Biodegradability of the molluscicidal saponins of Phytolacca dodecandra.

The biodegradability of water-extracted saponins of berries from the Endod plant, Phytolacca dodecandra L'Herit, was evaluated under OECD standardized conditions. Persistence of the saponins was evaluated by determination of saponin concentrations in water over a 30-day period, using a quantitative HPLC method and a semiquantitative hemolytic assay, which is considered a potential field method. The two methods were compared. Bioassays were simultaneously conducted using Biomphalaria glabrata fresh water snails to assess the molluscicidal potency over time. All experiments were carried out in water, which was chemically balanced to sustain snails, and to one set river water was added to the medium to mimic natural conditions. (1) Saponin concentrations in water treated with an aqueous extract of P. dodecandra cultivar E44 were stable for 2 days then rapidly decreased during the third and fourth day. Lethal concentrations to snails were LC50 = 9.6 mg/l (95% CI: 6.3 to 19.4) in one set and LC50 = 6.8 mg/l (95% CI: 5.4 to 12.2) in the other. Adding river water to one set of the experiments had no effect on the mean saponin concentration over time (F = 0.02, P = >0.05). (2) Comparison of the hemolytic assay with the HPLC method showed no significant difference in mean saponin concentrations (t = 0.32, P > 0.05, 95% CI: -2.67 to 3.64), and a correlation of r2 = 0.88 between the two methods. (3) The saponin fraction of an aqueous extract of P. dodecandra was readily biodegraded (t1/2 = 15.8 h), and the complete consumption within a 10-day window indicates ready degradability in aquatic environments under aerobic conditions. (4) These results show that the use of Endod berries for snail control in schistosomiasis-infested water bodies is environmentally acceptable.

The molluscicidal activity of coumarins from Ethulia conyzoides and of dicumarol.

The molluscicidal principles of Ethulia conyzoides were identified as ethuliacoumarin A (1) and isoethuliacoumarin A (2). Ethuliacoumarin A possessed an LC90 between 19 and 23.5 ppm depending on the age of the snail against Biomphalaria glabrata, and between 12 and 15 ppm against Bulinus truncatus. In addition, ethuliacoumarin A was found to be cercaricidal at 25 ppm and ovicidal. Ethuliacoumarin has the structural requirements considered essential for anticoagulant activity. Consequently the anticoagulant dicumarol (4) was tested and found to be molluscicidal in the range from 2.5 to 10 ppm. In contrast, the coumarin anticoagulant warfarin (3) did not show molluscicidal activity.

Molluscicidal trials and correlation between the presence of Tetrapleura tetraptera in an area and the absence of the intermediate hosts of schistosomiasis and fascioliasis in southwest Nigeria.

A schistosomiasis research project, carried out in Southwest Nigeria, yielded data by which it was possible to relate snail recovery from potential transmission sites to the presence or absence of Tetrapleura tetraptera. A significant negative correlation with snail numbers was found for distance of T. tetraptera from transmission sites and fruiting of the trees when these variables were tested individually. There were no significant differences between individual variables such as pH, Ca2+ concentrations and temperatures for these snail habitats but these variables produced significant positive correlation with the number of snails recovered. Thus, the presence of T. tetraptera appeared to be the most important limiting factor for the presence of snails. Aqueous extracts of T. tetraptera were effective as a molluscicide against Bulinus globosus and Lymnaea natalensis. However, pollution of the environment by oils reduced or abolished the molluscicidal activity of T. tetraptera. The results indicate that the planting of T. tetraptera has potential for the local control of schistosomiasis.

Molluscicidal and antischistosomal activities of Zingiber officinale.

Experiments were conducted to study the major constituents of Zingiber officinale responsible for its molluscicidal activity and the effect of the active component on different stages of Schistosoma mansoni. Gingerol and shogaol exhibited potent molluscicidal activity on Biomphalaria glabrata. Gingerol (5.0 ppm) completely abolished the infectivity of Schistosoma mansoni miracidia and cercariae in B. glabrata and mice, respectively, indicating that the molluscicide is capable of interrupting schistosome transmission at a concentration lower than its molluscicidal concentrations.

Evaluation of aridanin, a glycoside, and Aridan, an aqueous extract of Tetrapleura tetraptera fruit, on Schistosoma mansoni and S. bovis.

Experiments were conducted on different stages of Schistosoma mansoni and S. bovis using various concentrations of aridanin and Aridan. Aridanin and Aridan were active against Schistosoma mansoni and S. bovis miracidia. A low concentration of aridanin (0.25 micrograms/ml) reduced the production of cercariae by snails already shedding cercariae. Aridanin and Aridan also produced profound reduction in the worm recovery of mice infected with pretreated cercariae of S. mansoni and S. bovis. Higher concentrations of the molluscicides were biocidal to the cercariae of these schistosomes. These results indicate that the molluscicides are capable of reducing the transmission of schistosomiasis at different stages of the schistosome development and suggest that a similar effect may occur under field conditions.