistosomiasis in newly reclaimed areas in Egypt. 2--Patterns of transmission.

Abstract: The distribution, abundance and seasonality of infected Biomphalaria alexandrina and Bulinus truncatus were studied for 2 years (1992-1994) in two newly reclaimed areas, namely El Manayef and El-Morra areas located on both sides of Suez Canal near Ismailia City. The results confirm the occurrence of transmission of both Schistosoma mansoni and S. haematobium since infected snails of both species were recovered in these areas. This consequently proves that reclamation of parts of the desert utilizing Nile water had led to spread of schistosomiasis to these areas. Analysis of the data shows that the infected snails, especially B. alexandrina, were found clustered in a relatively few numbers of transmission sites and furthermore the greater majority of these sites were found located within a less number of transmission foci. This pattern of focality is clearly demonstrated by Geographical Information System (GIS) produced maps. Infected B. alexandrina snails fluctuated seasonally showing 2 peaks, a minor peak in August and a higher one in November. Only one peak of infected B. truncatus was recognized in July.