Molluscicidal activities of selected plant extracts on Bulinus truncatus snails from Schistosoma endemic areas, White Nile, Sudan

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Muataz Ahmed, Abdalla
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This study was conducted as an up-date of the epidemiology of human and animal Schistosomiasis in El.Duiem Rural Area, the White Nile State and to investigate the molluscicidal potency of some indigenous plants as possible biological control agents against Bulinus truncatus snails, the intermediate host of the Schistosoma haematobium and Schistosoma bovis. The study on the epidemiology of Schistosomiasis was done in the Northern part of El.Duiem town in three selected villages, namely, Al.Oshara, Al.Hussien and Goz Al.Baid. The incidence of Schistosoma haematobium and Schistosoma bovis was determined during the three seasons of the year Dec. 2005 –Jan. 2007 conventionally identified as cool dry, hot dry and rainy season. School children of the age group 5-19 years were included in the investigation. Besides, fifty head of cattle in the same villages were also included. Al.Oshara and Al.Hussien villages represented the highest rates of incidence due to the existence of the main irrigation canals, where water current is slow, favoring snail colonization. Goz Al.Baid village had a low rate of infection due to the location of the village on the Nile bank, with a faster water flow rate. The incidence rate fluctuated for both Schistosoma haematobium in the examined urine samples and Schistosoma bovis in faecal samples. The overall incidence of Schistosoma haematobium and Schistosoma bovis were 19.9% and 6.6% respectively. The highest rate of incidence was recorded in Al.Hussien village in the hot dry season, being 40.9% for Schistosoma haematobium and 16.1% for Schistosoma bovis. The lowest rate was recorded in Goz Al.Baid village in the cool dry season, being 3.1% for Schistosoma haematobium and 0% for Schistosoma bovis. In relation to age, the overall pattern of incidence in school children showed slight increase in 10-14 year age group, being 21.1% as compared to the other age groups. The substantial difference was observed between age groups 10-14 and 15-19, being significant at P>95%. The difference was significant between calves (13.4%) and adult (2.3%) cattle. The relation between humans and bovine Schistosomiasis and sex were studied. In humans it was revealed that the incidence rate was higher in males (24.3%) than females (14.7%). Comparing cattle examination results it was recorded that higher rates were in females (8.2%) than males (5.9%), as most of the calves belong to the female group. The seasonal fluctuation of Bulinus truncatus snail infection and their transmission pattern was recorded. The infection rates of snails fluctuated throughout the seasons, Al.Hussien had the highest rate during the hot dry season (17.3%), yet infection was detected at lower rates during the other two seasons. Al.Oshara had low rates compared to Al.Hussien, and Goz Al.Baid was having the lowest infection of snails. The infection in this last village was below detection level during the cool dry season. The infection with the two Schistosoma species was coinciding with infection rates in school children and cattle. The laboratory verification using naturally infected snails as a source of cercariae to infect mice revealed 15% bovine Schistosomiasis versus 85% of haematobium. As it was evident, Schistosomiasis remained to be a threat for man and his livestock. Control measures, however refined need to be simplified and to consider socio-economic limitations. Biological control, using herbal extracts will keep being one of the attractive alternatives where indigenous plants can be screened for molluscicidal activities. In this study this was considered if some active ingredients are to be applied for extensive water bodies. Laboratory evaluation of the molluscicidal activity of leaf extract of Calotropis procera and Nicotiana tabacum and the seed of Trigonella foenum plants were carried out against Bulinus truncatus snails. The results of mortality were statistically analyzed using probit analysis. The assessment of the lethal concentration for 50% and 95% of the snail was tested (LC50 and LC95). The low values of LC95 against adult, juveniles and egg masses of snails were recorded in Calotropis procera being 1100ppm, 483ppm and 31ppm respectively. Comparing the LC95 values of the water extracts of the three plants against adult snails, showed high activity for Calotropis procera plant (1100ppm), followed by Nicotiana tabacum plant (1386ppm), then Trigonella foenum plant (2085ppm). Toxicity screening of the aqueous extract of Calotropis procera and Nicotiana tabacum was carried out in mice as biological models. The results obtained after oral dosing with each of the two extracts showed some obvious congestion in blood vessels of liver in mice been fed on extract of Nicotiana tabacum plant. Calotropis procera did not cause obvious pathological changes in the animals used. This study could be a pilot attempt to be followed by more detailed studies in the laboratory and field to include the screened plants in the list of plant molluscicides
Molluscicidal,plant extracts,Bulinus truncatus snails,endemic areas, White Nile, Sudan